
Class 
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CHEMISTRY 



INORGANIC AND .ORGANIC 



Richter's Chemistry. 

A Standard and Popular Text-Book. 

EACH VOLUME SOLD SEPARATELY. 

Vol. I, Cloth, $2.00. Vol. II, Cloth, $3.00. 

Vol. I. — Inorganic Chemistry. From the Fourth German Edition. 89 

Wood-cuts and Colored Lithograph of Spectra. 
Vol. II. — The Chemistry of Carbon Compounds, or, Organic 
Chemistry. From the Fourth German Edition. Illustrated. 

Authorized Translations by 

EDGAR F. SMITH, M.A., Ph.D., 

Prof, of Chemistry in Wittenberg College, Springfield, Ohio ; formerly in the 
Laboratories of the University of Pennsylvania and Mu1ile?iberg Col- 
lege ; Member of the Chemical Societies of Berlin and 
Paris, of the Academy of Natural Sciences 
of Philadelphia, etc., etc. 

In most of the chemical text-bocks of the present day, one of the 
striking features and difficulties with which teachers have to contend is 
the separate presentation of the theories and facts of the science. These 
are usually taught apart, as if entirely independent of each other. In this 
work, which has been received with such hearty welcome, theory and fact 
are brought close together, and their intimate relation clearly shown. 
From careful observation of experiments and their results, the student is 
led to a correct understanding of the interesting principles of chemistry. 
The matter is so arranged as to adapt the work to the use of the beginner, 
as well as for the more advanced student of chemical science. 

From F. A. Genth, Prof, of Chemistry; F. A. Genth, Jr., Ass't Prof of Chemistry, 

Univers ty of Pennsylvania. 

" We have examined with much care the ' Inorganic Chemistry ' of Prof. Victor von 
Richter, recently translated by Dr. E. F. Smith. Roth theoretical and general chemis- 
try are treated in such a clear and comprehensive manner that it has become one of the 
leading text-books for a University course in Germany. We are indebted to Dr Smith 
for his translation of this excellent work, which may help to facilitate the study of 
chemistry in this country." 

This work is now recommended at Dartmouth College, Hanover, N. H.; 
Rensselaer Polytechnic Institute, Troy, N. Y. ; Wittenberg College, Spring- 
field, Ohio; University of Pennsylvania, Philadelphia; Muhlenberg Col- 
lege, Allentown, Pa.; West Virginia State University, Morgantown; 
Swarthmore College, near Philadelphia; Wisconsin State University, 
Madison; Trinity College, Hartford, Conn., and many other Schools and 
Colleges. 

*V Correspondence is invited from teachers and professors of chemistry 
in reference to the introduction of these books. Each volume sold sepa- 
rately. 

P. BLAKISTON, SON & CO., 
Medical Publishers and Booksellers, 

1012 WALNUT STREET, PHILADELPHIA. 



CHEMISTRY 



INORGANIC AND ORGANIC 



WITH EXPERIMENTS 



CHARLES LOUDON BLOXAM 

PROFESSOR OF CHEMISTRY IN KING'S COLLEGE, LONDON; IN THE DEPARTMENT 01 

ARTILLERY STUDIES, WOOLWICH; AND FORMERLY IN THE 

ROYAL MILITARY ACADEMY, WOOLWICH. 



FIFTH EDITION, CAREFULLY REVISED. 
WITH 292 ILLUSTRATIONS. 



PHILADELPHIA : 

P. BLAKI8T0N, SON & CO., 

No. 1012 Walnut Street. 
1885. 






In Exchange 
Brown University 

MAY 2 6 ia# 






EXTEACTS 



PREFACE TO THE FIRST EDITION 



This work is designed to give a clear and simple description of 
the elements and their principal compounds, and of the chemical 
principles involved in some of the most important branches of 
manufacture. Keeping this in view, I have employed as few 
technical terms as possible, especially at the commencement, so 
that the student may glide into Chemistry without having first 
to toil through a difficult chapter on the terminology of the 
science, which he can never appreciate until he has become 
acquainted with the examples which serve to illustrate its appli- 
cation. 

Convinced, by experience, of the great assistance afforded to 
the learner by referring him to a simple illustrative experiment, 
I have introduced, generally in smaller type,. a description, and 
in most cases a wood engraving, of the experiments which I 
have found most useful in illustrating lectures, hoping that these 
may prove of service in fixing the attention of the student, and 
may assist those who are desirous of performing such experiments 
for their own instruction, or for that of a class. 

In general, English weights and measures, and Fahrenheit ther- 
mometric degrees, have been employed, as conveying more clearly 
to the beginner the absolute values expressed, since the mental 
effort of converting what must still be called the Continental 
systems, slight though it be, might have the effect of diverting 
the attention of the reader from the chemical question under 
consideration. The various calculations have been conducted in 
the simplest arithmetical form, because the more compendious 



VI PREFACE. 

algebraical expressions are not so generally intelligible, and when 
the principle is once understood, a general algebraical formula for 
the calculation is easily constructed by the learner. 

The special attention devoted to Metallurgy and some other 
branches of Applied Chemistry, will render the work useful to 
those who are being educated for employment in manufacture. 

The military student will find more than the usual space allotted 
to the Chemistry of the various substances employed in warlike 
stores. 

The attention of the student is called to the Table of Contents, 
which has been drawn up to serve the purpose of an abstract, by 
which he may examine himself upon each paragraph of the book. 
The Index is also a dictionary of the most important formulae, in 
which either the name of a compound may be referred to, in order 
to find its formula, or the formula may be sought when it is 
desired to ascertain the compound to which it belongs. 



The Fifth Edition has been carefully revised, and some altera- 
tions have been made in the theoretical portion, to bring it into 
harmony with modern views. 

The Table of Atomic Weights (at page xxiv) has been arranged 
so as to indicate the quantivalence of the elementary bodies. 

King's College, London, 
March 1883. 

%*. In the following pages, the smaller type contains not only 
the descriptions of experiments, but all such matter as would be 
of less importance to a student desiring only a general knowledge 
of the subject without going into details. 



TABLE OE CONTENTS, 



Paragraph 

Introduction. — Definitions, Molecules, Atoms, Law of Avogadro, Mole- 
cular and atomic weights, ...... 1 

Enumeration and classification of elements, with their symbols, use of 
symbols and equations, chemical attraction, combination, and 
decomposition, ....... 2 

Classification of compounds into organic and inorganic, . . 3 

Chemistry of the Non-metallic Elements and their Compounds. 
Water — Analysis of water by the galvanic battery ; construction of 

Grove's battery, . . . . . . .4 

Electrolysis j electro-positive and electro-negative elements, . . 5 

Relative volumes of hydrogen and oxygen in water ; difference in 

application of electricity according to quantity and tension, . 6 

Decomposition of steam into detonating gas by heat and electric 

sparks, ........ 7 

Disengagement of hydrogen from water by metals, . . 8 

Definition of an alkali ; definition of chemical equivalent of a 
metal j action of potassium and sodium on water ; classification 
of metals according to their action upon water, . . 9 

Hydrogen. — Preparation of hydrogen by action of red hot iron upon 

steam ; by action of zinc or iron upon diluted sulphuric acid, . 10 

Physical properties of hydrogen ; its value as a theoretical unit of 

volume ; illustrations of its extreme lightness, . . . 11-12 

Diffusibility of gases defined and illustrated ; separation of hydrogen 

and oxygen by atmolysis ; law of the velocities of diffusion, . 13 

Chemical properties of hydrogen ; character of its flame, . . 14 

Explosive mixtures of hydrogen with air and oxygen, . . 15 

Oxygen. — Its occurrence in nature, . .... 16 

Physical properties of oxygen. Specific gravity of gases defined, . 17 
Chemical properties of oxygen. Combustion, . . . 18 

Relations of oxygen to phosphorus ; effects of heat and minute divi- 
sion upon chemical attraction ; nature of acids ; anhydrides, 19 
Relations of oxygen to sulphur, . . . . . 20 

Relations of oxygen to carbon, . . . .21 

Etymology of oxygen. Definition of an acid, . . .22 

Relations of oxygen to the metals ; sodium and oxygen, . .23 

Relations of oxygen to zinc ; definition of base, salt, . . 24 

Relations of oxygen to iron ; naming oxides to indicate their com- 
position ; definition of a metal, . . . . .25 

Indifferent oxides, . . . . . . .26 

Preparation of oxygen from atmospheric air, . , .27 

„ „ manganese dioxide, . . .28 

Preparation of oxygen from potassium chlorate ; calculation of the 

weight of a given volume of gas, . . . . .29 



Vlll CONTENTS. 



Paragraph 

30 
31 

32 
33 
34 
35 

36 



Water. — Synthesis of water from its elements, . 

Explosion of hydrogen and oxygen in the eudiometer, 
Eudiometric analysis of air, .... 

Synthesis of vapour of water, .... 

Synthesis of water by weight, .... 

Keciprocal character of combustion, 

Oxyhydrogen blowpipe, .... 

Chemical relations of hydrogen; Hijdrogenium ; occlusion of hydrogen 

by palladium, . . ■ . . . .37 

Chemical relations of water to other substances ; hydrates ; nature of 
simple solution ; crystallisation from water ; super-saturated 
solutions, . . . . . . . 38 

Efflorescence ; water of crystallisation and water of constitution of 

salts ; deliquescence, . . . . . .39 

Hydrated bases, . . . . . .40 

Hydroxjde the radical of the hydrates or hydroxides, . . 41 

Water from various natural sources ; air dissolved in water, . . 42 

Saline components of natural waters ; hardness ; boiler incrusta- 
tions ; petrifying springs ; stalactites ; processes for softening- 
waters ; temporary and permanent hardness ; organic matter 
in waters. Tests for purity of water, . . . .43 

Action of water upon leaden cisterns and pipes. Testing of water for 

lead. Mineral waters, ...... 44 

Sea- water, . „ . . . . .45 

Purification of water by distillation ; the still and worm ; Liebig's 

condenser, ....... 46 

Physical properties of water ; specific gravity of liquids and solids 

defined ; definition of boiling-point, . . . .47 

Hydric peroxide ; its preparation and properties ; decomposition 

by contact ; positive and negative oxygen, . . .48 

Ozone : its constitution and production ; ozonic ether ; Dr. Day's 

test for blood, ....... 49 

Atmospheric air. — Its composition ; rough demonstration of the pro- 
portions of oxygen and nitrogen by phosphorus ; exact analysis 
of air by copper, . . . . . . .50 

Air a mixture, not a chemical compound ; functions of the nitrogen 

in air ; uniform composition of the atmosphere maintained by 

diffusion ; dialysis of air ; Sprengel's air-pump ; dust in air, . 51 

Carbon. — Its natural varieties ; demonstration of the nature of 

diamond ; exact synthesis of. carbonic acid gas ; graphite ; its 

useful applications, . . . . . . .52 

Artificial varieties of carbon ; lamp-black, wood-charcoal ; destructive 
distillation defined ; charcoal-burning ; decolorisation and deo- 
dorisation by charcoal ; animal charcoal ; calorific value of 
carbon, ........ 53 

Coal. — Chemistry of its formation ; composition and special uses of 
• lignite, bituminous coal and anthracite ; spontaneous combustion 

of coal, ... . . . . . .54 

Oxides of carbon ; their composition by weight, . . . 55 

Carbonic acid gas. — Sources of atmospheric carbonic acid gas ; respira- 
tion ; fermentation ; decomposition of carbonic acid by plants, . 56 



CONTENTS. IX 

'Paragraph 
Occurrence of carbon dioxide in the mineral kingdom ; preparation 

of carbonic acid gas, . . . . . .57 

Properties of carbonic acid gas ; illustrations of its high specific 
gravity and power of extinguishing flame; limit to combustion 
of a taper in confined air ; limit to respiration of animals in 
confined air ; noxious effects of carbonic acid gas ; principles of 
ventilation ; solubility of carbonic acid gas in water ; spark- 
ling drinks ; importance of dissolved carbonic acid to plants, . 58 
Liquefaction of carbonic acid gas in glass tubes and in iron 
cylinders ; continuity of the gaseous and liquid states of matter ; 
experiments with the solidified gas, . . . .59 

Separation of carbon dioxide from other gases, . . .60 

Ultimate analysis of organic substances ; calculation of formulae exem- 
plified; empirical and rational formulae, . . . .61 

Salts formed by carbonic acid. Table of the commonest carbonates, 

with their common names, additive and substitutive formulae, 62 
Analytical proof of the composition of carbon dioxide, . . 63 

Carbonic oxide. — Its formation in fires and furnaces ; its poisonous 

character, ......... 64 

Formation of carbonic oxide by passing steam over red-hot carbon ; 

its useful application, ...... 65 

Carbonic oxide compared with carbonic acid gas, . . .66 

Preparation of carbonic oxide ; from oxalic acid ; from potassium 

ferrocyanide, . . . . . . .67 

Reduction of metallic oxides by carbonic oxide ; preparation of 

pyrophoric iron, . . . ._ . . .68 

Composition by volume of carbonic oxide and carbon dioxide, . 69 
Atomic weight of carbon, ...... 70 

Compounds of carbon and hydrogen ; formulae of acetylene, marsh gas, 

and olefiant gas, . . . . . . .71 

Acetylene. — Its production by direct synthesis ; its preparation in 
quantity by the imperfect combustion of coal gas ; new radicals 
derived from acetylene ; cupros-ethenyle, argent-ethenyle ; 
fulminating argent-ethenyle hydrate ; remarkable properties of 
acetylene; formation of sty role by action of heat upon acetylene ; 
synthesis of prussic acid with acetylene and nitrogen, . . 72 

Olefiant gas. — Its preparation and properties ; formation of Dutch 
liquid ; production of acetylene from olefiant gas by the spark- 
ling discharge, ....... 73 

Marsh gas. — Its occurrence in nature ; fire-damp ; preparation and 
properties of marsh gas ; chemistry of explosions in coal-mines ; 
safety-lamps ; fire-damp indicator, . . . .74 

Structure of flame; cause of luminosity in ordinary flames; experiments 
illustrating the structure of flame ; influence of the supply of air 
upon the character of flames ; smokeless gas-burners ; effect of 
atmospheric pressure upon the luminosity of flames ; com- 
position of illuminating fuels, . . . . .75 

The blowpipe flame. — Functions of its different parts ; reduction of 

metals by the blowpipe, on charcoal ; hot-blast blowpipe, . 76 

Eudiometric analysis of marsh gas, . . . . .77 

Coal gas. — Products of the distillation of coal, .."■-. . . 78 



CONTENTS. 



Paragraph 



Silicon. — Its occurrence as silica in nature ; conversion of silica into a 
soluble form ; preparation of pure silica by dialysis ; crystallised 
and amorphous silica, ...... 

Apparatus for effecting fusions in the laboratory, 

Silicates ; tetra-basic character of silicic acid, .... 

Preparation and properties of silicon ; amorphous, graphitoid, and 

adamantine silicon ; comparison of silicon with carbon ; hydride 

and nitride of silicon ; atomic weight of silicon, 

Boron. — Boracic acid ; its extraction from the sojjioni ; properties of 

boracic acid ; its antiseptic character ; borates, 

Extraction of boron from boracic anhydride ; amorphous and diamond 

boron, . . . ' . . 

Review of carbon, boron, and silicon, . 
Nitrogen. — Its occurrence in nature and preparation from air ; inert 
character of the element, and activity of its compounds, 
Ammonia. — An important medium of circulation for nitrogen 
extraction from the ammoniacal liquor of the gas-works ; sub 
limation ; preparation of ammonia gas ; solution of ammonia 
mode of ascertaining its strength ; liquefaction of ammonia 
Carre's refrigerator ; combination of ammonia with acids 
the ammonium-theory ; formation of ammonium-amalgam, 
Atomic weight and volume of nitrogen, 
Process for ascertaining the proportion of nitrogen in an organic 

substance ; calculation of the formula of urea, . 
Formation of ammonia in the rusting of iron ; nascent state of 
elements ; ammonia from atmospheric nitrogen, 
' Production of nitrous and nitric acids from ammonia ; nitrification 
formation of nitrates in nature ; nitrifying ferment, 
Compounds of nitrogen and oxygen, 
Nitric acid. — Preparation in the laboratory and on the large scale ; pro- 
perties of nitric acid ; its action upon metals and organic substances. 
Oxidising effects of nitrates, ...... 

Anhydrous nitric acid or nitric anhydride. Table of the chief 

nitrates, with their common names and formulae, 
Nitrous oxide ; preparation from ammonium nitrate, 
Nitric oxide ; rough analysis of air by nitric oxide, 
Nitrous acid ; preparation of potassium nitrite, 
Nitric peroxide ; commercial nitrous acid, 

General review of the oxides of nitrogen ; combination -in multiple 

proportions ; determination of the composition of the oxides of 

nitrogen ; tabular review of their composition, 

Chlorine. — Its occurrence in nature and extraction from common salt ; 

Weldon's and Deacon's chlorine processes. Striking physical and 

chemical properties of chlorine ; powerful attraction for non-metallic 

and metallic elements, ...... 

Relations of chlorine to hydrogen ; synthesis of hydrochloric acid 
effected by natural and artificial light ; displacement of oxygen 
from water by chlorine ; action of chlorine upon other hydrogen- 
compounds ; substitution of chlorine for hydrogen in organic 
substances ; oxidising action of moist chlorine, 
Bleaching properties of chlorine ; their application, 



79 

80 
81 



82 

83 

84 
85 



»7 

88 

89 

90 

91 
92 

93 
94 

95 
96 
97 
98 
99 

100 



101 



102 
103 



CONTENTS. 



XI 



104 
105 



106 

107 

108 
109 
110 



111 
112 



Paragrapl 

Chloride of lime. — Mode of using it for "bleaching, and for printing 
white patterns on a coloured ground ; disinfecting properties of 
chlorine ; application of chloride of lime for disinfecting, 
History of the discovery of chlorine ; phlogiston, 
Hydrochloric acid. — Preparation and properties of the gas ; production 
of solution of hydrochloric acid in the alkali works. Weak acid 
properties of liquefied hydrochloric acid, .... 

Action of hydrochloric acid upon metals ; demonstration of its 
composition by volume, ...... 

Action of hvdrochloric acid upon basic metallic oxides ; formation 
of chlorides, ...... 

Action of hydrochloric acid on indifferent oxides and anhydrides, . 
Compounds of chlorine with oxygen, .... 

Hypochlorous acid. — Its use for erasing ink ; the hypochlorites ; 
preparation of oxygen from chloride of lime. Chloride of 
soda, . . . . . . . 

Chloride of lime, its relation to hypochlorous acid, 
Chloric acid. Chlorate of potash ; preparation ; from potassium car- 
bonate ; from potassium chloride. Preparation and properties 
of chloric acid. Useful applications of potassium chlorate. Com- 
bustion of potassium chlorate in coal gas. Coloured fire com- 
positions. Anomalous evolution of heat in the decomposition of 
the chlorates, ...... 

Perchloric acid. — Explosive properties, .... 

Chloric peroxide. — Its unstable character and powerful oxidising action 

Euchlorine, ... 
Chlorous anhydride ; chlorous acid ; chlorites, . 

General review of the oxides of chlorine ; their composition by 
volume, ....... 

CJilorides of carbon. — Preparation of the bichloride or tetrachloride 
Composition by volume of the chlorides of carbon. Influence o 
the composition by volume of a compound upon its properties 
Table of the molecular formula?, weights and volumes of the 
chlorides of carbon, ..... 

Phosgene gas or carbon oxychloride, .... 

Silicon tetrachloride. Boron trichloride, 

Chloride of nitrogen. — Processes for preparing it ; violent explosive 

character, . 

Aqua regia. Nitrosyle chloride, .... 

Bromine. — Extraction from the waters of mineral springs ; great chemica 
resemblance to chlorine ; hypobromous and bromic acids, . 
Hydrobromic acid. Bromide of nitrogen. Chloride of bromine, 
Iodine. — Extraction from ashes of sea-weed. Characteristic properties 
of iodine and the iodides, . - 
Iodic acid. Periodic acid, 

Hydriodic acid. — Its powerful reducing properties : carbon tetra-iodide 
Iodide of nitrogen. — Explosive character ; iodammonium iodide, 
Chlorides and bromides of iodine, .... 

Potassium iodide. — Its preparation. Ferrous iodide, . 
Fluorine. — Fluor spar, ...... 

Hydrofluoric acid ; etching on glass. Fluorides ; kryolite, 



113 

114 

115 
116 

117 



118 
119 
120 

121 
122 

123 
124 

125 
126 
127 
128 
129 
130 
131 
132 



Xll CONTENTS. 

Paragraph 
Silicon tetrafluoride ; its decomposition by water, . . 133 

H ydrofluosilicic acid ; silicofluorides, . . . . .134 

Boron trifluoride j fluoboric and hydrofiuoboric acids, . . 135 

General review of chlorine, bromine, iodine, and fluorine, . .136 

Sulphur. — Its occurrence in nature ; composition of the principal sul- 
phides and sulphates found in the mineral kingdom. Extraction 
of sulphur in Sicily. Refining of sulphur. Distillation of sulphur 
from pyrites. Commercial varieties of sulphur, . . .137 

Properties of sulphur ; remarkable transformation by heat ; electro- 
positive and electro-negative sulphur ; soluble and insoluble 
varieties ; octahedral and prismatic sulphur ; table of the chief 
allotropic forms of sulphur, . . . . .138 

Influence of temperature upon the specific gravity of gases and 

vapours ; anomalous expansion of sulphur vapour, . .139 

Hydrosulphuric acid. — Its preparation for laboratory use ; prepara- 
tion of sulphide of iron. Properties of sulphuretted hydrogen ; 
action upon metals and their oxides ; blackening of paint, 
pictures, &c, by impure air ; use of hydric sulphide in analysis ; 
sulphur acids, bases, and salts ; action of air upon metallic 
sulphides, . . . . . . . .140 

Hydric persulphide, . . . . . . .141 

Compounds of sulphur with oxygen, . . . .142 

Sulphurous acid. — Its bleaching and antiseptic properties. Sulphites, 143 
Sulphuric acid; Nordhausen oil of vitriol; gradual development of 
the English manufacture of oil of vitriol ; experiments illustra- 
ting the theory of the process ; preparation of oil of vitriol in 
the laboratory and on the large scale ; plan for economising 
nitric oxide ; commercial varieties of sulphuric acid. Properties 
of oil of vitriol; its action upon organic substances and upon 
metals, . . . . . . . .144 

Sulphuric anhydride; its formation from sulphur dioxide and 

oxygen, • , 145 

Sulphates. Action of sulphuric acid upon metallic oxides. 
Normal, acid and double sulphates. Decomposition of sul- 
phates by heat and by reducing agents. Table of the chief 
sulphates, with their common names and formulae, . .146 

Hyposulphurous or thiosulphuric acid. — Hyposulphite of soda or 
sodium thiosulphate ; its preparation and use for fixing photo- 
graphic prints, and for making antimony vermilion. Hydrosul- 
phurous acid, . . . . . . .147 

Hijposulphuric or dithionic acid, . . . . .148 

Trithionic or sulphuretted hyposulphuric acid, . . . .149 

Tetrathionic or bisulphuretted hyposulphuric acid, . . .150 

Pentathionic acid, . . . . . . .151 

Bisulphide of carbon. — Its use in spectrum analysis ; its diathermanous 
character and inflammability ; a starting-point for the synthesis 
of organic compounds. Sulphocarbonates. Removal of carbon 
disulphide from coal gas. Preparation and properties of carbon 
oxysulphide, . . . . . . .152 

Silicon disulphide, . . . . . . .153 

Nitrogen sulphide. — Its explosive character, . . . .154 



CONTENTS. Xlll 

Paragraph 
Chlorides of sulphur. — Preparation of the subchloride or chloride of 

sulphur. Iodides of sulphur, . . . . .155 

Selenium. — Its extraction from the deposit in the vitriol chambers. 
Selenious and selenic acids. Selenietted hydrogen. Chlorides and 
sulphides of selenium ; use of selenium in the photophone, . 156 

Tellurium. — Tellurous and telluric acids ; telluretted hydrogen ; 

chlorides and sulphides of tellurium, . . . .157 

Review of the sulphur group of elements, comprising sulphur, sele- 
nium, and tellurium, . . . . . .158 

Phosphorus. — Its distribution in nature ; extraction from bones on the 
large and small scales ; action of light on phosphorus. Phosphor- 
escence. Allotropic modifications of phosphorus. Preparation of 
red phosphorus. Precipitation of metals by phosphorus, . .159 

Lucifer matches ; silent matches ; safety matches, . . .160 

Armstrong fuze composition ; amorces fulminant es, . .' . 161 

Oxides of phosphorus. — Table of their composition, . . . 162 

Phosphoric acid. — Its natural sources ; preparation from bones. Phos- 
phoric anhydride. Metaphosphoric, pyrophosphoric, and ortho- 
phosphoric acids, . . . . . . .163 

Phosphorous acid,; phosphites. Hypophosphoric acid, . . .164 

Hypophosphorous acid, . . . . . . .165 

Suboxide of phosphorus. — Combustion of phosphorus under water, . 166 
Phosphides of hydrogen. — Preparation and properties of phosphuretted 

hydrogen gas, . . . . . . .167 

Chlorides of phosphorus. — Oxychloride and sulpho chloride of phos- 
phorus ; sodium sulphoxyphosphate. Action of iodine on phos- 
phorus, ........ 168 

Sulphides of phosphorus, . . . . . .169 

Action of ammonia on oxychloride and pentachloride of phosphorus. 

Amides of phosphoric acid, . . . . .170 

Arsenic. — Formulae of natural arsenides and arseniosulphides. Extrac- 
tion of arsenic from mispickel. Properties and chemical relations 
of arsenic, . . . . . .' . .171 

Oxides of arsenic. Arsenious acid. — Composition of arsenious and 

arsenic acids. Arsenites. Scheele's green, . . . 1 72 

Arsenic acid. — Sodium arseniate, . . . . .173 

Arsenietted hydrogen. — Marsh's test for arsenic. Composition and 
molecular formula of arsenietted hydrogen. General review of 
ammonia, phosphuretted and arsenietted hydrogen, . .174 

Arsenic trichloride and tribromide, . . . . .175 

Arsenic di- and tri-odides and trifluoride, . . . .176 

Sulphides of arsenic. Eealgar. King's yellow, . . 177 

General review of the non-metallic ELEMENTS.^-Classincation 
according to their atomicities. Elucidation of the constitution of 
compound bodies by the doctrine of atomicity. Structural formulae. 
Bonds, . . . . . . . 178 

Constitution of salts. — Haloid and oxy-acid salts. Difference 
between neutral and normal salts. Criterion of normality. Water- 
type theory. Constitution of polybasic acids and their salts. 
Hydroxyle theory of acids, .'...-. . 179 



XIV CONTENTS. 

Paragraph 
CHEMISTRY OF THE METALS. 

Classification of metals. — Periodic law of the chemical elements 
Potassium. — Its occurrence in nature. Potassium carbonate 
Potassium hydrate. Extraction of potassium. Blowpipe test for 
potassium. Potassium chloride. Bicarbonate of potash, 
Sodium. — Extraction of salt. Salt gardens of Marseilles, 

Manufacture of carbonate of soda from common salt. Soda ash. Soda 
crystals. Soda-lye. Alkali waste. Sodium hydrate, 
Extraction of sodium from the carbonate. Uses of sodium, 
Borax. Refining of tincal. Crystallisation of borax, 
Silicate of soda. Soluble glass. Artificial stone. Sulphate of soda 
Phosphate of soda, 
Salts of ammonium, .... 

Sulphate of ammonia or ammonium sulphate, 
Sesquicarbonate of ammonia or ammonium carbonate, 
Ammonium chloride ; its dissociation by heat, 
Ammonium sulphide, .... 

Lithium. — Lepidolite, petalite, spodumene. Lithia. Lithium 
bonate. Rubidium. Gcesium, 
Spectrum analysis, .... 

General review of the group of alkali-metals, 
Barium. — Preparation of barium-compounds from heavy spar. Barium 

nitrate and hydrate. Barium dioxide, chloride and chlorate, 
Strontium. — Preparation of strontium nitrate, . 
Calcium. — Carbonate of lime; its various mineral forms. Lime 
burning. Sulphate of lime. Preparation of plaster of Paris 
Calcium chloride, calcium sulphide ; luminous paint, 
General review of the metals of the alkaline earths, . 
Relation between specific heats and atomic weights. Atomic heats, 
Magnesium. — Extraction and properties of the metal. Preparation of 

magnesium sulphate and carbonate. Magnesium chloride, 
Zinc. — Properties upon which its usefulness depends. Galvanized iron 
Ores of zinc. Distillation of zinc. English method of extracting 
the metal from its ores. Belgian and Silesian processes. Oxide, 
sulphate, and chloride of zinc, . 200 

Cadmium. — Sulphide and iodide of cadmium, . . . • 201 

Glucinum, ........ 202 

Aluminium. — Minerals containing alumina. Composition of clay. 

Manufacture of alum. Alumina. Aluminium chloride, . . 203 

Extraction of aluminium from bauxite. Sodium aluminate. Pro- 
perties and uses of aluminium, . .... 204 

Mineral silicates of alumina. Exchange of isomorphous metals in 

minerals. Natural and artificial ultramarine, . . • 205 

Thorinum, Yttrium, Erbium, Lanthanium, Didymium, Zirconium, 206-210 
Gallium, Indium, ...... 211-212 

Cerium, Uranium, ..... . • 213-214 

Iron. — Its occurrence in nature. Ores of iron. Table of composition 

of British iron ores, . . . . . • .215 

Metallurgy of iron. — Its physical properties, .... 216 



180 
181 

182 
183 
184 

185 
186 
187 
188 
189 
190 

191 
192 
193 

194 

195 



196 
197 
198 

199 



CONTENTS. XV 

Paragraph 

English process of smelting clay iron-stone. — Blast-furnace. Chemical 
changes in the blast-furnace. Composition of gas from blast- 
furnace. The hot blast. Composition of slag from the blast- 
furnace, ........ 217 

Cast-iron. — Composition of different varieties of cast-iron. Grey, 

mottled, and white iron. Chill casting, . . . .218 

Conversion of cast-iron into bar-iron. — Refining. Puddling. Varieties 
of bar-iron. Chemical effect of puddling and forging on cast- 
iron. Composition of tap-cinder. Defects of the puddling 
process. Bessemer's process. Conditions influencing the strength 
of bar-iron, ........ 219 

Manufacture of steel— The cementation process. Shear steel. Pro- 
duction of cast-steel. Hardening and tempering steel. Case- 
hardening. Malleable cast-iron. Bessemer steel. Spiegel- eisen. 
Ferromanganese. Homogeneous iron. Puddled steel. Natural or 
German steel. Siemens-Martin steel. Krupp's cast-steel, . 220 

Direct extraction of wrought-iron from the ore. — The Catalan process, . 221 
Extraction of iron on the small scale. Sefstrom furnace, . . 222 

Chemical properties of iron. Passive state of iron, . . . 223 

Oxides of iron. Ferrous oxide. Ferric oxide. Magnetic oxide of 

iron. Ferric acid, . . . . . .224 

Ferrous sulphate. Ferric sulphate, .... 225 

Perchloride of iron or ferric chloride, .... 226 

Atomic weight of iron. Varying atomicity of iron. Ferrosum and 

ferricum, ....... 227 

Cobalt. — Cobaltous and cobaltic oxides, . - . . 228 

Nickel. — Oxides, sulphate, and sulphides of nickel, . . . 229 

Manganese, ........ 230 

Oxides of manganese. Manganous and manganic oxides ; manganese 
dioxide. Manganic acid. Permanganic acid. Potassium 
permanganate, . . . . . . .231 

Chlorides of manganese. Recovery of waste manganese, . . 232 

Chromium. — Preparation of bichromate of potash from chrome-iron, . 233 

Chromic acid. Potassium chromate. Chrome yellow. Oxides of 

chromium. Perchromic acid, ..... 234 

Chromous and chromic chlorides. Chlorochromic acid. Fluoride 

and sulphide of chromium. Sulphochromites, . . . 235 

General review of zinc, iron, cobalt, nickel, manganese, and chromium, 236 

Molybdenum, Vanadium . . . . . 237-239 

Bismuth. — Extraction and properties. Fusible alloy, . . . 240 

Bismuthous and bismuthic oxides. Bismuthic acid, . , . 241 

Trisnitrate of bismuth or flake-white. Pearl-white. Bismuth tri- 
chloride. Bismuthous and bismuthic sulphides, . . . 242 
Antimony. — Extraction of regulus of antimony. Amorphous antimony, 243 
Oxides of antimony. Antimonic acid. Antimoniate, metantimo- 

niate and bimetantimoniate of potassium, . . . 244 

Antimonietted hydrogen, ...... 245 

Antimony trichloride and pentachloride, .... 246 

Sulphides of antimony. Mineral kermes. Schlippe's salt, . . 247 

Tin. — Cornish treatment of tin ores. Extraction and purification of tin, 248 



XVI CONTENTS. 

Paragraph 

Physical properties of tin. Manufacture of tin-plate. Tinning of 

copper vessels, ....... 249 

Alloys of tin. Solder. Gun metal. Bronze. Bell metal, . . 250 

Oxides of tin. Stannous oxide. Stannic oxide. Preparation of 

stannate of soda. Metastannic acid, . . . .251 

Stannous chloride or tin-crystals. Stannic chloride or nitromuriate 

of tin. Pink salt, ...... 252 

Sulphides of tin. Preparation of mosaic gold, . . . 253 

Titanium. — Titanic acid ; its extraction from iron-sand. Other com- 
pounds of titanium, ....... 254 

Tungsten. — Preparation of tungstate of soda from wolfram. Dialysed 
tungstic acid. Oxides, chlorides, and sulphides of tungsten. 
Tungstoborates, ....... 255 

Niobium, Tantalum, ....... 256 

Copper. — Its occurrence in nature. Ores of copper. Copper pyrites, 

Malachite. Grey copper ore, .... 257 

Smelting of copper ores. — Calcining the ore. Copper smoke. Fusion 
for coarse metal. Calcining the coarse metal. Fusion for white 
metal. Roasting the white metal. Refining the blister copper. 
Toughening or poling. Underpoled and overpoled copper. Table 
of products obtained in smelting copper ores, . . . 258 

Extraction of copper from copper pyrites in the laboratory, . 259 

Effect of impurities upon the quality of copper. Phosphor- 
bronze, ....... 260 

Properties of copper, . . . . . . .261 

Effect of sea water upon copper. Muntz metal, • . . . 262 

Danger attending the use of copper vessels in cooking food, ' . 263 

Alloys of copper with other metals. — Table of their composition. Brass. 

Bronzing. Aich metal. Sterro metal, .... 264 

Oxides of copper. Cupric and cuprous oxides. Quadrantoxide. 

Cupric acid, ....... 265 

Sulphate of copper. Carbonates and silicates of copper, . . 266 

Chlorides of copper. Oxychloride ; Brunswick green. Cuprous 

chloride, ........ 267 

Sulphides of copper. Extraction of copper by kernel-roasting. 

Cuprous sulphide. Copper pyrites. Phosphide of copper, . 268 
Lead. — Its useful qualities. Ores of lead. Galena, . . . 269- 

Smelting of galena. Old English process. Economico-furnace, . 270 

Improving process for hard lead, . . .- . .271 

Extraction of silver from lead. — Pattinson's process for concentrating 

silver in lead, ....... 272 

Cupellation of argentiferous lead. Sprouting of silver, . . 273 

Extraction and cupellation of lead in the laboratory, . .274 

Uses of lead. Type metal. Shot. Solder, . . . 275 

Lead pyrophorus. Oxides of lead. Litharge. Minium. Lead 

peroxide, ....... 276 

Manufacture of white lead. — Dutch process. Pattinson's process. 

Carbonate, sulphate, and phosphate of lead, . . . 277 

Chloride and oxychloride of lead. Turner's yellow. Lead iodide, 278 
Sulphides, chlorosulphide, and selenide of lead, . . . 279 



CONTENTS. XV 11 

Paragraph 

Thallium. — Its discovery by the spectroscope. It position among the 

metals, ........ 280 

Silver. — Extraction of silver from copper by liquation. Amalgamation 
of silver ores. Standard silver. Plating and electro-plating. 
Silvering glass. Preparation of pure silver, . . . 281 

Properties of silver, ....... 282 

Oxides of silver. Preparation and nses of nitrate of silver. Permanent 

ink, ........ 283 

Chloride of silver. Becovery of silver from photographic baths. 

Subchloride, bromide, iodide, and sulphide of silver, . . 284 

Mercury. — Extraction from cinnabar at Idria and Almaden. Purifica- 
tion of mercury, ....... 285 

Medicinal preparations of metallic mercury, .... 286 

Uses of mercury. Silvering looking-glasses. Amalgams, . . 2b7 

Mercurous and mercuric oxides. Mercuramine, . . . 288 

Mercurous and mercuric nitrates and sulphates, . . . 289 

Chlorides of mercury. Corrosive sublimate. White precipitate, . 290 
Calomel. Its preparation and properties. Mercurous and mercuric 

iodides, . . . . . . . .291 

Sulphides of mercury. Preparation of vermilion, . . . 292 

Platinum. — Treatment of platinum ores by the wet and dry processes. 

Spongy platinum. Platinum black, .... 293 

Platinous and platinic oxides. Preparation of platinic chloride. Its 
double salts with alkaline chlorides. Platinous chloride. Its 
behaviour with ammonia. Platosamine and platinamine, . 294 

Palladium. — Its separation from platinum ores, ..... 295 

Ehodium. — Extraction of the metal from rhodio-chloride of sodium, . 296 
Osmium. — Osmic acid. Chlorides of osmium, .... 297 

Euthenium. — Oxides of ruthenium. Euthenic acid, . . . 298 

Iridium. — Extraction from the native osmiridium allo} r , . . 299 

Tabular view of the analysis of platinum ores. Summary of the 

group of platinoid metals, ...... 300 

Davtum, . . . . . . . . . 301 

Gold.— Washing for gold dust. Smelting of auriferous ores ; with lead ; 
with pyrites. Amalgamation of gold ores. Standard gold. Testing 
and assaying gold, ....... 302 

Physical properties of gold. Gold leaf. Euby gold. Manufacture of 

gold thread. Gilding, ...... 303 

Oxides and chlorides of gold. Fulminating gold. Sel cVor. Purple of 

Cassius, ........ 304 

Chemical principles of the manufacture of glass. — Window glass. 
Plate glass. Crown and Flint Glass. Production of coloured 
glasses, ........ 305 

Chemistry of the manufacture of pottery and porcelain. — Sevres 
porcelain. English porcelain. Stoneware. Earthenware. Bricks. 
Dinas firebricks. Blue bricks, ..... 306 

Chemistry of building materials. — Varieties of building stones. 
Freestone. Portland and Bath stones. Magnesian limestones. Test 
of resistance of building stones to frost. Mortar. Hydraulic 
cements. Concrete, ....... 307 

b 



XV1U CONTENTS. 

Paragraph 
Gdnpowder. — Nitre or saltpetre. Grough nitre. Conversion of sodium 
nitrate into potassium nitrate. Artificial production of nitre 
in the nitre heaps. Saltpetre-refining. Properties of saltpetre. 
Relation to combustible bodies. Charcoal for gunpowder. Composi- 
tion of charcoal prepared at different temperatures. Sulphur for 
gunpowder. Tests of its purity. Functions of sulphur in gun- 
powder. Manufacture of gunpowder. Incorporation. Pressing. 
Granulating or corning. Glazing, ..... 308 

Properties of gunpowder. — Effects of air, water, and heat upon 

powder, ........ 309 

Products of explosion of gunpowder. — Difference in results obtained by 

different experimenters. Most recent experiments, . .310 

Calculation of the force of fired gunpowder. — Gas furnished by calcula- 
tion from a given quantity of powder. Temperature of the gas at 
instant of explosion. Specific heats of the products of explosion. 
Expansion of the gas by heat. Mechanical equivalent of gun- 
powder. Effect of size of grain on the firing of powder. Blasting- 
powder, . . . . . .. . .311 

Effect of variations of atmosplieric pressure on the combustion of gun- 
powder. — Manufacture of gunpowder in the laboratory, . . 312 
Chemistry of fuel. — Calorific value of fuel calculated. Theoretical 
and actual calorific values. Difference between calorific value and 
calorific intensity. Calculation of the calorific intensity of carbon 
burning in oxygen and in air. Calculation of the calorific intensity 
of hydrogen burning in air. Calculation of the calorific intensity 
of fuel containing carbon, hydrogen, and oxygen. Theoretical and 
actual calorific intensities. Waste of heat in furnaces. Economy 
of heat in Siemens' regenerative furnace. Table of composition, 
calorific values, and intensities of ordinary fuels, . . .313 



ORGANIC CHEMISTRY. 

Introductory. Classification of organic compounds, . . . 314 

Cyanogen and its compounds. — History of cyanogen, . . .315 

Yellow prussiate of potash or potassium ferrocyanide. Prussian 

blue. Hydroferrocyanic acid. Hydrocyanic or prussic acid. 

Mercuric cyanide. Formylamine. Carbodiamine, . . 316 

Preparation and properties of cyanogen. Potassium . cyanide and 

cyanate. Cyamelide. Cyanic acid. Potassium sulpho-cyanide. 

Hydrosulphocyanic acid. Liebig's test for prussic acid. Chrysean. 

Cyanogen iodide, . . . . . . .317 

Red prussiate of potash or potassium ferricyanide. Turnbull's blue. 

Eerricyanogen and other compound cyanogen radicals, . .318 

Chlorides of cyanogen. Cyanuric acid. Cyanide of phosphorus, . 319 
Nitroprussides. Hadow's and Stadeler's investigation of their consti- 
tution. Economical preparation of sodium nitroprusside, . 320 
The fulminates. — Preparation of fulminate of mercury. Its properties. 

Percussion cap composition. Fulminate of silver. Experiments 

with the fulminates. Chemical constitution of the fulminates. 

Fulminurates or isocyanurates, . . . . .321 



CONTENTS. XIX 

Paragraph 

Products of the destructive distillation op coal. Manufacture 

of coal gas. Composition of coal-tar, . . . 322 

Coal-naphtha. Separation of its constituents by fractional distilla- 
tion, ........ 323 

Benzene. Benzene chloride. Trichlorhydrine ofphenose. Phenose, 324 
Aniline. Its preparation from nitrobenzene. Production of colouring 

matters from aniline, ...... 325 

Goal-tar dyes. — Mauve or aniline-purple. Mauveine. Magenta or 

aniline-red. Bosaniline and its salts. Leucaniline. Chrysani- 

line or aniline-yellow. Triphenylic rosaniline or aniline-blue. 

Ethyliodate of tri-ethyl-rosaniline. Hydrocyan-rosaniline, . 326 

Chemical constitution of aniline. Formation from phenic acid and 

ammonia. Picoline. Quinoline. Diazobenzene, . .327 

Benzene series of homologous hydrocarbons. Their relation to the 
aromatic acids. Homologous nitro-compounds and bases de- 
rived from them, . . . . . .328 

Carbolic acid. Preparation from the dead-oil of coal-tar. Examina- 
tion of commercial carbolic acid. Tribromophenole, . . 329 
Carbazotic or picric acid. Chloropicrine. The phenyle series. 

Kresylic acid, ....... 330 

Naphthalene. Magdala red. Substitution products from naph- 
thalene. Phthalic acid. Connexion of naphthalene with 
the phenyle series. Anthracene. Phenanthrene. Chrysene. 
Pyrene, ........ 331 

Products op thf destructive distillation of wood. — Proximate 
constituents of wood. Cellulose. Vasculose/ Lignine. Composi- 
tion of different woods. Products of the action of heat upon 
wood, ........ 332 

Wood-naphtha or methylic alcohol. Purification. Methyle-com- 
pounds. Oil of winter-green. Metamerism illustrated by methyle 
formiate and acetic acid, ...... 333 

Paramne. Extraction from wood-tar. Parafnneoil. Eupittonic acid. 
Stockholm tar. Petroleum. Eangoontar. Bitumen or asphaltum. 
Ozokerite. Vaseline, ...... 334 

Oil of turpentine and substances allied to it. — Colophony. Isomeric 

modifications of turpentine. Artificial camphor, . . . 335 

The turpentine series of hydrocarbons. Essential oils, . . 336 

Camphors. Common camphor. Borneo camphor, . . . 337 

Balsams. Balsam of Peru. Storax. Styrole and metastyrole, . 338 
Kesins. Copal. Lac. Amber. Varnishes. Benzoin. Benzoic 

acid, ........ 339 

Oil op bitter almonds and its derivatives — Benzoyle series. — 
Formation of bitter almond oil. Amygdaline. Emulsine. Ben- 
zoine. Benzoyle. Benzoic anhydride, .... 340 

Oil of Cinnamon. — Cinnamic acid. Cinnamyle. Cummin oil. 

Cuminic acid, ....... 341 

Salicine and its derivatives — Glucosides. — Saligenine ; its chlori- 
nated derivatives. Salicylic acid. Monobasic diatomic acids. Oil 
of spiraea. Benzoyle-salicyle. Coniferine. Vanilline, . . 342 

Populine or benzoyle salicine. Phloridzine. Quercitrine. Esculine. 

Paviine. Saponine. Picrotoxine, .... 343 



XX CONTENTS. 

Paragraph 

Essential oils containing sulphur — Allyle series. — Formation of 
essence of mustard. Myronic acid. Allyle iodide. Artificial forma- 
tion of essences of mustard and garlic. Allylic alcohol. Allylene, 344 
Gum-resins, Caoutchouc. — Vulcanised caoutchouc. Gutta percha, . 345 
Gums. — Arabine. Mucic acid. Gum tragacanth, . . . 346 

Starch. — Manufacture of starch. Composition of the potato ; of wheat ; 

of rice. Properties of starch. Sago. Tapioca, . . . 347 

Conversion of starch into dextrine and grape-sugar, . . . 348 

Germination of seeds. — Malting. — Action of diastase on starch. Com- 
position of malted and unmalted barley, and of malt-dust, . 349 
Brewing. — Composition of the hop. Nature of yeast. Alcoholic fer- 
mentation. Composition of beer. Viscous fermentation, . 350 
Acetification — Manufacture of Vinegar. The quick vinegar process, . 351 
Bread. — Composition of gluten. Process of bread-making. Aerated 

bread. Leaven. New and stale bread, .... 352 

The Sugars. — Production of sugar from cotton, paper, and other varieties 
of cellulose. Action of sulphuric acid on cellulose. Vegetable 
parchment. Hydro-cellulose ; cause of dry rot. Sugar of fruits or 
fructose. Conversion of cane-sugar into fructose, . . . 353 

Extraction of cane-sugar. — Vacuum pans. Sugar-refining, . . 354 

Beetroot sugar. Maple sugar. Sugar-candy. Barley-sugar. Caramel, 355 
Chemical properties of the sugars. Compounds of sugar with bases. 
Action of solutions of the sugars upon polarised light Ethyle- 
glucose, ........ 356 

Mannite. Glycyrrhizine, ...... 357 

Gun-cotton and substances allied to it. — Pyroxyline. Preparation 

of gun-cotton in the laboratory, ... . . . 358 

■ Manufacture of gun-cotton. — Abel's process, .... 359 

Chemical composition of gun-cotton. Trinitro-cellulose or cellulo- 

trinitrine. Reconversion of gun-cotton into ordinary cotton, . 360 
Products of the explosion of gun-cotton. Explosion of loose and con- 
fined gun-cotton. Karolyi's experiments. Effects of gun-cotton 
and gunpowder compared, . . . . .361 

Properties of gun-cotton compared with those of gunpowder, . 362 

Behaviour of gun-cotton with solvents, .... 363 

Collodion- cotton. Action of weak nitro-sulphuric mixtures upon 
cotton. Preparation of soluble cotton for collodion. Process 
for making balloons of collodion. Artificial ivory, . . 364 

Xyloidine. Nitromannite, . . . - . 365 

Wine and Spirits. — Preparation and composition of wines. Proportion 

of alcohol in wines, ....... 366 

Distilled spirits. Brandy, whisky, gin, &c. Potato-spirit, . . 367 

The Alcohols and their derivatives. — General formula of alcohols 
of the vinic class. Table of the vinic or ethylic class of alcohols, 
with their sources, common names, and formulae. Gradation in pro- 
perties of the homologous alcohols. Table of their boiling-points 
and vapour densities. Chemical definition of an alcohol. General 
formulae for the derivation of an aldehyde, an acid, and an ether 
from an alcohol. Table of the acetic series of acids with their sources 
and formulas. General description of the acetic series. The olefines 
or olefiant gas series of hydrocarbons, .... 368 



CONTENTS. XXI 

Paragraph 

Alcohol as the type of its class. Preparation of absolute alcohol, . 369 
Ether. Continuous etherifying process. Preparation of ethylic iodide, 370 
The alcohol-radicals. — Isolation of ethyle. General formula of alcohol- 
radicals. Duplex constitution of the alcohol-radicals. Hydrides 
of alcohol-radicals or marsh gas hydrocarbons, . . .371 

Compound ethers. — Oxalic ether. Oxalovinic acid. Acetic ether. 
Nitrous ether. Nitric ether. Hydroxylamine prepared from 
nitric ether. Perchloric ether. Boracic and silicic ether. 
Carbonic ether. Formation of ethyle orthocarbonate from 
chloropicrine. Phosphovinic acid. True sulphuric ether. Oil 
of wine, ........ 372 

Sulphovinic or sulphethylic acid. Its preparation, . . 373 

Viuic acids not formed by monobasic acids, .... 374 

Theory of etherification. — Formation of double ethers, . . . 375 

Water-type view of alcohols and ethers. Potassium and sodium 

alcohols. Aluminium alcohols. Thallium alcohol, . . 376 

Sulphuretted derivatives of the alcohols. Mercaptan, . . 377 

Hydrocyanic ether, ...... 378 

Kakodyle-series — Organo-metallic bodies. — Alcarsin. Chloride of 

kakodyle. Kakodylic acid. Cyanide of kakodyle, . . 379 

Preparation and properties of zinc-ethyle. Zinc-methyle. Zinc-amyle. 
Potassium-ethyle. Sodium- ethyle. Arsenio-dimethyle or kako- 
dyle. Arsenio-diethyle or ethyle-kakodyle, . . . 380 
Arsenio-trimethyle. Arsenio-triethyle. Stibethyle. Mercuric methide. 
Aluminium ethide. Triborethyle. Boric methide. Silicium- 
ethyle, , . ..... .381 

Table of the compounds of alcohol-radicals with inorganic elements ; 
with their formulae and inorganic types. Constitution of the 
organo-metallic radicals, . . . . . .382 

Organic alkaloids — Ammonias. — Table of the alkaloids, with their 

sources and formulae. Theories of the constitution of the alkaloids, 383 
Ethylated ammonias and tlwir derivatives. — Ethylamine. Diethyla- 
mine. Triethylamine. Hydrate of tetrethylium. ' Complex am- 
monias. Diphenylamine. Alkali green, . . . 384 
Investigation of the constitution of the alkaloids. Monamines, . . 385 
Poly-ammonias ; their constitution, ..... 386 

Diamines. Ethylene-diamine. Aromatic diamines. Paraniline, . 387 
Triamines. Carbotriamine. Synthesis of guanidine. Melaniline. 

Aniline colours probably triamines, .... 388 

Tetramines. Tetrammonium-bases, ..... 389 

Ammonia-bases formed in putrefaction and destructive distilla- 
tion. Trimethylamine ; its useful applications, . . 390 
Ammonias and ammonium bases containing phosphorus, arsenic, and 

antimony. Triethyl-phosphine, . . . . .391 

Platammonium-compounds, . . . . . .392 

Amides. Oxamide. Oxamic acid, . . . . . . 393 

Nitriles. Imides, ....... 394 

Constitution of the amides. Benzamide. Salicylamide, . . 395 

Metal-amides. — Tripotassamicle. Zinc-amide. Zinc-acetimide, . 396 

Derivatives of the alcohols. — Gliloroform. Chloral, . . 397 

Perfume-ethers. — Pine-apple and pear essences. Apple-oil, . . 398 



XX11 CONTENTS. 

Paragraph 

Aldehydes. — Preparation and properties of vinic aldehyde. Aldol. 
Constitution and synthesis of the aldehydes. Oil of rue. Action 
of aldehydes on the ammonia-bases, .... 399 

Acetones or ketones. — Synthesis of acetic acetone. Methyle-valeryle 

acetone. Metacetone, ...... 400 

The essential oils regarded as aldehydes, . . . .401 

Polyatomic alcohols. Glycol. — Preparation and properties of glycol. 
Gly colic acid ; its relations to oxalic acid. Lactic series of acids. 
Conversion of the oxalic into the lactic series. Synthesis of leucie 
acid. Conversion of a diatomic into a monatomic alcohol. Water- 
type view of polyatomic alcohols, ..... 402 

Acetic acid — The fatty acid series. — Acetates. Acetone. Chlora- 

cetic acids. Synthesis of acetic acid, .... 403 

Anhydrides of organic acids. — Acetic anhydride. Duplex constitution 
of the anhydrides. Peroxides of organic radicals. Acetic and 
benzoic peroxides. Ethyle peroxide, .... 404 

Formic acid. Synthesis of formic acid. Furfurole. Butyric acid. 

Synthetical formation of acids of the acetic series. Ethacetic, 

dimethacetic, or butyric acid. Diethacetic acid. Ethylated 

and methylated acetones. Valerianic acid, . . . 405 

Separation of volatile acids by the method of partial saturation, . 406 

Soap. — Composition of the neutral fats. Stearine, oleine, palmitine. 

Action of alkalies upon them. Preparation of the fatty acids, . 407 
Candles. — Decomposition of fats by sulphuric acid. Saponification by 

superheated steam, ...... 408 

Synthesis of natural fats. — Glycerides. Boro-glyceride, . . 409 

Properties of glycerine. Acroleine. The acrylic series of acids. 

The allyle series. Glycerine formed from propane, . . 410 

Relation between glycerine and mannite. Mannite-glycericles. 

Stearic glucose. Gluco-tartaric acid, . . . .411 

Nitroglycerine. — Its preparation and properties. Dynamite, . . 412 

Oils and Fats. — Palmitine. Oleine. Margarine. Oleic acid. Sebacic 
acid. Dibasic fatty acid series. Linseed oil. Drying oils. Castor 
oil. Butter. Spermaceti. Wax. Table of the neutral fats and 
fatty acids, with their formulae, sources, and fusing-points, . .413 

Vegetable acids. — Oxalic acid. Its manufacture from sawdust. Con- 
stitution of the oxalates, ...... 414 - 

Tartaric acid. Preparation from cream of tartar. Tartar-emetic. Con- 
version of tartaric into succinic and malic acids, . - . 415 
Racemic acid. Hemihedrism of the tartrates. Dextrotartaric and 

laevotartaric acids. Analysis and synthesis of racemic acid, . 416 
Citric acid. Preparation from lemon-juice. Conversion of citric acid 

into acetic and butyric acids, . . . - . .417 

Malic acid. Extraction from rhubarb and from mountain ash berries. 

Sorbic and parasorbic acids. Asparagine, . . .418 

Tannic acid. Preparation of ink. Tanning of hides. Morocco. Kid. 

AVash-leather. Buckskin, . . . . .419 

Gallic acid. Its formation from tannic acid. Pyrogallol. Analysis 

of air by potash and pyrogallol. Phloroglucol, . . . 420 

Vegetable alkaloids. — Extraction of the alkaloids from opium. Mor- 
phine, codeine, narcotine. Meconic acid, . . . .421 



CONTENTS. XX111 

Paragraph 

Extraction of quinine from Peruvian bark. Quinoidine. Quinic acid. 

Quinone and hydroquinone, . . . . 422 

Theine or caffeine. Composition of coffee and tea. Coffee-roasting. 
Caffeol. Extraction of caffeine from them. Theobromine. Cocoa 
and chocolate. Methyle-theobromine or caffeine, . . . 423 

Strychnine. Extraction from nux vomica. Brucine. Detection of 

small quantities of strychnine. Curarine, . . . 424 

Nicotine. Extraction from tobacco. Composition of tobacco. Pre- 
paration of snuff, ....... 425 

Vegetable colouring matters. — Chlorophyll. Phylloxanthine. Phyl- 

locyanine. Colouring matters of flowers. Cyanine. Saffron. Saf- 

flower ; carthamine. Anuatto ; bixine. Weld ; luteoline. Bye-woods. 

Madder. Rubian. Alizarine. Artificial "alizarine. Turmeric, . 436 

Colouring matters prepared from lichens. — Litmus, archil, cudbear. 

Orcine. Orceine. Azolitmine. Erythrite, . . . 427 

Indigo. — Preparation of indigo blue. Indican. White or reduced 

indigo. Dyeing with indigo. Artificial indigo, . . .428 

Animal colouring matters. — Lac. Carmine, .... 429 

Dyeing and calico-printing. — Use of mordants. Dyeing red, blue, 

yellow, brown, black, ...... 430 

Printing in patterns. Resists and discharges, . . .431 

Animal chemistry. — Special difficulties attending its study. Chemistry 
of milk — Cream. Preparation of butter. Coagulation of milk. 
Preparation of lactic acid. Conversion of lactic into propionic 
acid. Preparation of cheese. Caseine. Legumine. Sugar of milk. 
Composition of milk from different animals. Adulteration of 
milk, ......... 432 

Chemistry of blood. — Composition of blood globules. Nucleine. 
Colouring matter of blood. Composition of liquor sanguinis. 
Albumen. Fibrine. Proteine. Eggs, .... 433 

Composition of flesh. — Kreatine. Inosite or sugar of flesh. Liebig's 

extract. Cooking of meat. Myosine, .... 434 

Gelatine. Chondrine. Manufacture of glue. Composition of wool 

and silk, ........ 435 

Chemistry of urine. — Urea. Artificial formation of urea. Cyanamide, 436 
Constitution of urea. Ethyl-urea. Ureides, . . . 437 

Uric acid. Alloxan. Alloxantine. Murexide, . . . 438 

Hippuric acid ; its relation to benzoic acid. Glycocoll. Average 

composition of human urine, ..... 439 

Chemistry of vegetation. — Components of the food of plants ; their 
sources. Process of formation of a fertile soil from a barren rock. 
Action of manures. Fallowing. Rotation of crops. Growth of 
plants from seeds. Ripening of fruits. Pectose. Pectine. Pectic 
and pectosic acids. Restoration of the elements of plants to the air. 
Preservation of wood from decay, . . . . . 440 

Nutrition of animals. — Chemistry of digestion. Pepsine. Composi- 
tion of bile. Taurine. Cholesterine. Chemistry of the circula- 
tion. Composition of food, . . . . . . 441 

Changes in the animal body after death. — Restoration of its ele- 
ments to the earth and air. Nature of putrefaction. Ptomaines, . 442 



XXIV 



ATOMIC WEIGHTS. 



ATOMIC WEIGHTS.* 



Aluminium, 




AT 


27t 


Mercury, 


Hg 


or Hg" 


200 


Antimony, 


. Sb' 


" or Sb v 


120J 


Molybdenum, 




Mo vi 


96 


Arsenic, 


. As'" or As v 


75 


Nickel, 


m 


or M'" 


59 


Barium, 




Ba" 


137 


Mobium, . 




Nb T 


94 


Bismuth, 


. Bi" 


' or Bi v 


210 


Nitrogen, . 


W" 


or N v 


14 


Boron, 




B'" 


10-9 


Osmium, 




Os vi 


199 


Bromine, -> 




Br' 


80 


Oxygen, 




O" 


16 


Cadmium, 


. 


Cd" 


112-3 


Palladium, . 


Pd" 


or Pd v 


106-5 


Ceesium, 




Cs'. 


133 


Phosphorus, 


F" 


or P v 


31 


Calcium, 




Ca" 


40 


Platinum, . 


Pt" 


or Pt iv 


197-1 


Carbon, 




Qiv 


12 


Potassium, . 




K' 


39-1 


Cerium, 




Ce" 


141-6 


Ehodium, . 




Ro'" 


104-3 


Chlorine, 




cr 


35-5 


Rubidium, . 




Rb' 


85-3 


Chromium, 


. Cr'" 


or Cr vi 


52-5 


Ruthenium, 




Ru ,v 


104-2 


Cobalt, 


. Co" 


or Co'" 


59 


Selenium, * . 




Se" 


79-5 


Copper, 


. Cu' 


or Cu" 


63-5 


Silicon, 




Si iv 


28 


Didymium, 




Di" 


146 


Silver, 




Ag' 


108 


Erbium, 




E" 


112-6 


Sodium, 




Na' 


23 


Eluorine, 




E' 


19 


Strontium, . 




Sr" 


87-5 


Gallium, 




Ga'" 


69-9 


Sulphur, 




S" 


32 


Glucinum, 




G" 


9-2 


Tantalum, . 




Ta v 


182 


Gold, 




An'" 


196-6 


Tellurium, . 




Te" 


129 


Hydrogen, 




H' 


1 


Thallium, . 




Tl' 


204 


Indium, 




In'" 


113-4 


Thorinum, . 




Th" 


231-5 


Iodine, 




I' 


127 


Tin, . 


Sn" 


or Sn iv 


118 


Iridium, 


. 


Ir iv 


197-1 


Titanium, 




Ti iv 


50 


Iron, . 


Fe" 


or Fe'" 


56 


Tungsten, . 




W vi 


184 


Lanthanium, 




La" 


139 


Uranium, . 


U" 


or U'" 


120 


Lead, . 




Pb" 


207 


Vanadium, . 


y/// 


orV y 


513 


Lithium, 


. 


L' 


7 


Yttrium, 


-. 


Y" 


61-7 


Magnesium, 




Mg" 


24-3 


Zinc, . 


. 


Zn" 


65 


Manganese, . 


Mn" or Mn iv 


55 


Zirconium, . 




Zr iv 


89-5 



* The accent or index affixed to each symbol expresses the number of atoms of hydrogen 
for which the atomic weight of the element is usually exchangeable in chemical combina- 
tions. (See page 247). 

f Corrected by Mallet ; formerly 27 "5. 

% Corrected by Cooke ; formerly 122. 






INTRODUCTION. 



1. Chemistry investigates and compares the properties of all the various 
kinds of matter, and endeavours to account for the difference in these 
properties. In order to do this it seeks to comprehend the relations 
between the ultimate particles or atoms of matter which are incapable of 
further subdivision. 

Matter, in a chemical sense, is anything which possesses weight. 

The finest state of division of matter with which we are acquainted is 
that of gas, the particles of which are so minute as to be invisible, so that 
on looking at a glass vessel filled with air or any other colourless gas, it 
is impossible to say whether it contains any matter or is perfectly empty, 
that is, a vacuum. The doubt may be resolved by heating the vessel, 
which would have no effect upon a vacuum, but would cause the gas to 
expand and to exert a greater pressure than before. This expansion of 
the gas proves that it consists of a number of particles which separate 
to a greater distance from each other when they are heated. These 
particles are called molecules* 

Molecules [First definition) ; the smallest physical particles of 
matter. 

(Second, definition) ; those particles of matter which may be removed 
to a greater distance from each other by the action of heat, without 
changing the identity of the matter. 

If a definite volume of gas be measured at tbe temperature of melting 
ice (0° C. ), and be then heated to a temperature of 273° C. and again 
measured, it is found to occupy twice as much space as before, showing 
that its molecules have been removed to twice the original distance from 
each other. 

This happens in the case of every gas, so long as its identity remains 
unchanged. Since this similarity in expansion by rise of temperature 
is observed for all temperatures, it is inferred that equal volumes of all 
gases at the same temperature contain the same number of molecules. 
This is commonly referred to as the Law of Avogadro. 

In the study of physical changes, a molecule, being the smallest 
physical particle of matter, may be taken as occupying unit of volume, but 
this would not be convenient in chemistry, as will appear from the follow- 
ing considerations. 

If a definite volume of hydrogen gas measured at 0° C. be raised 
to a higher temperature, its increased volume can always be calculated 
by adding to the volume at 0° as many times o-fs^d of that volume as 

* Diminutive, from moles, a mass. 



2 INTRODUCTION. 

there are degrees above 0°, since it suffers a regular expansion of -— ¥ rd of its 
bulk at 0° for each rise of 1° in temperature. 

But if a definite volume of steam be raised to a very high temperature, 
its volume is found to become half as large again as that of the hydrogen 
at the same temperature. For the steam has undergone a change in 
identity, having suffered a chemical decomposition into hydrogen and 
oxygen, and the volume of the hydrogen is twice that of the oxygen. 

Hence, if one volume of steam be raised to a very high temperature, 
it becomes one volume of hydrogen and half a volume of oxygen. 

If a molecule be taken as one volume, it would appear that one 
molecule of steam is decomposed into one molecule of hydrogen and half 
a molecule of oxygen. 

It appears then that when the identity of a gas is changed some of 
its molecules are halved; these half molecules are called atoms. There 
is no indication of the possibility of any further division. 

Atom (First definition) ; the smallest imaginable particle of matter. 

It is evidently convenient to adopt this as the chemical unit of matter, 
since it is not susceptible of any further change. 

(Second definition of an atom) ; that quantity of matter, in the state of 
gas, which occupies one volume. 

Since the half molecules are called atoms, we can give a third definition 
of a molecule as that quantity of matter in the state of gas which 
occupies two volumes. 

The action of a very high temperature upon steam, therefore, is to 
resolve or decompose two volumes or one molecule of steam into two 
volumes or atoms of hydrogen and one volume or atom of oxygen. 

But the hydrogen and oxygen are in the condition of atoms only at 
the moment of separation from each, other ; if they are subsequently 
examined, they present the ordinary physical properties of gases, show- 
ing that they are composed of molecules. Hence atoms have no 
permanent existence in a separate state, but are always united to form 
molecules. Indeed, since a molecule is the physical unit of matter, a 
half molecule would be a physical impossibility ; an atom, therefore, is a 
metaphysical conception. 

(Fourth definition of a molecide); the smallest quantity of matter which 
is capable of a separate existence. 

(Third definition of an atom); the smallest quantity of matter which is 
capable of existing in a molecule. 

It is customary to select hydrogen as the standard chemical unit with 
which all atoms and molecules are compared. This .selection is justified 
by the consideration that hydrogen is the lightest substance known, so 
that a very small weight of hydrogen admits of very accurate measure- 
ment, and the weights of the molecules of all other bodies are multiples 
of that of hydrogen. 

The unit of weight now very generally adopted by scientific chemists is 
one gramme of hydrogen, which measures 11*19 litres at 0° C. and 76 
mm. Bar. 

Hence, the unit of volume is 11 '19 litres. Since the weight of an 
atom represents the weight of one volume of a gas (by the second 
definition of an atom), it is evident that the relative weights of the atoms 
of different gases may ,be found by comparing the weights of equal 
volumes ; e. g., 



INTRODUCTION. 



11-19 litres of 
Hydrogen, weigh 1 grm. 
Oxygen, „ 16 grms. 

Xitrogen, „ 14 „ 
Chlorine, ,, 35*5 ,, 



Atomic weight. 
1 
16 
14 
35-5 



2 litres of 

weigh 2 grms. 

18 
28 
17 
71 

36-: 



-The number of grammes 



Molecular weight. 
2 
32 
18 
28 
17 
71 
36-5 
of 



simple or 
of gas at 



The relative weights of the molecules are obtained in a similar way, 
but they are referred to 2 as representing the standard molecular weight 
of hydrogen (by the third definition of molecule) ; e.g., 
11-19 
Hydrogen, 
Oxygen, 
Water-vapour, 
Nitrogen, 
Ammonia, 
Chlorine, 

Hydrochloric acid, 
Definition of atomic w eight. - 
elementary substance which occupy 11*19 litres in the state 
0° C. and 760 mm. Bar. 

Definition of molecular weight. — The number of grammes of any 
substance which occupy 22 -38 litres in the state of gas at 0° C. and 760 
mm. Bar. 

Those molecules which are composed of atoms of the same kind are 
termed Elements; those which contain atoms of different kinds are 
Compounds. The greater number of the 64 elements at present known to 
exist have not yet been measured in the state of gas, so that their relative 
atomic weights have not been determined in the manner stated above. 

But in such cases, some compound which contains the element may be 
obtained in the form of gas, and from this the relative atomic weight 
may be found. 

Second definition of atomic weight.- — The smallest weight of an 
element which can be found in two volumes (22-38 litres) of any of its 
gaseous compounds. 

Thus carbon has never been measured in the state of vapour, but its 
atomic weight is inferred to be 12 times that of hydrogen, because no 
less than 12 grammes of carbon are contained in 22-38 litres of any of the 
numerous gases formed by the combination of carbon with other elements. 
In the rare cases in which no gaseous compound of the element is 
known, the atomic weight is inferred on the grounds of chemical 
analogy, or it is ascertained from the specific heat of the element. 

2. The elements known at present are 64 in number, and are divided 
into metallic and non-metallic elements. 

The Non-Metallic Elements are (15). 



Oxvgen. 


Sulphur. 


Fluorine. 


Hvdrogen. 


Selenium. 


Chlorine. 


Nitrogen. 


Tellurium. 


Bromine. 


Carbon. 


Phosphorus. 


Iodine. 


Boron. 


Arsenic. * 




Silicon. 







* In many English chemical works arsenic is classed among the metals, which it 
resembles in some of its properties. 



INTRODUCTION. 



The Metals are (49). 



Caesium. 

Rubidium. 

Potassium. 

Sodium. 

Lithium. 

Barium. 
Strontium. 
Calcium. 
Magnesium. 


Aluminium. 

Gallium. 

Glucinum. 

Zirconium. 

Thorinum. 

Yttrium. 

Erbium. 

Cerium. 

Lanthanum. 

Didymium. 

Niobium. 


Zinc. 

Nickel. 

Cobalt. 

Iron. 

Manganese. 

Chromium. 

Cadmium. 

Uranium. 

Indium. 


Copper. 
Bismuth. 
Lead. 
Thallium. 

Tin. 

Titanium. 

Tantalum. 

Molybdenum. 

Tungsten. 

Vanadium. 

Antimony. 


Mercury. 

Silver. 

Gold. 

Platinum. 

Palladium. 

Rhodium. 

Ruthenium. 

Osmium. 

Iridium. 



The strict definition of a metal will be given hereafter. 

Many of these elements are so rarely met with, that they have not 
received any useful application, and are interesting only to the 
professional chemist. This is the case with selenium"^ and tellurium, 
among the non-metallic elements, and with a large number of the metals. 

The following list includes those elements with which it is important 
that the general student should become familiar, together with the symbolic 
letters by which it is customary to represent them, for the sake of 
brevity, in chemical writings : — 

Non-Metallic Elements of practical importance (13). 



Oxygen, 

Hydrogen, H 

Nitrogen, N 

Carbon, C 



Boron, 
Silicon, 



Sulphur, S 

Phosphorus, P 
Arsenic, As 



Fluorine, F 

Chlorine, CI 

Bromine, Br 

Iodine, I 



Metallic Elements of pr 


actical importance (26). 


Potassium, 


K (Kalium) 


Cadmium, 


Cd 


Sodium, 


Na (Natrium) 


Uranium, 


U 


Barium, 


Ba 


Copper 


Cu (Cuprum) 


Strontium, 


Sr 


Bismuth, 


Bi 


Calcium, 


Ca 


Lead, 


Pb (Plumbum) 


Magnesium, 


Mg 










Tin, 


Sn (Stannum) 


Aluminium, 


Al 


Titanium, 


Ti 






Tungsten, 


W ( Wolframium) 


Zinc 


Zn 


Antimony, 


Sb (Stibium) 


Nickel, 


Ni 






Cobalt, 


Co 


Mercury, 


Hg (Hydrargyrum) 


Iron, 


Fe (Ferrum) 


Silver, 


Ag (Argentum) 


Manganese, 


Mn 


Gold, 


Au (Aurum) 


Chromium, 


Cr 


Platinum, 


Pt 



Although the 39 elements here enumerated are of practical importance, 
many of them derive their importance solely from their having met with 



The remarkable electrical relations of selenium have led to some recent useful applica- 



tions. 



INTRODUCTION. 



useful applications in the arts. The number of elements known to play 
an important part in the chemical changes concerned in the maintenance of 
animal and vegetable life is very limited. 



Elements concerned in the Chemical Changes taking place in Life. 



Non 


■Metallic. 


Metallic. 


Oxygen. 


Sulphur. 


Potassium. Aluminium. 


Hydrogen. 




Sodium. 


Nitrogen. 


Phosphorus. 


Iron. 


Carbon. 




Calcium. Manganese. 




Chlorine. 


Magnesium. 


Silicon. 


Iodine. 





These elements will, of course, possess the greatest importance for 
those who study Chemistry as a branch of general education, since a 
knowledge of their properties is essential for the explanation of the 
simplest chemical changes which are daily witnessed. 

The student who takes an interest in the useful arts will also acquaint 
himself with the remainder of the 39 elements of practical importance, 
whilst the mineralogist and professional chemist must extend his studies 
to every known element. 

By far the greater proportion of the various materials supplied to us by 
animals and vegetables consists of the four elements — oxygen, hydrogen, 
nitrogen, and carbon; and if we add to these the two most abundant 
elements in the mineral world, silicon and aluminium, we have the six 
elements composing the bulk of all matter. 

The symbols of the chemical elements represent their atomic weights, 
thus H represents one part by weight of hydrogen, represents 16 parts 
by weight of oxygen, and C represents 12 parts by weight of carbon. 
Each symbol therefore represents one volume of the element in the 
gaseous state. 

The molecules (or two gaseous volumes) are represented, as a rule, by 
writing the figure 2 below and to the right of the symbol, thus H 2 
represents a molecule or two parts by weight, or two volumes, of 
hydrogen ; 2 = a molecule or 32 parts by weight, or two volumes, of 
oxygen. 

The mere contact or mixture of substances is expressed by the sign 
+ ; thus H 2 + Cl 2 would imply that a molecule of hydrogen had been 
brought into contact with a molecule of chlorine. 

Chemical Attraction is the force which holds the atoms of a 
molecule together. Chemical Combination is the exchange of atoms in 
one molecule for those in another, by which some new kind of matter 
is produced. For example, chemical combination takes place between 
hydrogen and chlorine, to form hydrochloric acid, the change being 
represented by the chemical equation H 2 + Cl 2 = 2HC1, which implies 
that the molecules of hydrogen and chlorine exchange atoms. 

It will be seen from the statements made above, that this equation also 
implies that 2 parts by weight of hydrogen and 35 '5 x 2 parts by weight 
of chlorine, yield 36*5 x 2 parts by weight of hydrochloric acid. 

The equation also informs us that 2 volumes of hydrogen and 2 



6 INTRODUCTION. 

volumes of chlorine would combine to form 4 volumes of hydrochloric 
acid. 

It must be remembered that a chemical equation is only a short mode 
of expressing the result of an experiment, and cannot be used like a 
mathematical equation, to effect the solution of a problem. 

A chemical equation may be written to express what is likely to result 
from the action of different molecules upon each other, but it has no value 
until verified by experiment. 

Chemical Decomposition is the separation of the atoms composing a 
molecule, which must precede the formation of a new molecule. Thus, 
the decomposition of steam by a very high temperature is expressed by 
the equation 2H 2 = 2H 2 + 2 , which conveys the information that two 
molecules or 4 volumes, or 36 parts by weight of steam, have suffered 
chemical decomposition, and have formed two molecules or 4 volumes or 
4 parts by weight of hydrogen, and one molecule or 2 volumes or 32 parts 
by weight of oxygen. 

3. Compound substances are commonly classified by the chemist into 
Organic and Inorganic compounds ; and although it is impossible strictly 
to define the limits of each class, the division is a convenient one for the 
purposes of study. 

Organic substances may be defined as those for which we are indebted 
to the operation of animal or vegetable life, such as starch, sugar, &c. 

Inorganic substances are obtained from the mineral world without the 
intervention of life ; as common salt, alum, &c. 

Organic substances always contain carbon, generally also hydrogen 
and oxygen, and very frequently nitrogen. 



INORGANIC CHEMISTRY. 



CHEMISTEY OF THE NON-METALLIC ELEMENTS 
AND THEIR COMPOUNDS.! 



THE ELEMENTS OE WATER. 



be regarded as 



4. A century has not yet elapsed since water ceased to 
an elementary form of matter. It was first resolved into its constituent 
elements, hydrogen and oxygen, by subjecting it to the influence of the 
voltaic current, which decomposes or analyses the water by overcoming 
the chemical attraction by which its elements are held together. 

An arrangement for this purpose is represented in fig. 1. 




=^P5=5 



Fig. 1. — Electrolysis of water. 

The glass vessel A contains water, to which a little sulphuric acid has been added to 
increase its power of conducting electricity, for pure water conducts so imperfectly that 
it is decomposed with great difficulty. B and C are platinum plates bent into a cylin- 
drical form, and attached to the stout platinum wires, which are passed through corks in 
the lateral necks of the vessel A, and are connected by binding screws with the copper 
wires D and E, which proceed from the galvanic battery G. H andO are glass cylin- 
ders with brass caps and stop-cocks, and are enlarged into a bell-shape at their lower 
ends for the collection of a considerable volume of gas. These cylinders are filled 
with the acidulated water, by sucking out the air through the opened stop-cocks ; on 
closing these, the pressure of the air will, of course, sustain the column of water in 



8 



ELECTROLYSIS OF WATER. 



the cylinders. G is a Grove's battery, consisting of five cells or earthenware vessels 
(A, fig. 2) filled with diluted sulphuric acid (one measure of oil of vitriol to four of 
water). In each of these cells is placed a bent plate of zinc (B), which has been 
amalgamated or rubbed with mercury (and diluted sulphuric acid) to protect it from 
corrosion by the acid when the battery is not in use. Within the curved portion of 





Fig. 3. 



Fig. 2. 
this plate rests a small flat vessel of unglazed earthenware (C), filled with strong 
nitric acid, in which is immersed a sheet of platinum foil (D). The platinum (D) of 

each cell is in contact, at its upper edge, 
with the zinc (B) in the adjoining cell (fig. 
3), so that at one end (P, fig. 1) of the 
battery there is a free platinum plate, and at 
the other (Z) a free zinc plate. These plates 
are connected with the wires D and E by 
means of the copper plates L and K, attached 
to the ends of the wooden trough in which 
the cells are arranged. The wire D (tig. 1), 
which is connected with the last zinc plate 
of the battery, is often called the "nega- 
tive pole ; " whilst E, in connexion with the 
last platinum plate, is called the "positive 
pole." 

When the connexion is established by means of the wires D and E with the " de- 
composing cell" (A), the "galvanic current" is commonly said to pass along the 

wire E to the platinum plate C, through the 
acidulated water in the decomposing cell, to the 
platinum plate B, and thence along the wire D 
tack to the battery. 

A very elegant apparatus (fig. 4) has been 
devised by Dr. Hofmann for exhibiting the de- 
composition of water by the galvanic current. 
The water displaced by the gases accumulating 
in the tubes h, o, collects in the bulb b upon the 
longer branch, and exerts the pressure necessary 
to force the gases out when the stop-cocks are 
opened. The stop-cocks being made of glass, are 
not corroded by the acid. 

5. During this " passage of the current " 
(which is only a figurative mode of express- 
ing the transfer of the electric influence), 
the water intervening between the plates B 
and C is decomposed, its hydrogen being 
attracted to the plate B (negative pole), 
and the oxygen to the - plate C (positive 
pole). The gases can be seen adhering in 
minute bubbles to the surface of each plate, 
. and as they increase in size they detach 
themselves, rising through the acidulated 
water in the tubes H and 0, in which the 
Fig. 4.— Electrolysis of water. two gases are collected. 
Since no transmission of gas is observed between the two plates, it is 




ELECTROLYSIS OF WATER. 



9 



evident that the H and separated at any given moment from each plate 
do not result from the decomposition of one particle of water, but from 
two particles, as represented in fig. 5, where A represents the particles of 
water lying between the plates P and Z before the "current " is passed, 
and B the state of the particles when the current has been established. 
P is (the positive pole) in connexion with the last platinum plate of the 
battery, and Z is (the negative pole) in connexion with the last zinc 
plate. 















































H 


H 


H 


H 


// 


H 


H 


H 




+ 


+■ 


+ 


+ 


+ 


+■ 


+ 


+ 





Fig. 5. 

The signs + and - made use of in B refer to a common mode of account- 
ing for the decomposition of water by the battery, on the supposition that 
the oxygen is in a negatively electric condition, and therefore attracted by 
the positive pole P ; whilst the hydrogen is in a positively electric condi- 
tion, and is attracted by the negative pole Z. 

The decomposition of compounds by galvanic electricity is termed elec- 
trolysis* When a compound of a metal with a non-metal is decomposed 
in this manner, the metal is usually attracted to the (negative) pole in 
connexion with the zinc plate of the battery, whilst the non-metal is 
attracted to the (positive) pole connected with the platinum plate of the 
battery. 

Hence the metals are frequently spoken of as electro-positive elements, 
and the non-metals as electro-negative. 

6. If the passage of the "current" be interrupted when the tube H has 
become full of gas, the tube will be only half full, since water contains 
hydrogen and oxygen in the proportion of two volumes of hydrogen to one 
volume of oxygen. When the wider portions of the tubes (fig. 1) are 
also filled, the two gases may be distinguished by opening the stop-cocks 
in succession, and presenting a burning match. The hydrogen will be 
known by its kindling with a slight detonation, and burning with a very 
pale flame at the jet; whilst the oxygen will very much increase the 
brilliancy of the burning match, and if a spark left at the extremity of the 
match be presented to the oxygen, the spark will be kindled into a flame. 

Another method of effecting the decomposition of water by electricity 
consists in passing a succession of electric sparks through steam. It is 
probable that in this case the decomposition is produced rather by the 
intense heat of the spark than by its electric influence. 

For this purpose, however, the galvanic battery does not suffice, since 
no spark can be passed through any appreciable interval between the wires 
of the battery, — a fact which electricians refer to in the statement that 
although the quantity of electricity developed by the galvanic battery is 
large, its tension is too low to allow it to discharge itself in sparks like 
the electricity from the machine or from the induction-coil, which pos- 
sesses a very high tension, though its quantity is small. 

7. The most convenient instrument for producing a succession of 

* "HXeKTpov (amber) — root of electricity ; Xim, to loosen. 



10 



DECOMPOSITION OF STEAM. 



electric sparks is the induction-coil, by the aid of which the electric in- 
fluence of even a weak galvanic battery may be so accumulated as to 
become capable of discharging itself in sparks, such as are obtained from 
the electrical machine. 

Fig. 6 represents the arrangement for exhibiting the decomposition of steam by 
the electric spark. 

A is a half-pint flask furnished with a cork in which three holes are bored ; in one 
of these is inserted the bent glass tube B, which dips beneath the surface of the water 
in the trough C. 




Fig. 6. — Decomposition of steam by electric sparks. 

D and E are glass tubes, in each of which a platinum wire has been sealed so as 
to project about an inch at both ends of the tube. These tubes are thrust through 
the holes in the cork, and the wires projecting inside the flask are made to approach 
to within about xgth °f an inch, so that the spark may easily pass between them. 

The flask is somewhat more than half filled with water, the cork inserted, and the 
tube B allowed to dip beneath the water in the trough, the wires in D and E being 
connected with the thin copper wires passing from the induction-coil F, which is 
connected by stout copper wires with the small battery G. 

The water in the flask is boiled for about fifteen minutes, until all the air con- 
tained in the flask has been displaced by steam. When this is the case, it will be 
found that if a glass test-tube (H) filled with water be inverted* over the orifice of 
the tube B, the bubbles of steam will entirely condense, with the usual sharp rattling 
sound, and only insignificant bubbles of air will rise to the top of the test-tube. If 
now, whilst the boiling is still continued, the handle of the coil (F) be turned so 
as to cause a succession of sparks to pass through the steam in the flask, large 
bubbles of incondensable gas will accumulate in the tube H. This gas consists of 
the hydrogen and oxygen gases in a mixed state, having been released from their 
combined condition in water by the action of the electric sparks. The gas may be 
tested by closing the mouth of the tube H with the thumb, raising it to an upright 
position, and applying a lighted match, when a sharp detonation will indicate the 
recombination of the gases, f 

It has long been known that a very intense heat is capable of decomposing water. 
The temperature required for the purpose is below the melting-point of platinum, as 
may be shown by the apparatus represented in fig. 7. 

A platinum tube (t) is heated by the burner b, the construction of which is shown 
at the bottom of the cut. It consists of a wide brass tube, from which the coal gas 
issues through two rows of holes, between which oxygen is supplied through the holes 
in the narrow tube, brazed into a longitudinal slit between the two rows of holes in 
the gas tube. The oxygen is supplied from a gas bag or gas-holder, with which the 
pipe (o) is connected. 

b The flask (/) containing boiling water is furnished with a perforated cork, carrying 
a brass tube (a), which, slips into one end of the platinum tube, into the other end of 

* The end of the tube B should be bent upwards and thrust into a perforated cork with 
notches cut down the sides. By slipping this cork into the neck of the test-tube, the latter 
will he held firmly. 

t With a powerful coil, a cubic inch of explosive gas may be collected in about fifteen 
minutes. 



ACTION OF METALS ON WATER. 



11 



which another brass tube (c) is slipped ; this is prolonged by a glass tube attached by 
india-rubber, so as to deliver the gas under a small jar standing upon a bee-hive shelf 
in a trough. 
The platinum tube is not heated until the whole apparatus is full of steam, and no 




Fig. 7. — Decomposition of steam by heat. 

more bubbles of air are seen to rise through the water in the trough ; the gas burner 
is then lighted, and the oxygen turned on until the platinum tube is heated to a very 
bright red heat ; bubbles of the mixture of hydrogen and oxygen resulting from the 
decomposition of the water may then be collected in the small jar, and afterwards 
exploded by applying a flame. 

8. In the preceding experiments, the force of chemical attraction hold- 
ing the particles of oxygen and hydrogen together in the form of water, 
has been overcome by the physical forces of heat and electricity. But 
water may be more easily decomposed by acting upon it with some 
element which has sufficient chemical energy to enable it to displace 
the hydrogen. 

^N"o non-metallic element is capable of effecting this at the ordinary 
temperature. 

Among the practically important metals, there are five which have so 
powerful an attraction for oxygen that it is necessary to preserve them in 
bottles filled with some liquid free from that element, such as petroleum 
(composed of carbon and hydrogen), to prevent them from combining 
with the oxygen of the atmosphere. These metals are capable of decom- 
posing water with great facility. 

Metals which decompose water at the ordinary temperature. — Potassium, 
Sodium, Barium, Strontium, Calcium. 

9. When a piece of potassium is thrown upon water, it takes fire and 
burns with a fine violet flame, floating about as a melted globule upon the sur- 
face of the water, and producing in the act of combination enough heat to 
kindle the hydrogen as it escapes. The violet colour of the flame is due 
to the presence of a little potassium in the form of vapour. The same 
results ensue if the potassium be placed on ice. The water in which the 
potassium has been dissolved will be found soapy to the touch and taste, 
and will have a remarkable action upon certain colouring matters. Paper 
coloured with the yellow dye turmeric becomes brown when dipped in it, 
and paper coloured with red litmus {archil) becomes blue. Substances 
possessing these properties have been known from a very remote period 



12 ALKALIES AND ACIDS. 

as alkaline substances, apparently because they were first observed by the 
alchemists in the ashes of plants called kali. 

The alkalies are amongst the most useful of chemical agents. 

Definition of an alkali. — A compound substance very soluble in water, 
turning litmus blue and turmeric brown. 

These alkaline properties are directly opposed to the characters of sour 
or acid* substances, such as vinegar or vitriol, which change the blue 
litmus to red. 

When an acid liquid such as vinegar (acetic acid) or vitriol (sulphuric 
acid) is added to an alkaline liquid, the characteristic properties of the 
latter are destroyed, the alkali being neutralised. 

An acid substance may be known by its property of neutralising an 
alkali (either entirely or partly). 

The minute investigation into the action of potassium upon the water 
would require considerable manipulative skill. It would be necessary to 
weigh accurately the potassium employed, to evaporate the resulting 
solution in a silver basin (most other materials being corroded by the 
alkali), and after all the water had been expelled by heat, to ascertain the 
composition of the residue by a chemical analysis. 

It would be found to contain by weight, 1 part of hydrogen, 16 parts 
of oxygen, and 39*1 parts of potassium. 

Since water contains 2 parts by weight of hydrogen, combined with 
16 parts of oxygen, it is evident that the product of the action of potas- 
sium on water is formed by the substitution of 391 parts of potassium 
for 1 part of hydrogen. 

It is found that whenever potassium takes the place of hydrogen in a 
compound, 39*1 parts of the former are exchanged for one of the latter, and 
this is generally expressed by stating that 39 1 is the chemical equivalent 
of potassium. 

The chemical equivalent of a metal expresses the weight wdiich is 
required to be substituted for one part by weight of hydrogen in its 
compounds. 

The action of potassium upon water is an example of the production of 
compounds by substitution of one element for another, a mode of forma- 
tion which is far more common than the production of compounds by 
direct combination of their elements. 

If the symbol K be taken to represent 39'1 parts by weight of potas- 
sium, its action upon water would be represented by the chemical equation 

H 2 + K = KOH + H. 

Water. Caustic potash. f 

But since the atoms cannot exist, except in combination as molecules, 
it would be strictly correct to write the equation thus : 

2H 2 + K 2 = 2KOH + H 2 . . 

Since the molecular equation can always be obtained by doubling the 
atomic equation, the latter will be most commonly given in this work, 
as involving fewer numbers." 

* From aKn, a point, referring to the pungency or sharpness of the acid taste. 

f Caustic, from Kaiw, to burn, in allusion to its corrosive properties ; and potash, from 
its having been originally prepared from the washings of wood ashes boiled down in iron 
pots and decomposed by lime. 



ACTION OF METALS ON WATER. 



13 




Sodium has a less powerful attraction for oxygen than potassium, and 
does not usually take fire when thrown into cold water, although it is at 
once fused by the heat evolved. By holding a lighted match over the 
globule as it swims upon the water, the hydrogen may be kiudled, when 
its flame is bright yellow, from 
the presence of the sodium. The 
solution will be found strongly 
alkaline from the soda produced. 
By placing the sodium on a piece 
of blotting paper laid on the water, 
it may be made to ignite the 
hydrogen spontaneously, because 
the paper keeps it stationary, and 
prevents it from being so rapidly 
cooled by the water. Several cubic 
inches of hydrogen may easily be 
collected by placing a piece of 
sodium as large as a pea in a small 
wire-gauze box (A, fig. 8), and holding it under an inverted cylinder (B) 
filled with water and standing on a bee-hive shelf. 

The product of the action of sodium upon water contains 1 part by 
weight of hydrogen, 16 of oxygen, and 23 of sodium, so that the 23 parts 
of sodium have been exchanged for, or been found chemically equivalent 
to, 1 part of hydrogen. 

Taking the symbol Na to present 23 parts by weight of sodium, its 
action would be expressed thus — 

H 2 + Na = NaOH + H. 

Caustic soda. 

Barium, strontium, and calcium decompose water less rapidly than 
potassium and sodium. 

The tendency of heat to separate the elements of water being known, 
it might be expected that metals which refuse to decompose water at the 
ordinary temperature, would be induced to do so if the temperature were 
raised, and accordingly magnesium and manganese, which are without 
action upon cold water, decompose it at the boiling point, disengaging 
hydrogen, and producing magnesia (MgO, a feebly alkaline earth), and 
oxide of manganese (MnO). 

But the greater number of the common metals must be raised to a much 
higher temperature than this in order to enable them to decompose water. 
The following metals will abstract the oxygen from water at high tem- 
peratures, those at the commencement of the list requiring to be heated 
to redness (about 1000° F.), and the temperature required progressively 
increasing until it attains whiteness for those at the end of the list. 

Metals which decompose ivater at a temperature above a red heat. — 
Zinc, Iron, Chromium, Cobalt, Nickel, Tin, Antimony, Aluminium, Lead, 
Bismuth, Copper. 

The noble metals, as they are called, which exhibit no tendency to 
oxidise in air, are incapable of removing the oxygen from water, even at 
high temperatures. 

Metals which are incapable of decomposing water. — Mercury, Silver, 
Gold, Platinum. 



14 



PREPARATION OF HYDROGEN. 



Metals decompose water more readily when they are placed in a state of electrical 
polarisation by contact with other metals more electro-negative than themselves. 
Thus zinc, in contact with precipitated copper, will decompose water at the ordinary 
temperature, hydrogen being evolved, and zinc hydrate separated in white flakes. 



HYDKOGEK 

10. Preparation of hydrogen. — The simplest process, chemically speak- 
ing, for preparing hydrogen in quantity, consists in passing steam over 
red hot iron. An iron tube (A, fig. 9) is filled with iron nails and fixed 




Fig. 9. — Preparation of hydrogen from steam. 



across a furnace (B), in which it is heated to redness by a charcoal fire. 
A current of steam is then passed through it by boiling the water in the 
flask (C), which is connected with the iron tube by a glass tube (D) and 
perforated corks. The hydrogen is collected from the glass tube (G) in 
cylinders (E) filled with water, and inverted in the trough (E) upon the 
bee-hive shelf (H), the first portions being allowed to escape, as containing 
the air in the apparatus. The iron combines with the oxygen of the 
water to form the black oxide of iron (Eeo0 4 ) which will be found in a 



crystalline state upon the surface of the metal, 
represented by the equation — 



The decomposition is 



4H 2 + Fe 3 = Fe 3 4 + H 8 . 

Water. Black oxide of iron. 

The weight of an atom of iron is 56 times that of an atom of hydrogen; 
hence the Fe 3 in the above equation represent 56 x 3, or 168 parts by 
weight of iron. 

The process by which hydrogen is most commonly prepared consists in 
dissolving iron or zinc in a mixture of sulphuric acid and water. 

Zinc is the most convenient metal to employ for the preparation of 
hydrogen in this way. It is used either in small fragments or cuttings, 
or as granulated zinc, prepared by melting it in a ladle and pouring it 
from a height of three or four feet into a pailful of water. The zinc 
is placed in the bottle (A, fig. 10), covered with water to the depth of 



MONATOMIC AND DIATOMIC ELEMENTS. 



15 



two or three inches, and diluted sulphuric acid slowly poured in through 
the funnel tube (B) until a pretty brisk effervescence is observed. The 
hydrogen is unable to escape 
through the funnel tube, 
since the end of it is beneath 
the surface of the water, but 
it passes off through the bent 
tube (C), and is collected 
over water as usual, the first 
portion being rejected as con- 
taining air. 

By allowing the solution 
left in the bottle to cool, 
crystals of zinc sulphate 
{ivhite vitriol) may be ob- 
tained. 

It will be noticed that 
the liquid becomes very hot 
during the action of the acid upon the zinc, the heat being produced by 
the combination which is taking place. The black flakes which separate 
during the solution of the zinc consist of metallic lead, which is always 
present in the zinc of commerce, and much accelerates the evolution 
of hydrogen by causing galvanic action. Pure zinc placed in contact 
with diluted sulphuric acid evolves hydrogen very slowly. 

The preparation of hydrogen by dissolving zinc in diluted sulphuric 
acid may be represented by the equation * 




Fig. 10. — Preparation of hydrogen. 



H 2 S0 4 

Sulphuric acid. 



Zn 



: ZnS0 4 + 

Zinc sulphate. 



H. 



The symbol Zn here represents 1 atom of zinc, which is 65 tines as 
heavy as the atom of hydrogen. An atom of zinc has here displaced 2 
atoms of hydrogen, whereas it was found that an atom of potassium dis- 
placed only 1 atom of hydrogen, which is often expressed by saying that 
potassium is a monatomic element, i.e., is exchangeable for 1 atom of 
hydrogen. 

But since 65 parts of zinc displace 2 parts of hydrogen, zinc is a diatomic 
element, i.e., is exchangeable for 2 atoms of hydrogen. This is commonly 
expressed by writing the symbol of zinc thus — Zn". 

It may be supposed that the atom of a monatomic element, such as hydrogen or 
potassium, exerts its chemical attraction in one direction only, as represented by a 
single line or bond attached to the symbol, thus H - . K - ; whilst a diatomic element, 
such as zinc, exerts chemical attraction in two directions, represented by attaching 
two lines to the symbol, thus-Zn-, or Zn = . Since an atom of oxygen combines 
with two atoms of hydrogen, it must also exert chemical attraction in two directions, 

so that a molecule of water may be represented as H H. The displacement 

of half the hydrogen by potassium (p. 12) then produces K H, caustic 

potash, and the displacement of both atoms of hydrogen by zinc produces Zn= =0, 
or zinc and oxygen united by both their bonds of chemical attraction, forming zinc 
oxide. 



* In this equation the excess of water which must be added to dissolve the zinc sulphate 
is not set down. Hydrogen could not be prepared according to the equation as it stands, 
because the zinc sulphate would collect round the metal and prevent further action. 



16 PROPERTIES OF HYDROGEN. 

Iron might be used instead of zinc, and the solution, when evaporated, 
would then deposit crystals of green vitriol or copperas (sulphate of iron, 
or ferrous sulphate, FeS0 4 ), the action of iron upon the sulphuric acid 
being represented by the equation 

H 2 S0 4 + Fe = FeS0 4 + H 2 , 

Sulphuric acid. Ferrous sulphate. 

which shows that 1 atom (56) of iron has taken the place of 2 atoms of 
hydrogen, and that the iron is diatomic, like zinc. 

Hydrogen has been prepared cheaply in large quantity by heating a mixture of 
slaked lime with anthracite coal in an iron retort ; C + CaO + 2H 2 = CaC0 3 + H 4 . 
On passing steam over the residue ; CaC0 3 = CaO 4- C0 2 : hence, if enough carbon be 
employed in the beginning, large quantities of hydrogen may be obtained by steaming 
and heating alternately. 

11. Physical -properties of hydrogen. — This gas is invisible, and in- 
odorous when pure. The hydrogen obtained by the ordinary methods has 
a very disagreeable smell, caused by the presence of minute quantities of 
compounds of hydrogen with sulphur, arsenic, and carbon ; but the gas 
prepared with pure zinc and sulphuric acid is quite free from smell. It 
is liquefied with extreme difficulty, requiring a pressure of 650 atmo- 
spheres at - 220° F. ( - 140° C). The most remarkable physical property 
of hydrogen is its lightness. It is the lightest of all kinds of matter, 
being about T ^ as heavy as air, and TT X6 2 as nea vy as water. 

The lightness of hydrogen may be demonstrated by many interesting experiments. 
Soap bubbles or small balloons (of collodion, for example) will ascend very rapidly if 
inflated with hydrogen. A light beaker glass may by accurately weighed in a pair 
of scales ; it may then be held with its mouth downwards, and the hydrogen poured 
up into it from another vessel. If it be then replaced upon the scale-pan with its 
mouth downwards, it will be found very much lighter than before. Another form 
of the experiment is represented in fig. 11, where a light glass shade has been sus- 
pended from the balance and counterpoised, the equilibrium being, of course, at once 
disturbed when hydrogen is poured up into the shade. If a stoppered gas jar full 
of hydrogen be held with its mouth downwards, and a piece of smouldering brown 
paper held under it, the smoke, which would rise freely in the air, is quite unable 
to rise through the hydrogen, and remains at the mouth of the jar until the stopper 
is removed, when the hydrogen quickly rises and the smoke follows it. 

12. The employment of hydrogen for filling balloons renders a know- 
ledge of the relation between the weights of equal volumes of hydrogen 
and atmospheric air of great importance. The number expressing this 
relation is termed the Specific Gravity of hydrogen. 

(Definition. — The specific gravity of a gas or vapour is its weight as 
compared with that of an equal volume of some other gas, selected as a 
standard, at the same temperature and pressure.) 

If the weight of a given volume of purified and dried air be repre- 
sented as unity, an equal volume of hydrogen, at the same temperature 
and pressure, would weigh 0*0692, which is expressed by saying that the 
specific gravity of hydrogen (air= 1) is 0'0692. 

In ascertaining the weights of definite volumes of gases, it is of the 
greatest importance that they should have some definite temperature and 
pressure, since the volume of a given weight of gas is augmented by the 
increase of the temperature and by decrease in pressure. In England it is 



UNITS OF GASEOUS VOLUME. 



17 



usual to state the weights of gases at the temperature of 60° on the 
Fahrenheit thermometer, and under a pressure of 30 inches of mercury in 
the barometer, these being regarded as the average conditions of the 
climate. 




Fig. 11. 

On the Continent the standard pressure is very nearly the same, being 
760 millimetres of the barometric column, or 29*922 inches; but the 
standard temperature is that of melting ice ; or 0° on the centigrade scale, 
corresponding to 32° F., a temperature to which gases may be reduced at 
will, by surrounding with melting ice the vessels in which they are 
collected for the purpose of being weighed. 

One grain of hydrogen, at 60° F. and 30 inches Bar., measures 46 "73 
cubic inches. 

Expressed on the Continental system, one gramme (15-43 grains) of 
hydrogen, at 0° C. and 760 mm. Bar., measures 11 "19 litres (one litre = 
61*024 cubic inches = T76 pints). 

It is now easy to calculate how much zinc it would be necessary to dissolve in 
sulphuric acid in order to obtain any desired volume, say 100 cubic feet (172,800 
cubic inches) of hydrogen. Referring to the equation for the preparation of hydro- 
gen, Zn + H 2 S0 4 ==H 2 + ZnS0 4 , and remembering that Zn represents 65 parts by 
weight of zinc, and H 2 represent 2 parts by weight of hydrogen— 



2 grs. H 
93-46 cub. in. 



grs. Zn 
65 



Cub. in. 
172800 



12018 grs. zinc). 



13. It will be observed, in the experiment with the balance (fig. 11), 
that the gas gradually falls out of the jar, notwithstanding its lightness, 
and is replaced by air ; so that, after a time, the equilibrium is restored, 
proving that the molecules of hydrogen possess motion which is independent 
of gravitation. This is evident also from another consideration. The 
total weight of the molecules of hydrogen in one cubic centimetre of 
the gas at 0° C. and 760 mm. Bar. is only -0000896 gramme, and yet its 

B 



18 DIFFUSION OF GASES. 

pressure upon the sides of the vessel containing it amounts to 1033 grammes 
per square centimetre. 

The weight of a single molecule of hydrogen has been calculated to be 
not greater than one ten- thousand-millionth of a gramme, and 21 trillions 
of them are calculated to be contained in one cubic centimetre. This 
enormous number of molecules, moving with great velocity and delivering 
successive blows on the sides of the vessel, give rise to the pressure of 
the gas. 

Hence the pressure of a gas will vary with the weight of its mole- 
cules, and with their velocity. If m be taken to represent the weight 
of a molecule, and v its velocity, mv will express the momentum of each 
molecule ; but the pressure depends not only on the momentum of each 
molecule, but on the number of blows delivered by each molecule in equal 
times, which will increase with the velocity of the molecule. Hence 
mv x v or mv 2 will represent the pressure of the gas. Suppose this pressure 
to be some constant unit of pressure, represented by 1, then mv 2 = 1, and 

v z = — , or v = — T — , 
m Jm 

showing that the velocities of the molecules of gases vary inversely as the 
square roots of their molecular weights. But the molecular weights of 
the gases represent the weights of equal volumes (see p. 3), or the 
specilic gravities of the gases, so that the velocities of the molecules of 
gases vary inversely as the square roots of their specific gravities. 

The absolute velocity of the molecules of a gas may be calculated when 
the pressure, the temperature, and the weight of a given volume of the 
gas are kuown. It has thus been determined that the absolute velocity of 
a molecule of hydrogen at 0° C. and 760 mm. Bar. is 6050 feet per second. 
Oxygen is 1 6 times as heavy as hydrogen, hence the velocity of the oxygen 

molecule, for the same temperature and pressure, would be -j= = — th 

that of the hydrogen molecule, or 1512 feet per second. 

This view of the constitution of gases (known as the kinetic theory, 
from klv7](tl<s, motion) explains their remarkable physical properties. 
If a vessel of hydrogen at 760 mm. pressure were opened into a vacuum, 
the molecules of hydrogen would escape into the vacuum with a velocity 
of 6050 feet per second. If the vessel be opened in air, the velocity of 
the hydrogen molecules will be retarded by collision with the air-molecules, 
but the gas still escapes very rapidly. 

The nitrogen and oxygen gases, which are mixed together in air, being 
respectively 14 and 16 times as heavy as hydrogen, their molecules have 
a lower velocity, and are not carried into the vessel so rapidly as the 
hydrogen passes out. In order to render this evident, the opening 
of the vessel should be closed by some material having very minute 
pores, so as to retard the exchange of the gases, and to measure the relative 
velocities of their molecules, or the rates of diffusion of the gases. 

The diffusion tube (fig. 12) employed for this purpose is a glass tube (A) closed 
at oue end by a plate of plaster of Paris (B). If this tube be filled with hydrogen, * and 

* This tube must be filled by displacement (see fig. 18), in order not to wet the plaster. 
A piece of sheet caoutchouc may be tied over the plaster of Paris, so that dift'usiou may 
not commeuce until it is removed. 



DIFFUSION OF GASES. 



19 



its open end immersed in coloured water, the water will be observed to rise rapidly 
in the tube, on account of the rapid escape of the hydrogen through the pores of the 
plaster. The external air, of course, passes into the tube through the pores at the 
same time, but much less rapidly than the hydrogen passes out, so that the ascent of 
the column of water (C) marks the difference between t, 

the volume of hydrogen which passes out, and that of 
air which passes into the tube in a given time, and 
allows a measurement to be made of the rate of diffusion; 
that is, of the velocity with which the gas issues as 
compared with the velocity with which the air enters, 
this velocity being always taken as unity.* To deter- 
mine the rate of diffusion, it is of course necessary to 
maintain the water at the same level within and without 
the diffusion tube, so as to exclude the influence of 




pressure. 

To prove that the ascent of the hydrogen due to its 
lightness is not instrumental in drawing up the water 
in the diffusion tube, the experiment may be made as 
in fig. 13, where the plate of plaster (o) is turned 
downwards, so that the diffusion is made to take place 
in opposition to the action of gravity. This tube is 
filled by passing hydrogen in through the tube (s), and 
allowing the air to escape through (t), which is afterwards 
closed by a cork. The plaster of Paris (o) is tied over with caoutchouc whilst the 
tube is filled. 

Since the relation between the weights of equal volumes of hydrogen and air is 
that of - 069 : 1, the rates of diffusion will be as 
1 : VO'069 — that is, hydrogen will diffuse about 
3*8 times as rapidly as atmospheric air, or 3*8 
measures of hydrogen will pass out of the diffusion 
tube whilst one measure of air is passing in through 
the plaster. In a similar manner hydrogen would 
escape through minute openings with four times 
the velocity of oxygen ; and laboratory experience 
shows that a cracked jar, or a bottle with a badly 
fitting stopper, may often be used to retain oxygen, 
but not hydrogen. 

A very striking illustration of the high rate of 
diffusion of hydrogen is arranged as represented in 
fig. 14. A is a cylinder of porous earthenware 
(such as are employed in galvanic batteries) closed 
at one end, and furnished at the other with a 
perforated caoutchouc stopper or a cork bung, 
through which passes a glass tube B, about six 

feet long, and half an inch in diameter. The bung is made air-tight by coating it 
with sealing wax dissolved in spirit of wine. This tube being supported so that its 
lower end dips about an inch below the surface of water, a jar of coal-gas is held over 
the porous cylinder, when the velocity of the particles of the gas is manifested by 
their being forced (not only out of the mouth of the jar C, which is open at the 
bottom, but also) through the pores of the earthenware jar, the air from which is 
violently driven out, as if by blowing, through the tube, and is seen bubbling up 
rapidly through the water. When the air has ceased to bubble out, and a large 
volume of gas has entered the porous jar, the bell-jar C is removed, when the gas 
escapes so rapidly through the pores, that a column of twenty to thirty inches 
of water is drawn rapidly up the tube B. If the greatest height to which the water 
ascends be marked, and when it has returned to its former level, a jar of hydrogen 
be held over the porous cylinder, it will be found that the above phenomena are 
manifested in a much higher degree, showing that coal-gas, being heavier than 
hydrogen, does not pass nearly so rapidly through the pores f the earthenware as 
hydrogen does. 




Fi^. 13.— Diffusion tube. 



* Air "being a mixture of nitrogen and oxygen, its rate of diffusion is intermediate 
between the rates of those gases ; however, since the proportions of the gases are very 
nearly constant, no error of any magnitude arises. 



20 



PROPERTIES OF HYDROGEN. 



By connecting the porous cylinder A, by means of a short piece of tube, with a two- 
necked bottle, like that represented in fig. 10, and passing through a cork in the 
other neck, a piece of tube reaching to the bottom of the bottle and drawn out to an 

open point at its upper extremity (fig. 19), water 
may be forced out in a stream of two or three 
feet in height by holding the jar of hydrogen over 
the porous cylinder. 

The great difference in the rates of diffusion of 
hydrogen and oxygen may be easily shown by the 
arrangement represented in fig. 15. A is a jar 
filled with a mixture of two volumes of oxygen 
with one volume of hydrogen, communicating 
through the stop- cock and flexible tube with the 
glass tube B, which is fitted through a perforated 
cork in the bowl of the common tobacco-pipe C, 
the sealing- waxed end of which dips under water 
in the trough D. By opening the stop-cock and 
pressing the jar down in the water, the mixed 
gases may be forced rapidly through the pipe, 
and if a small cylinder (E) be filled with them, 
the mixture will be found to detonate violently 
on the approach of a flame. But if the gas be 
made to pass very slowly through the pipe (at the 
rate of about a cubic inch per minute), the 
hydrogen will diffuse through the pores of the 
pipe so much faster than the oxygen, that the gas 
collected in the cylinder will contain so little 
hydrogen as to be no longer explosive, and to 
exhibit the property of oxygen to rekindle a partly 
extinguished match. 

If two jars of the same size, one made of glass 
and the other of porous earthenware, be filled with 
the explosive mixture by holding them over the 
stop-cock of the jar A, and be then closed with 
glass plates and set aside for a few seconds, it will 
be found that the gas in the earthen jar will 
rekindle a spark on a match, whilst that in the 
glass jar will explode. 

The rapid diffusion of hydrogen through paper 
may be shown by laying a flat piece of filter-paper 
upon the mouth of a cylinder of hydrogen, when 
the gas may be kindled on the upper surface. On 
repeating the experiment with a cylinder of coal- 
gas, only the pale flame of the hydrogen will 
appear above the paper. If a mixture of hydrogen 
and oxygen be employed, the hydrogen will be 
-^S- 14, seen burning before the explosion takes place. 

A cylinder containing 2 vols. H and 1 vol. of 0, if covered with filter-paper, will be~ 
found to contain little else but oxygen after a minute or two. 




14. Chemical properties of hydrogen.- — The most conspicuous chemical 
property of hydrogen is its disposition to burn in air when raised to a 
moderately high temperature, entering into combination with the oxygen 
of the air to form water. The formation of water during the combustion 
of hydrogen gave rise to its name (vSo>p, water). 

Since an atom of oxygen combines with two atoms of hydrogen to form water, the 
gases will not combine unless under the influence of some force, such as heat or elec- 
tricity, to assist in resolving their molecules into the constituent atoms. 

On introducing a taper into an inverted jar of hydrogen (fig. 16), the flame of the 
taper will be extinguished, but the hydrogen will burn with a pale flame at the 
mouth of the jar, and the taper may be rekindled at its flame by slowly withdraw- 
ing it. 



PROPERTIES OF HYDROGEN. 



21 



The lightness and combustibility of hydrogen may be illustrated simultaneously 
by some interesting experiments. If two equal gas cylinders be filled with hydrogen, 
and held with their mouths respectively upwards and downwards, it will be found 
on testing each with a taper after the same interval, that the hydrogen has entirely 
escaped from the cylinder held with its mouth upwards, whilst the other still remains 
nearly filled with gas. 

The hydrogen may be scooped out of the jar A (fig. 17) with the small cylinder B 
attached to a handle. On removing B, and applying a taper to it, the gas will take 
fire. 




Fig. 15. — Separation of hydrogen and oxygen by atmolysis.* 

A cylinder may be filled with hydrogen by displacement of air (fig. 18), if the tube 
from the hydrogen bottle be passed up into it. 





Fig. 16. 



Fig. 17. 




If such a dry cylinder of hydrogen be kindled whilst held with its mouth down- 
wards, the formation of water during the combustion of the hydrogen will be indi- 
cated by the deposition of dew upon the sides of the cylinder. 

* This term has been applied to the separation of gases by diffusion ; cltix6<s, vapour ; 
\<joo, to loosen. 



22 



EXPLOSION OF HYDROGEN AND AIR. 




By softening a piece of glass tube in the flame of a spirit-lamp, drawing it out and 
filing it across in the narrowest part (fig. 19), a jet can be made from which the 
hydrogen may be burnt. This jet may be fitted by a perforated cork to any common 

bottle for containing the zinc 



and sulphuric acid (fig. 20). 

The hydrogen must be allowed 
to escape for some minutes before 
applying a light, because it forms 
an explosive mixture with the 
* 1 S' iy - air contained in the bottle. This 

may be proved, without risk, by placing a little granulated zinc in a soda-water 
bottle, pouring upon it some diluted sulphuric acid, and quickly inserting a perforated 
cork, carrying a piece of glass tube about three inches long, and one-eighth of an inch 
Avide. If this tube be immediately applied to a flame, the mixture of air and hydro- 
gen will explode, and the cork and tube will be projected to a considerable distance. 

By inverting a small test-tube over the jet in fig. 20, a specimen of the hydrogen 
may be collected, and may be kindled, to see if it burns quietly, before lighting 
the jet. 

A dry glass, held over the flame, will collect a considerable quantity of water, 
formed by the combustion of the hydrogen. 

The combustion of hydrogen produces a greater heating effect than that 
of an equal weight of any other combustible body. It has been deter- 
mined that 1 gr. of hydrogen , in the act of combining with 8 grs. of 
oxygen, produces enough heat to raise 62,031 grs. of water from 32° F. 
to 33° ¥. (or 34,462 grs. from 0° C. to 1° C.) The temperature of the 
hydrogen name is probably about 1830° C. Notwithstanding its high 
temperature, the flame of hydrogen is almost devoid of illuminating 
power, on account of the absence of solid particles. 

15. If a taper be held several inches above a cylinder of hydrogen, 
standing with its mouth upwards, the gas will be kindled with a loud 





Fig. 20. 



Fig. 21. 



explosion, because an explosive mixture of hydrogen and air is formed in 
and around the mouth of the cylinder. 

If a stoppered glass jar (fig. 21) be filled with hydrogen, and supported upon three 
blocks, it will be found, if the hydrogen be kindled at the neck of the jar, that it will 
burn quietly until air has entered from below in sufficient proportion to form an 
explosive mixture, which will then explode with a loud report. 

The same experiment may be tried on a smaller scale, with the two-necked copper 
vessel (fig. 22), the lower aperture being opened some few seconds after the hydrogen 
has been kindled at the upper one. 




PROPERTIES OF OXYGEN. 23 

The explosion of the mixture of hydrogen and air is due to the sudden 
expansion caused by the heat generated in the combination of the hydrogen 
with the oxygen throughout the mixture. After 
the explosion of the mixture of hydrogen and air 
(oxygen and nitrogen), the substances present are 
steam (resulting from the combination of the 
hydrogen and oxygen) and nitrogen, which are 
expanded by the heat developed in the combination, 
to a volume far greater than the vessel can contain, 
so that a portion of the gas and vapour issues very 
suddenly into the air around, the collision with 
which produces the report. 

If pure oxygen be substituted for air, the ex- 
plosion will be more violent, because the mixture °" 

is not diluted with the inactive nitrogen. The further study of this 
subject must be preceded by that of oxygen. 

OXYGEN". 

= 16 parts by weight = 1 vol. 16 grains = 46 -7 cub. in. at 60° F. and 30" Bar. 
16 grammes = 11 "2 litres at 0° C. and 760 mm. Bar. 

16. Oxygen is the most abundant of the elementary substances. It con- 
stitutes about one-fifth (by volume) of atmospheric air, where it is merely 
mixed, not combined, with the nitrogen, which composes the bulk of the 
remainder. Water contains eight-ninths (by weight) of oxygen; whilst 
silica and alumina, which compose the greater part of the solid earth (as 
far as we know it), contain about half their weight of oxygen. 

Before inquiring which of these sources will, most conveniently furnish 
pure oxygen, it will be desirable for the student to acquire some know- 
ledge of the properties of this element, and of the chemical relations 
which it bears to other elementary bodies, for without such knowledge it 
will be found very difficult to understand the processes by which oxygen 
is procured. 

17. Physical properties of oxygen. — From the fact of its occurring in an 
uncombined state in the atmosphere, it will be inferred that oxygen is 
perfectly invisible, and without odour. It is liquefied with difficulty, 
requiring a pressure of 320 atmospheres at - 220° F. ( - 140° C.) Oxygen 
gas is a little more than one-tenth heavier than air, which is expressed in 
the statement that its specific gravity is 1*1057. 

In the study of theoretical chemistry, it is expedient to select hydro- 
gen instead of air as the standard with which the specific gravities of 
gases are compared; for, since the atomic weights are also referred to 
h} r drogen as the unit, and the atomic weights represent the weights of 
equal volumes, the numbers expressing the atomic weights of the ele- 
mentary gases are identical with their specific gravities (H = l). Thus 
the specific gravity of oxygen (H = l) is 16. It will be found con- 
venient to remember that the specific gravity of a gas or vapour is the 
weight of one volume. 

18. Chemical properties of oxygen. — This element is remarkable for the 
wide range of its chemical attraction for other elementary bodies, with all 
of which, except one, it is capable of entering into combination. Fluorine 
is the only element which is not known to unite with oxygen. 



24 



COMBUSTION. 



With nearly all the elements oxygen combines in a direct manner ; 
that is without the intervention of any third substance. 

There are only seven elements (among those of practical importance) 
which do not unite in a direct manner with oxygen, viz., chlorine, bromine, 
iodine, fluorine, gold, silver, platinum. 

(Definition. — The compounds of oxygen with other elements are 
called Oxides.) 

The act of combination with oxygen, or oxidation, like all other acts of 
chemical combination, is attended with the development of heat.* When 
the heat thus produced is sufficient to, render the particles of matter 
luminous, the act of combination is styled combustion. 

(Definition.- — Combustion is chemical combination attended with heat 
and light.) 

19. Phosphorus, the only non-metal which combines 'with oxygen at the 
ordinary temperature, affords a good illustration of these propositions. 
This element, a solid at the ordinary temperature, is preserved in bottles 
filled with water, on account of the readiness with which the oxygen of 
the air combines with it. If a small piece of phosphorus be dried by 
gentle pressure between blotting paper, and exposed to the air, its par- 
ticles begin to combine at once with oxygen, and the heat thus developed 
slightly raises the temperature of the mass. 

Now, heat generally encourages chemical union, so that the effect of 
this rise of temperature is to induce a more extensive combination of the 
phosphorus with the oxygen, causing a greater development of heat in a 
given time, until the temperature is sufficient to render the particles 
brilliantly luminous, and a true case of combustion results — the combina- 
tion of the phosphorus with oxygen, attended with production of heat 
and light. 



(Definition. — Combustion 




Fig. 23. 



in air is the chemical combination of the 
elements of the combustible with the 
oxygen of the air, attended with de- 
velopment of heat and light.) 

If a dry glass (fig. 23) be placed over 
the burning phosphorus, the thick 
white smoke which proceeds from it 
may be collected in the form of snowy 

1|= flakes. These flakes are commonly 
termed phosphoric anhydride,^ and 
are composed of 80 parts by weight 
of oxygen, and -62 parts of phos- 
phorus (P 2 5 ). 



If the white flakes are exposed to the air for a short time, they attract 
moisture and become little drops, which have a very sour or acid taste. 
It was mentioned at page 12 that all substances which have such a taste 



* Though this heat is not always perceptible by the thermometer or by the senses. 
Thus, when chalk is dissolved in an acid, no heat is perceived, because all the heat attend- 
ing the union of the lime with the - acid is consumed in converting the carbonic acid from 
the solid chalk into a gas. To explain the manifestation of heat in the act of chemi- 
cal combination falls within the province of the physicist rather than of the chemist. 
Modern writers attribute it to the motion of the molecules which compose the combining 
masses. 

+ A nhydride, or without water, from av, negative, and vSwp, water. 



OXYGEN, 



25 



have been found also to be capable of changing the blue colour of litmus* 
to red, whence the chemist is in the habit of employing paper dyed with 
blue litmus for the recognition of an acid. 

(Definition. — Anhydride, a compound which produces an acid when 
brought into contact with water.) 

For the exact definition of an acid see page 27. 

During the slow combination of phosphorus with the oxygen of the air, 
before actual combustion commences, only 48 parts of oxygen unite with 
62 parts of phosphorus, forming the substance called phosjrfwrous 
anhydride (P o 3 ). 

(Definition. — The endings -ous and -ic distinguish between two com- 
pounds formed by oxygen with the same element ; -ous implying the 
smaller proportion of oxygen.) 

Unless the temperature of the air be rather high, the fragment of phos- 
phorus will not take fire spontaneously, but its combustion may always 
be ensured by exposing a larger surface to the action of the air. As a 
general rule, a fine state of division favours chemical combination, because 
the attractive force inducing combination operates only between sub- 
stances in actual contact ; and the smaller the size of the particles, the 
more completely will this condition be fulfilled. 

Thus if a small fragment of dry phosphorus be placed in a test-tube, and dissolved 
in a little bisulphide, of carbon, the solution when poured upon blotting paper (fig. 
24), will part with the solvent by evapor- 
ation, leaving the phosphorus in a very 
finely divided state upon the surface of 
the paper, where it is so rapidly acted 
on by the oxygen of the air that it bursts -^S^\SPSf^# 
spontaneously into a blaze. ~^^ ^£Wx>' /|r ===i=== f- 

Though the light emitted by 
phosphorus burning in air is very 
brilliant it is greatly increased when lg ' 

pure oxygen is employed ; for since the nitrogen with which the oxygen 
in air is mixed takes no part in the act of combustion, it impedes and 
moderates the action of the oxygen. Each volume- of the latter gas is 
mixed, in air, with four volumes of nitrogen, so that we may suppose 
five times as many particles of oxygen to 
come into contact, in a given time, with 
the particles of the phosphorus immersed 
in the pure gas, which will account for 
the great augmentation of the tempera- 
ture and light of the burning mass. 

To demonstrate the brilliant combustion of 
phosphorus in oxygen, a piece not larger than 
a good-sized pea is placed in a little copper or 
iron cup upon an iron stand (fig. 25), and Fig. 25. 
kindled by being touched with a hot wire (for 
even in pure oxygen spontaneous combustion 
cannot be ensured). The globe, having been previously filled with oxygen, and kept 
in a plate containing a little water, is placed over the burning phosphorus. t 

* A colouring matter prepared from a lichen, Roccella tinctoria ; the cause of the 
change of colour will be more easily understood hereafter. 

f This globe should be of thin, well-annealed glass, and is sure to be broken if too 
large a piece of phosphorus be employed. 





-Phosphorus burning in 
oxygen. 



26 



OXYGEN WITH NON-METALS. 



It will be observed that the same white clouds of phosphoric anhydride 
are formed, whether phosphorus is burnt in oxygen or in air, exemplify- 
ing the fact that a substance will combine with the same proportion of oxygen 
whether its combustion be effected in pure oxygen or in atmospheric air. 
The apparent increase of heat is due to the combustion of a greater weight 
of phosphorus in a given time and space. The total heating effect pro- 
duced by the combustion of a given weight of phosphorus is the same 
whether air or pure oxygen be employed. 

20. Sulphur (brimstone) affords an example of a non-metallic element 
which will not enter into combination with oxygen until its temperature 
has been raised very considerably. When sulphur is heated in air, it 
soon melts ; and as soon as its temperature reaches 500° F. it takes fire, 
burning with a pale blue flame. If the burning sulphur be plunged into 
a jar of oxygen, the blue light will become very brilliant, but the same 
act of combination takes place — 32 parts by weight of oxygen uniting with 
32 parts of sulphur to form sulphurous acid gas (S0 2 ), which may be recog- 
nised in the jar by the well-known suffocating smell of brimstone matches. 
The experiment is most conveniently performed by heating the sulphur 
in a deflagrating spoon (A, fig. 26), which is then plunged into the jar of 

oxygen, its collar (B) resting upon the 
neck of the jar, which stands in a plate 
containing a little water. The water ab- 
sorbs a part of the sulphurous acid gas, 
and will be found capable of strongly red- 
dening litmus paper. It is possible to 
produce, though not by simple combus- 
tion, a compound of sulphur with half 
as much more oxygen (S0 3 sulphuric 
anhydride), showing that a substance does 
not always take up its full share of oxygen 
lohen burnt. 

The luminosity of the flame of sulphur 
is far inferior to that of phosphorus, be- 
cause, in the former case, there are no 




Fig. 26. 



-Sulphur burning in 
oxygen. 

extremely dense particles in the flame corresponding to those of the 
phosphoric oxide produced in the combustion of phosphorus. 

21. Carbon, also a non-metallic element, requires the application of a 
higher temperature than sulphur to induce it to enter into direct union 
with oxygen ; indeed, perfectly pure carbon appears to require a heat 
approaching whiteness to produce this effect. But charcoal (the carbon in 
which is associated with not inconsiderable proportions of hydrogen 
and oxygen) begins to burn in air at a much lower temperature ; and if a 
piece of wood charcoal, with a single spot heated to redness, be lowered 
into a jar of oxygen, the adjacent particles will soon be raised to the 
combining temperature, and the whole mass will glow intensely, 32 parts 
by weight of oxygen uniting with 12 parts of carbon to form carbonic 
acid gas (C0 2 ), which will redden a piece of moistened blue litmus paper 
suspended in "the jar, though much more feebly than either sulphurous or 
phosphoric acid. It should be remembered that carbon is an essential 
constituent of cdl ordinary fuel, and carbonic acid gas is always produced 
by its combustion. 



OXYGEN WITH METALS. 



27 



It will be noticed that the combustion of the charcoal is scarcely 
attended with flame; and when pure carbon (diamond, for example) 
is employed, no flame whatever is produced in its combustion, because 
carbon is not convertible into vapour, and all flame is vapour or gas in the 
act of combustion ; hence, only those substances bitrn with flame which are 
capable of yielding combustible gases or vapours. 

22. The three examples of sulphur, phosphorus, and carbon suffi- 
ciently illustrate the tendency of non-metals to form acids by union with 
oxygen and water, which originally led to the adoption of its name, derived 
from o£u's, acid, and yewdw, I produce. All the non-metallic elements, 
except hydrogen and fluorine, are capable of forming anhydrides by their 
union with oxygen. 

Definition of an acid. — A compound containing hydrogen, which, when 
in contact with an alkali (p. 12) exchanges its hydrogen, or a portion of 
it, for the alkali-metal. 

For example — 



HC1 + 

'drochloric acid. 


NaOH 

Soda. 


= NaCl + 

Sodium chloride. 


H 2 

Water. 


H 2 S0 4 + 

Sulphuric acid. 


2KOH 

Potash. 


= K 2 S0 4 + 

Potassium sulphate. 


2H 2 

Water. 


H 3 P0 4 + 

Phosphoric acid. 


2XaOH 

Soda. 


= Ka 2 HP0 4 + 

Sodium phosphate. 


2H 2 

Water. 



23. The metals, as a class, exhibit a greater disposition to unite directly 
with oxygen, though few of them will do so in their ordinary condition, 
and at the ordinary temperature. Several metals, such as iron and lead, 
are superficially oxidised when exposed to air under ordinary conditions, 
but this would not be the case unless the air contained water and car- 
bonic acid gas, which favour the oxidation in a very decided manner. 
Among the metals which are of importance in practice, five only are 
oxidised by exposure to dry air at the ordinary temperature, viz., potassium, 
sodium, barium, strontium, and calcium, the attraction of these metals for 
oxygen being so powerful that they must be kept under petroleum, or some 
similar liquid free from oxygen. On the other hand, three of the com- 
mon metals, silver, gold, and platinum, have so little attraction for 
oxygen that they cannot be induced to unite with it directly, even at 
high temperatures. 

If a lump of sodium be cut across with a knife, the fresh surfaces will 
exhibit a splendid lustre, but will very speedily tarnish by combining 
with oxygen from the air, which gives rise to a coating of sodium oxide, 
and this to some extent protects the metal beneath from oxidation. The 
freshly cut sodium shines in the dark like phosphorus. Even when the 
attraction of the sodium for oxygen is increased by the application of 
heat, it is long before the mass of sodium is oxidised throughout, unless 
the temperature be sufficiently high to convert a portion of the sodium 
into vapour, which bursts through the crust of oxide, and burns with a 
yellow flame. If the spoon containing the sodium (see fig. 26) be now 
plunged into a jar of oxygen, the yellow flame will be far more brilliant. 

Sixteen parts by weight of oxygen here combine with 46 parts of 
sodium to form disodium oxide (Na. 2 0) ; which remains in the spoon in a 




28 OXYGEN WITH METALS. 

fused state. When the spoon is cool, it may be placed in water, which 
will dissolve the oxide, converting it into the alkali soda, 

Na 2 + H 2 = 2NaHO 

Water. Soda. 

24. Zinc will serve as an example of a metal which has no disposition 
to enter into combination with oxygen at the ordinary temperature,* but 
which is induced to unite with it by a very moderate heat. If a little 
zinc (spelter) be melted in a ladle or crucible, and stirred about with an 
iron rod, it burns with a beautiful greenish flame, produced by the union 

of the vapour of zinc with the oxygen of 
the air. But the combustion is far more 
brilliant if a piece of zinc-foil be made 
into a tassel (fig. 27), gently warmed at 
the end, dipped into a little flowers of 
sulphur, kindled, and let down into a jar 
of oxygen, when the flame of the burning 
sulphur will ignite the zinc, which burns 
with great brilliancy. On withdrawing 
what remains of the tassel after the com- 
bustion is over, it will be found to con- 
Fig. 27. -Zinc burning in oxygen. ^ of ft Mablef masgj wMch hag a fiue 

yellow colour while hot, and becomes white as it cools. This is the zinc 
oxide (ZnO), formed by the union of 16 parts by weight of oxygen with 
65 parts of zinc. 

The zinc oxide does not possess the properties of an acid or an alkali, 
and belongs to another class of compounds termed bases, which are not 
soluble in water as the alkalies are, but, like them, are capable of neutral- 
ising, either partly or entirely, the acids. Thus, if the zinc oxide were 
added to diluted sulphuric acid as long as the acid would dissolve it, the 
well-known corrosive properties of the acid would be destroyed, although it 
would still retain the power of reddening blue litmus, and the solution would 
now contain a new substance, or salt, called zinc sulphate (ZnS0 4 ). 

(Definition. — A base is a compound body which is capable of neutral- 
ising an acid, either partly or entirely.) 

It will be observed that an alkali is only a particular species of base, 
and might be defined as a base which is very soluble in water. 

(Definition. — A. salt is a compound formed when the hydrogen in an 
acid is replaced, either entirely or partly, by a metal; thus, sodium 
chloride, ISTaCl, is formed by the replacement of the H in HC1, hydrochloric 
acid, by sodium ; sodium phosphate, JNa 2 HP0 4 , is formed from phosphoric 
acid, H 3 P0 4 , by the replacement of two-thirds of the hydrogen by sodium.) 

25. Iron, in its ordinary form, like zinc, is not oxidised by dry air or 
oxygen at the ordinary temperature ; but if it be heated even to only 
500° F. a film of oxide of iron forms upon its surface, and as the heat is 
increased the thickness of the film increases, until eventually it becomes so 
thick that it can be detached by hammering the surface, as may be seen 
in a smith's forge. If an iron rod as thick as the little finger be heated 
to whiteness at the extremity, and held before the nozzle of a powerful 

* Unless water and carbonic acid gas be present, as in common air. 
+ Friable, easily crumbled or disintegrated. 



OXIDES. 



29 




Fig. 28 



these 



Watch-spring burning 
in oxygen. 

cases is really a com- 



bellows, it will bum brilliantly, throwing off sparks and dropping melted 
oxide of iron. If a stream of oxygen be substituted for air, the combus- 
tion is of the most brilliant description. A watch-spring (iron combined 
with about 1 per cent, of carbon) may be 
easily made to burn in oxygen by heating 
it in a flame till its elasticity is destroyed, 
and coiling it into a spiral (A, fig. 28), one 
end of which is fixed, by means of a cork, 
in the deflagrating collar B ; if the other 
end be filed thin and clean, dipped into a 
little sulphur, kindled and immersed in a 
jar of oxygen (C) standing in a plate of 
water, the burning sulphur will raise the 
iron to the point of combustion, and the 
spring will be converted into molten drops 
of oxide. 

The black oxide of iron formed in all 
bination of two distinct oxides of iron, one of which contains 16 parts by 
weight of oxygen and 56 parts of iron, and would be written FeO, whilst 
the other contains 48 parts of oxygen and 112 parts of iron, expressed by 
the formula Fe 2 3 . To distinguish them, the former is usually called 
protoxide of iron (7rpurros, first) or ferrous oxide, and the latter sesquioxide 
(in allusion to the ratio of one and a half to one between the oxygen and 
the metal) or ferric oxide, The sesquioxide of iron combined with water 
constitutes ordinary rust. 

The black oxide usually contains one combining weight of each oxide, 
so that it would be written FeO.Fe 2 3 , or Fe 3 4 . It is powerfully 
attracted by the magnet, and is often called magnetic oxide of iron. The 
abundant magnetic ore of iron, of which the loadstone is a variety, has a 
similar composition. 

Iron in a very fine state of division will take fire spontaneously in air 
as certainly as phosphorus. Pyrophoric iron can be obtained (by a process 
to be described hereafter) as a black powder, which must be preserved in 
sealed tubes. When the tube is opened, and its contents thrown into the 
air, oxidation takes place, and is attended with a vivid glow. In this 
case the red sesquioxide of iron is produced instead of the black oxide. 

Both these oxides of iron are capable of neutralising, or partly neu- 
tralising, acids, and are, therefore, basic oxides or bases, like the oxides of 
zinc and sodium obtained in previous experiments. So general is the 
disposition of metals to form oxides of this class, that it may be regarded 
as one of the distinguishing features of a metal, for no non-metal ever 
forms a base with oxygen. 

(Definition. — A metal is an element capable of forming a base* by 
combining with oxygen.) 

Many metals are capable also of forming anhydrides with oxygen ; 
thus, tin forms stannic anhydride (Sn0 2 ), antimony forms antimonic anhy- 
dride (Sb 2 5 ), and it is always found that the anhydride of a metal con- 
tains a larger proportion of oxygen than any of the other oxides which 
the metal may happen to form. 

26. There is a third class of oxides, termed the indifferent oxides, be- 

* The metal tungsten appears at present to be an exception to this rule, no well-defined 
basic oxide of this metal being known. 



10 



PREPARATION OF OXYGEN. 



cause they are neither anhydrides nor bases ; such oxides may be formed 
either by non-metals or metals ; thus water (H 2 0), the oxide of hydrogen, 
is an indifferent oxide, and the black oxide or binoxide of manganese 
(Mn0 2 ) is an example of an indifferent metallic oxide. 

27. Preparation of Oxygen. — For almost all the useful arts in which 
un combined oxygen is required, the diluted gas contained in atmospheric 
air is sufficient, since the nitrogen mixed with it does not interfere with 
its action. 

From atmospheric air pure oxygen* was first obtained by Lavoisier towards 
the end of the last century. His process is far too tedious to be employed 
as a general method of preparing oxygen, but it affords a very good example 
of the relation of heat to chemical attraction. Some mercury was poured 
into a glass flask with a long narrow neck, which was placed on a 
furnace, so that its temperature might be constantly maintained at about 
660° F. for twelve days. The mercury boiled, and a portion of it was 
converted into vapour, which condensed in the neck of the flask and ran 
back again. Eventually part of the mercury was converted into a red 
powder, having combined with the oxygen of the air (or undergone oxida- 
tion) to form the red oxide of mercury. The nitrogen of the air does not 
enter into combination with the mercury. 

By heating this oxide of mercury to a temperature approaching a red 
heat (about 1000° F.) it is decomposed into mercury and oxygen gas 
(HgO = Hg + 0). 

It is very generally found, as in this instance, that heat of moderate 
intensity will favour the operation of chemical attraction, whilst a more 
intense heat will annul it. 




Fig. 29. — Preparation of oxygen from oxide of mercury. 

For the purpose of experimental demonstration, the decomposition of the oxide of 
mercury may be conveniently effected in the apparatus represented by fig. 29, where 
the oxide is placed in the German glass tube A, and heated by the Bunsen's gas- 
burner B, the metallic mercury being condensed in the bend C, and the oxygen gas 
collected in the gas cylinder D, filled with water, and standing upon the bee-hive 
shelf of the pneumatic trough E. It may be identified by its property of kindling into 
flame the spark left at the end of a wooden match. If the heat be continued for a 
sufficient length of time, the whole of the oxide of mercury will disappear, being 
resolved into its elements. In technical language, the mercury is said to be reduced. 

Upon the first application of heat the red oxide suffers a physical change, in 
consequence of which it becomes black ; but its red colour returns again if it be 
allowed to cool. 

A much cheaper process for obtaining unmixed oxygen from the air is 
now employed upon the large scale. It depends upon the principle that 
the oxides of manganese, when heated in contact with alkalies and air, 



EXTRACTION OF OXYGEN FROM AIR. 



31 



are capable of absorbing the oxygen from trie air, and of subsequently 
giving it up again if heated in a current of steam. 

To illustrate this process, about four ounces of dry sodium manganate (which may 
be purchased cheaply in a crude state) are introduced into a porcelain tube* (t, fig. 30) 
fixed in a furnace. One end of the tube is connected with a two-branched glass tube, 
so that either a current of air may be passed through it by the tube a, or a current of 
steam from the flask w. On heating the manganate in the tube to dull redness, and 
passing the steam over it, oxygen is evolved, and may be collected in the jar o. 

2Na 2 Mn0 4 + 2H 2 = 4XaHO + Mn,0 3 + 3 

Sodium c tt d Sesquioxide of 

manganate. manganese. 

If the current of steam be discontinued and the air be slowly passed through the 
tube a, the oxygen of the air will be absorbed, and its nitrogen may be collected in 
the jar n. 

4XaHO + Mn 2 3 + 3(0 + X 4 ) = 2Na 2 Mn0 4 + 2H 2 + X 12 . 
Air. 

If the proper temperature be employed, the stream of gas issuing from the tube 
may be constantly kept up, and may be made to consist of oxygen or nitrogen 
accordingly as steam or air is passed through the tube. The current of air is regu- 
lated by the nipper-tab c. 

The gas-furnace represented in fig. 30 consists of a row of twelve Bunsen burners, 




Fig. 30. — Extraction of oxygen from air. 

each having a stop-cock by which the flame is regulated. The horizontal pipe b, 
from which they spring, is capable of being raised or lowered at pleasure. The 
porcelain tube t is laid in a semi-cylindrical trough made of stout iron rods, and 
filled with pieces of pumice-stone or fire-brick. Above this is placed a corresponding- 
trough, so that the tube is entirely surrounded by glowing material. t The heat 
must be applied gradually to avoid splitting the tube. 

28. The only other natural source from which it has been found con- 
venient to prepare pure oxygen, is a black mineral composed of manganese 
and oxygen. It is found in some parts of England, but much more 
abundantly in Germany and Spain, whence it is imported for the use of 

* A copper tube with screw-caps, into which narrow brass or copper tubes are brazed, 
may be advantageously substituted for the porcelain tube. The process is much facilitated 
by mixing the manganate of soda with an equal weight of oxide of copper. 

*f* This burner, as well as the burner described at page 10, was constructed-for me by Mr. 
Rowley, formerly of the Royal Military Academy, Woolwich, whose readiness in perceiving 
the intention of an apparatus, and in improving upon the original idea as the work pro- 
ceeded, rendered his co-operation in arranging experimental illustrations of the greatest 
service to me 



32 



PREPARATION OF OXYGEN. 



the bleacher and glass-maker. Its commercial name is manganese, but it 
is known to chemists as binoxide of manganese or manganese dioxide 
(Mn0 2 ), and to mineralogists by several names designating different 
varieties. The most significant of these names is pyrolusite, referring to 
the facility with which it may be decomposed by heat (7rvp, fire, and 
\vo), to loosen). 

One of the cheapest methods of preparing oxygen consists in heating 
small fragments of this black oxide of manganese in an iron retort, placed 
in a good fire, the gas being collected in jars filled with water, and stand- 
ing upon the shelf of the pneumatic trough, or in a gas-holder or gas-bag, 
if large quantities are required. 

The attraction existing between manganese and oxygen is too powerful 
to allow the metal to part with the whole of its oxygen when heated, so 
that only one-third of the oxygen is given off in the form of gas, a brown 
oxide of manganese being left in the retort." 55 * 



29. By far the most convenient source of oxygen, for general use in the 
laboratory, is the artificial salt called chlorate of potash, or potassium 

chlorate, which is largely manufactured 
for fireworks, percussion-cap composi- 
tion, &c. If a few crystals of this 
salt be heated in a test-tube over a 
spirit-lamp (fig. 31), it soon melts to a 
clear liquid, which presently begins to 
boil from the disengagement of bubbles 
of oxygen, easily recognised by intro- 
ducing a match with a spark at the end 
into the upper part of the tube. If 
the action of heat be continued until no 
more oxygen is given off, the residue 
in the tube will be the salt termed 
potassium chloride, 




Fig. 31. 



KC10 3 = KC1 + 

Potassium chlorate. Potassium chloride. 



o 3 . 



To ascertain what quantity of oxygen would be furnished by a given weight of 
the chlorate, the combining weights must be brought into use. Referring to the 
table of atomic weights, it is found that K = 39, = 16, and CI = 35 '5; hence the 
molecular weight of chlorate of potash is easily calculated. 

One atomic weight of potassiuum, . . 39 

,, ,, chlorine, . . 35 '5 

Three atomic weights of oxygen, . .48 



So that 122 "5 grains of chlorate would yield 48 grains of oxygen. 

Since 16 grains of oxygen measure 467 cubic inches (p. 23) the'48 grs. will measure 
140 cubic inches. 

Hence it is found that 122 '5 grains of potassium chlorate would give 140 cubic 
inches of oxygen measured at 60° F. and 30 in. Bar. 

If one gallon (277*276 cubic inches) of oxygen be required, 212 '6 grains of chlorate 
must be used, or rather more than half an ounce. 



Expressed in the form of an equation 



3Mn0 2 

Black oxide of 

manganese. 



Mn 3 4 + 
Brown oxide of 
manganese. 



2 . 



WATER. 



33 



Since the complete decomposition of the potassium chlorate alone re- 
quires a more intense heat than a glass vessel will usually endure, it is 
customary in preparing oxygen for chemical purposes to facilitate the 
decomposition of the chlorate by mixing it with about one-fifth of its 
weight of powdered black oxide of manganese, when the whole of the 
oxygen is given off at a comparatively low temperature, though the oxide 
of manganese itself suffers no change, and its action has not yet received 
any explanation which is quite satisfactory. 

Fig. 32 shows a very convenient arrangement for preparing and collecting oxygen 
for the purpose of demonstrating its relations to combustion. A is a Florence flask, 




Fig. 32. — Preparation of oxygen. 

in which the glass tube B is fixed by a perforated cork. C is a tube of vulcanised 
india-rubber. The gas-jar is filled with water, and supported upon a bee-hive shelf 
made of earthenware. If pint gas-jars be employed, 300 grains of the chlorate of 
potash, mixed with 60 grains of binoxide of manganese, will furnisli a sufficient 
supply of gas for the ordinary experiments. The binoxide of manganese should be 
thoroughly dried by moderately heating it in a crucible before being mixed with the 
chlorate of potash. It is also advisable to test it by heating a little of it with the 
chlorate, since charcoal and sulphuret of antimony, which form very explosive mix- 
tures with chlorate of potash, have sometimes been sold by mistake for binoxide of 
manganese. The heat must be moderated according to the rate at which the gas is 
evolved, and the tube C must be taken out of the water before the lamp is removed, 
or the contraction of the gas in cooling will suck the water back into the flask. The 
first jar of gas will contain the air with which the flask was filled at the commence- 
ment of the experiment. The oxygen obtained will have a slight smell of chlorine. 



WATER. 

30. Synthesis of Water from its elements. — It has been seen already 
(p. 22) that the combination of hydrogen with oxygen to form water is 
attended with great evolution of heat and consequent expansion, and 
hence the mixture of these gases is found to explode violently on contact 
with flame. 

The experiment may be made safely in a soda-water bottle. The bottle is filled 
with water, and inverted with its mouth beneath the surface of the water ; enough 
oxygen is then passed up into it to fill one-third of its volume ; if the remainder of 
the water be then displaced by hydrogen, and the mouth of the bottle be presented 
to the flame of a spirit-lamp, a very violent explosion will result, attended with a 
vivid blue flash in the bottle. If the mouth of the bottle be presented towards a 
screen of paper, at a distance of 20 or 30 inches, the paper will be violently torn to 
pieces, bearing witness to the concussion between the expanded steam issuing from 
the bottle and the external air. 

C 



34 



SYNTHESIS OF WATER. 



If some of the mixture of oxygen with twice its volume of hydrogen be introduced 
into a capped jar (fig. 33), provided with a piece of caoutchouc tubing and a small 
glass tube, and pressed down in a trough of water, soap-bubbles may be inflated with 
it, which will ascend rapidly in the air, and explode violently when touched with a 
flame, which must not, of course, be applied to the bubble until it is at some distance 
away from the tube, for fear of exploding the mixture in the jar. 




Fig. 33. 

31. In order to demonstrate the production of water in the explosion, the Caven- 
dish eudiometer * (fig. 34) is employed. This is a strong glass vessel, with a stopper 
firmly secured by a clamp (A), and provided with two platinum wires (P), which pass 
through the stopper, and approach very near to each other within the eudiometer, so 





Fig. 34. Fig. 35. 

that the electric spark may easily be passed between them. By screwing the stop- 
cock B into the plate of an air-pump, the eudiometer may be exhausted. It is then 
screwed on to the jar represented in fig. 35, which contains a mixture of two measures 
of hydrogen with one measure of oxygen, standing over water. On opening the stop- 
cocks between the two vessels, the eudiometer becomes filled with the mixture, and 
the quantity which has entered is indicated by the rise of the water in the jar. The 
glass stop-cock C having been closed to prevent the brass cap from being forced oil' 
by the explosion, the eudiometer is again screwed on to its foot, and an electric spark 
passed between the platinum wires, either from a Leyden jar or an induction coil, 
when the two gases will combine with a vivid flash of light, f attended with a very 

* So named from ev&io<s, fine or clear, and /meTpov, a measure, because an instrument 
upon the same principle has been used to determine the degree of purity of the atmosphere. 
The eudiometer was emyloyed by Cavendish about the year 1770, for the synthesis of water. 

*t* Since the steam produced at the moment of combination is here prevented from expand- 
ing, the heat which would have expanded it is saved, so that the temperature is higher 
and the flash of light brighter than when the combination is effected in an open vessel. 



SYNTHESIS OF WATER. 



35 



slight concussion, since there is no collision with the external air. For an instant 
a mist is perceived within the eudiometer, which condenses into fine drops of dew, 
consisting of the water formed by the combination of the gases, which was here 
induced by the high temperature of the electric spark, as it Avas in the former experi- 
ment by the high temperature of the flame. If the gases have been mixed in the 
exact proportion of two measures of hydrogen to one measure of oxygen, the eudio- 
meter will now be again vacuous, and if it be screwed on to the capped jar, may be 
filled a second time with the mixture, which may be exploded in the same manner. 

The entire disappearance of the gases may be rendered obvious to the eye by 
exploding the mixture over mercury. For this purpose the mixed gases should be 
collected from water itself, which is strongly acidified with sulphuric acid, and 
decomposed in the voltameter (A, fig. 36) by the aid of five or six cells of Grove's 
battery. The voltameter contains two platinum plates (B), attached to the platinum 
wires C and D, which are connected with the opposite poles of the battery. The 
first few bubbles of the mixture of hydrogen and oxygen evolved having been allowed 
to escape, in order to displace the air, the gas may be collected in the small eudio- 
meter (E), which has been previously filled with water. This eudiometer is a cylinder 




Fig. 36. — Detonating gas collected from voltameter. 

of very thick glass,* closed at one end, and having two stout platinum wires cemented 
into holes drilled near the closed end, the wires approaching sufficiently near to each 
other to allow the passage of the electric spark. Having been filled with the mixture 
of hydrogen and oxygen from the voltameter, the eudiometer is closed with the finger, 
and transferred to a basin containing mercury, where it is pressed firmly down upon 
a stout cushion of india-rubber, and the spark passed through the mixed gases, 
either from the coil or the Leyden jar. The combustion takes place with violent 
concussion, but without noise ; and since the eudiometer is vacuous after the gases 
have combined, the cushion will be found to be very firmly pressed against its open 
end. On loosening the cushion, the mercury will be violently forced up into the 
eudiometer, which will be completely filled with it, proving that when an electric 
spark is passed through the mixture of 2 volumes of hydrogen and 1 volume of 
oxygen, no residue of gas remains, t 

32. The knowledge of the volumes in which hydrogen and oxygen 
combine, is turned to account in the analysis of gases, to ascertain the 
proportion of hydrogen or oxygen contained in them. Suppose, for 
example, it be required to determine the amount of oxygen in a sample 
of atmospheric air ; the latter is mixed with hydrogen, in more than suffi- 
cient quantity to combine with the largest proportion of oxygen which 

* The bore of the eudiometer should be about half an inch in diameter, and the thick- 
ness of its sides about fths of an inch ; its length is 7 inches. 

t This fact may also be demonstrated with the siphon eudiometer, shown in fig. 37, by 
confining about a cubic inch of the explosive mixture in the closed limb, over water, and 
stopping the open limb securely with a cork, so as to leave a space filled with air between 
the cork and the water. The eudiometer must be very firmly fixed on a stand, or it will 
be broken by the concussion. After it has been proved, it may be held in the hand, as 
in the figure. By firing mixtures of hydrogen and oxygen, in different proportions, in the 
same manner, it may be shown that any excess of either gas above the ratio of 2H : will 
remain uncombined after the explosion. Care is required in these experiments, since 
eudiometers are often burst by the explosion of the mixture of 2 volumes of hydrogen with 
1 volume of oxygen. 



36 



EUDIOMETPJC ANALYSIS OF AIR. 



could be present, and when the combination has been induced by the 
electric spark, the volume of gas which has disappeared (2 volumes H + 1 
volume 0) has only to be divided by three to give the volume of the 
oxygen. 

A bent eudiometer (fig. 37) is generally employed for this purpose. Having been 
completely filled with water, it is inverted in the trough, and the specimen of air is 
introduced, (say 0'5 cubic inch). The open limb is then closed by the thumb, and 
the eudiometer turned so as to transfer the air to the closed 
limb. A stout glass rod is thrust down the open limb, so 
as to displace enough water to equalise the level in both 
limbs, in order that the volume of the air may not be 
diminished by the pressure of a higher column of water in 
the open limb. The volume of the included air having been 
accurately noted, the open limb of the tube is again filled 
up with water, inverted in the trough, and a quantity of 
hydrogen introduced, equal to about half the volume of the 
air. This having been transferred, as before, to the closed 
limb, the columns of water are again equalised, and the 
volume of the mixture of air and hydrogen ascertained. 
The open limb is now firmly closed with the thumb and 
the electric spark passed through the mixture, either from 
the Leydeu jar or the induction-coil. On removing the 
thumb, after the explosion, the volume of gas in the closed limb will be found to have 
diminished very considerably. Enough water is poured into the open limb to 
equalise the level, and the volume of gas is observed. If this volume be subtracted 
from the volume before explosion, the volume of gas which has disappeared will be 
ascertained, and one-third of this will represent the oxygen, which has condensed 
with twice its volume of hydrogen into the form of water. Thus the numbers 
recorded will be — 




Fig. 37. 
Siphon eudiometer. 



Volume of air analysed, 

Volume of air mixed with hydrogen, 
After explosion, 

Difference ) 
(fHandJO) J • 

•30, divided by three = 



0'50 cub. in. 

075 „ 
0'45 ,, 

•30 ,, 



10 cub. in. of oxygen. 



In exact experiments, a correction would be required for any variation of 
the temperature or barometric pressure during the progress of the analysis. 

33. It will have been observed, in the experiment upon the synthesis 
of water in the Cavendish eudiometer, that the volume of water obtained 
is very small in comparison with that of the gases before combination 
nearly 2600 volumes of the mixed gases being required to form 1 volume 
of the liquid. But it is evident that no comparison, can, with propriety, 
be made between the volume of a compound, in the liquid or solid state, 
and that of its components in the gaseous state, since the particles of 
the former are under the influence of the cohesive force from which those 
of the latter are free. For the purposes of such a comparison the volume 
of the compound body must be taken under precisely the same physical 
conditions as the volume of its components. 

If the mixture of hydrogen arid oxygen be measured and exploded at 
or above the boiling-point" of water, it is found that the steam produced 
occupies two-thirds of the volume of the mixed gases, measured at the 
same temperature and atmospheric pressure. Hence, two volumes of 
hydrogen combine with one volume of oxygen to form two volumes of 
aqueous vapour, at the same temperature and pressure. 



SYNTHESIS OF WATER. 



•37 



The combination of hydrogen and oxygen in a vessel heated above 
the boiling-point of water is effected in the apparatus contrived by Dr. 
Hofmann, and represented in fig. 38, where the closed limb of the eudio- 
meter is surrounded by a tube through which the vapour of boiling 
f ousel oil, having a temperature of 270° F., is passed from a flask con- 
nected with the wide tube by a cork and a short wide piece of bent glass 
tubing, jacketed with caoutchouc 
to prevent loss of heat. The 
vapour of fousel oil passes out 
of the wide tube, through the 
tube t which enters the cork at 
the bottom, and conducts the 
vapour into a glass worm (w) im- 
mersed in a jar through which 
cold water is allowed to flow, as 
shown by the arrows. The closed 
limb of the eudiometer having 
been filled with mercury, a small 
quantity of the mixture of hydro- 
gen and oxygen obtained from 
the voltameter (fig. 36) is intro- 
duced into it through a tube 
passed down the open limb, the 
displaced mercury being run out 
through the tube c, which is 
closed by a nipper-tap. The 
closed limb is then heated by the 
vapour, and the mercuiy in the 
two limbs levelled from time to 
time by running a little out 
through c, until the gas in the closed limb no longer expands. Its volume- 
is then observed, an inch more mercury poured into the open limb, which 
is then tightly closed by a cork, and the spark from the induction-coil 
(fig. 6) is passed by the wires - and +. After the explosion the cork 
is removed, and the mercury levelled in the two limbs, when the volume 
of the steam will be found to be just two-thirds of the volume of the gas 
before the explosion. On cooling down, the steam condenses, and the 
mercury entirely fills the closed limb of the eudiometer. 

The experiment may be made at the boiling-point of water, by intro- 
ducing water instead of fousel oil into the flask. The condensing 
apparatus may then be dispensed with, and the tube t left open to the air. 

That 2 volumes of steam should contain 2 volumes of hydrogen and 
1 volume of oxygen would appear, on physical grounds, impossible, since 
two bodies cannot occupy the same space at the same time ; but it must 
be remembered that the two bodies in question have lost their indi- 
viduality in consequence of their chemical combination, by which they 
have become one body — water. 

34. The synthesis of water by weight cannot be effected with accuracy 
by weighing the gases themselves, on account of their large volume. It is 
therefore accomplished by passing an indefinite quantity of hydrogen over 
a known weight of pure hot oxide of copper, when the hydrogen combines. 




Fig. 38.— Synthesis of water above 212 c 



38 



RECIPROCAL COMBUSTION. 



with the oxygen of the oxide to form water. The loss of weight suffered, 
by the oxide of copper gives the amount of oxygen ; and if this be deducted 
from the weight of the water, that of the hydrogen will be ascertained. 

The apparatus employed for this purpose is represented in fig. 39. h is the bottle 
in which hydrogen is generated from diluted sulphuric acid and zinc ; the gas passes 
in 2> through solution of potash, which absorbs any sulphuretted hydrogen ; then 
through s, containing pumice-stone (used on account of its porous character), saturated 
with a strong solution of nitrate of silver, which removes arsenic and antimony from 
the hydrogen ; the gas then passes through vv, containing pumice saturated with oil 




Fig. 39. — Synthesis of water by weight. 

of vitriol to absorb moisture. The bulb c, with the oxide of copper, is weighed before 
and after the experiment, as are the globe g, for condensing the water, and the tube 
t, containing pumice and oil of vitriol, to absorb the aqueous vapour. Of course, the 
bulb c must not be heated until the hydrogen has displaced all the air from the 
apparatus. 

35. It is evident that, although hydrogen is generally designated the 
combustible gas, and oxygen the supporter of combustion, the application of 
these terms depends entirely upon circumstances, since the phenomenon 
of combustion is a repicrocal operation in which both elements have an 
equal share. 

This may be illustrated by a simple experiment. The hydrogen and oxygen reser- 
voirs,* H and 0, fig. 40, are connected with two bent glass tubes passing through a 

cork into an ordinary lamp glass e, 
upon the upper opening of which a 
piece of tin-plate is laid. In order to 
prevent the ends of the glass tubes from 
being fused by the burning gases, little 
platinum tubes, made by rolling up 
pieces of platinum foil, are placed in 
the orifices, and the glass is melted 
round them by the blowpipe flame. 
The hydrogen being lighted, and the 
oxygen turned on to about the same 
extent, the lamp-glass is placed over 
the cork, when the hydrogen burns 
steadily. If the oxygen be slowly 
turned off, the flame will gradually 
leave the hydrogen tube and come over 
to the oxygen, which will continue 
burning in the atmosphere of hydrogen. 
By again turning on the oxygen, the 
_. _ . . , flame may be sent over to the hvdrogen 

Fig. 40.— Reciprocal combustion. tube> With a little care th * e flanie 

may be made to occupy an intermediate position between the two burners, and to 
leap from one to the other at pleasure. 

* These are the wrought-iron vessels in which hydrogen and oxygen are condensed under 
the pressure of a few atmospheres by Mr. Orchard of Kensington. They are far more con- 
venient than gas-bags or gas-holders. 




OXYHYDROGEN BLOWPIPE. 



39 




36. The great energy with which hydrogen combines with oxygen is 
turned to account for the purpose of producing the highest temperature 
which can be obtained by any chemical process. 

The oxyhydrogen blowpipe (fig. 41) is an apparatus for burning a jet of hydrogen 
mixed with half its volume of oxygen. The gases are supplied from separate gas- 
holders (or bags with pressure-boards and weights) 
through the tubes H and 0, which conduct them 
into the brass sphere B. Each of these tubes is 
provided with a valve of oiled silk opening out- 
wards, so as to prevent the passage of either gas 
into the receptacle containing the other. The tube 
A is stuffed with thin copper wires, which would 
rapidly conduct away the heat and extinguish 
the flame of the mixed gases burning at the jet, 
should it tend to pass back and ignite the mixture 
in B. The stop-cocks D and E allow the flow of 
the gases to be regulated so that they may mix in 
the right proportions. If the hydrogen be kindled 
first, it will be found that as soon as the oxygen 
is turned on, the flame is reduced to a very much T 4 1. -Oxyhydrogen blowpipe, 
smaller volume, because the undiluted oxygen & J J ° r r 

required to maintain it occupies only one-fifth of the volume of the atmospheric air, 
from which the hydrogen was at first supplied with oxygen. The heat developed by 
the combustion being therefore distributed over a much smaller area, the temperature 
at any given point of the flame must be much higher, and very few substances are 
capable of enduring it without fusion.* Lime is one of these; and if a cylinder of 
lime be supported, as at L (fig. 41), in the focus of the flame, its particles become 
heated to incandescence, and a light is obtained which is visible at night from very 
great distances, so as to be well adapted for signalling and light-houses. For such 
purposes coal-gas is often used instead of hydrogen [oxycalcium light). 

If a shallow cavity be scooped in a lump of 
quicklime, a few scraps of platinum placed in it, 
and exposed to the oxyhydrogen flame (fig. 42), a 
fused globule of platinum of very considerable size 
may be obtained in a few seconds. By employiug 
a little furnace made of lime, Deville has succeeded 
in fusing platinum in quantities sufficient to cast 
large ingots, a result unattainable by any other 
furnace. Pipeclay, which resists the action of all *&• ' 

ordinary furnace-heats, may be fused into a glass in this flame, whilst gold and silver 
are instantaneously melted, and vaporised into a dense smoke." 

37. In its chemical relations to other elements, hydrogen is diametri- 
cally opposed to oxygen. Whereas the latter combines directly with the 
greater number of the elements, hydrogen will enter into direct combina- 
tion with very few ; oxygen, chlorine, bromine, iodine, carbon, and sulphur 
(the three last with difficulty) are the only elements which unite in a 
direct manner with hydrogen, and of these only chlorine and bromine 
combine with hydrogen at the ordinary temperature, though not without 
exposure to light. Again, whilst fluorine is not known to form any com- 
pound with oxygen, its combination with hydrogen (hydrofluoric acid) is 
one of the most stable compounds known, and it may be safely asserted 
that fluorine in the free state would combine with hydrogen even more 
readily than chlorine does. All the metals form compounds with oxygen, 
but very few combinations of metals with hydrogen have been obtained. 
Indeed, in its relations to other elements, hydrogen closely resembles the 
metals, though it does not fall within the definition of a metal given 




The temperature of this flame has been estimated at about 3000° C 



40 SOLUTION AND CRYSTALLISATION. 

above, since it does not form a base with oxygen, and its combinations 
with the salt-radicals (chlorine, &c.) are acids, and not salts, as is the case 
with metals. 

In the course of some experiments upon the power possessed by metals 
of absorbing (or occluding) gases at high temperatures, and retaining them 
after cooling, Graham found that the metal palladium could be made to 
absorb nearly one thousand times its volume of hydrogen at the tempera- 
ture of boiling water. Finding that the metallic characters of the palla- 
dium were not destroyed, as would be the case if it had combined with a 
non-metallic substance, Graham was inclined to believe in the metallic 
character of hydrogen, or hydrogenium, as he termed it. But since the 
hydrogen is very easily recovered by moderately heating the palladium, 
and the absorption of large volumes of gases by solid bodies, without 
alteration in the properties of the latter, is not at all uncommon, the con- 
clusion is scarcely justified.* The hydrogen associated with palladium, 
how T ever, has far more active properties than ordinary hydrogen, for it 
often combines spontaneously with the oxygen of the air, and will unite 
with chlorine and iodine even in the dark. 

38. Chemical Relations of Water to other Substances.- — In its 
chemical relations water presents this very remarkable feature, that 
although it is an indifferent oxide, its combining tendencies extend over 
a wider range than those of any other compound. Its combinations with 
other substances are generally called hydrates. Water combines with 
two of the elementary substances, viz., chlorine and bromine, forming an 
exception to the general rule, that combination does not take place between 
elementary and compound bodies. ~No other element is even dissolved by 
water in any considerable quantity. One part of iodine is dissolved by 
500 parts of cold water, but no chemical combination appears to take 
place. Oxygen, hydrogen, and nitrogen are dissolved by water in very 
small quantity, but become only mechanically diffused through it, and 
do not enter into chemical combination. 

When water acts upon a compound body, it may either effect a simple 
solution, or may enter into chemical combination with it. 

Simple solution appears to be a purely physical phenomenon not 
accompanied, of necessity, by any chemical action. The dissolved sub- 
stance, iii such cases, is otherwise unchanged in properties, and there is 
no manifestation of heat, as in cases of chemical combination. On the 
contrary, there is a redaction of temperature, such as is always noticed in 
the merely physical change from the solid to the liquid form. Tor 
example, common saltpetre (nitre or nitrate of potash), when shaken with 
water, is rapidly dissolved, the water becoming sensibly colder. If fresh 
portions of saltpetre be added till the water is unable to dissolve any 
more, it will be found that 1000 grs. of water (at 60° ~F.) have dissolved 
about 300 grs. of saltpetre. Such a solution would be called a cold satu- 
rated solution of saltpetre. If the solution be set aside in an open vessel, 
the water will slowly pass off in vapour, and the saltpetre w T ill be gradually 
deposited, its particles arranging themselves in the regular geometrical 
shape of the six-sided prism; which is its common crystalline form. The 
crystals of saltpetre do not contain any water : they are anhydrous. 

* On the other hand, recent experiments have indicated the formation of a compound of 
1 atom of hydrogen with 2 atoms of palladium. The compounds K 2 H and Na 2 H have 
also been examined; the density of the H in all three compounds is found to be - 62. 



SUPERSATURATED SOLUTIONS. 



41 



If saltpetre be added to boiling water (in a porcelain evaporating dish, 
fig. 43), and stirred (with a glass rod) until the water refuses to dissolve 
any more, 1000 grs. of water will be found to have dissolved about 2000 
grs.; this would be called a hot saturated solution. 

As a general rule, solids are dissolved more 
quickly and in larger quantity by hot water 
than by cold. 

One of the commonest methods of crystal- 
lising a solid substance, consists in dissolving 
it in hot water, and allowing the solution to 
cool slowly. The more slowly it cools, the 
larger and more symmetrical are the crystals. 

A hot saturated solution is not generally the 
best for crystallising, because it deposits the 
dissolved body too rapidly. Thus the hot 
solution of saltpetre prepared as above would 
solidify to a mass of minute crystals on cooling ; 
but if 1000 grs. of saltpetre be dissolved in 4 
measured ounces of boiling water, it will form crystals 
long when slowly cooled (in a covered vessel), 




Fig. 43. 



of 2 or 3 inches 
If the solution be stirred 
while cooling, the crystals will be very minute, having the appearance of 
a white powder. 

Some solids, however, refuse to crystallise, even from a hot saturated 
solution, if it be kept absolutely undisturbed. 

Sulphate of soda affords a good example of this. If the crystallised sulphate be 
added to boiling water in a flask, as long as it is dissolved, the water will take into 
solution more than twice its weight of the salt, yielding a solution which boils at 
220° F. If this solution be allowed to cool in the open flask, an abundant crystallisa- 
tion will take place, for cold water will dissolve only about one-third of its weight of 
crystallised sulphate. But if the flask (which should be globular) be tightly corked 
whilst the solution is boiling, it may be kept for several days without crystallising, 
although moved about from one place to another. In this condition the solutionjs 
said to be super-saturated. On withdrawing the cork, the air entering the partly 
vacuous space above the liquid will be seen to disturb the surface slightly, and from 
that point beautiful prismatic crystals will shoot through the liquid until the whole 
has become a nearly solid mass. A considerable elevation of temperature is observed, 
consequent upon the passage from the liquid to the solid form. If the solution of 
sulphate of soda be somewhat weaker, containing exactly two-thirds of its weight of 
the crystals, it may be cooled without crystallising, even in vessels covered with 
glass plates, but a touch with a glass rod will start the crystallisation immediately.* 

A super-saturated solution may always be made to crystallise by dropping in a 
minute crystal of the salt present in the liquid. 

Minute solid particles {nuclei) derived from the air appear to be instrumental in 
causing the crystallisation of super-saturated solutions. If the solution of sulphate 
of soda containing two-thirds of its weight of the crystallised salt be allowed to cool 
in a flask closed by a cork furnished with two tubes closed with plugs of cotton wool, 
it will be found that on withdrawing the plugs and blowing air through one of the 
tubes dipping into the solution, crystallisation does not take place, apparently be- 
cause the air has been deprived .of the particles capable of causing it ; for if air 
be blown through the same solution with the bellows, it solidifies almost instan- 
taneously. 

A most beautiful illustration of the power of unfiltered air to start crystallisation 
is afforded by a solution of alum which has been saturated at 194° F.f and. allowed to 

* It is very remarkable that, if the glass rod has been recently heated, it will not cause 
the crystallisation even after it has been cool for some time. 

f J. M. Thomson recommends a solution of alum in half its weight of water for this 
experiment. 



42 WATER OF CRYSTALLISATION. 

cool in a flask, the mouth of which is closed by a plug of cotton wool. In this state 
it may be kept for weeks without ciyst alii sing, but on withdrawing the plug, crystal- 
lisation will be seen to commence at a few points on the surface immediately under 
the opening of the neck, and will spread slowly from these, octahedral crystals of 
alum of half an inch or more in diameter being built up in a few seconds, the tempera- 
ture, at the same time, rising very considerably. 

In the laboratory, stirring is always resorted to in order to induce crystallisation, 
if it does not take place spontaneously. Thus it is usual to test for potash in a 
solution by adding tartaric acid, which should cause the formation of minute crystals 
of bitartrate of potash (cream of tartar), but the test seldom succeeds unless the solu- 
tions are briskly stirred together with a glass rod. An amusing illustration of this 
is afforded by pouring a solution of tartaric acid into a solution of saltpetre, and 
allowing the clear mixture to run over a large plate of glass. Letters traced on the 
glass with the finger will now be rendered visible by the deposition of the crystals of 
bitartrate of potash upon the glass. 

39. The crystals of sodium sulphate produced in the above experiments 
contain, in a state of combination with the salt, more than half their 
weight of water. Their composition is — 

Anhydrous sodium sulphate (Na 2 S0 4 ) 142 parts, or one molecule, 
Water ...... 180 ,, or ten molecules, 

as expressed by the formula ^Na 2 SO 4 .10H 2 O. If some of the crystals 
be pressed between blotting-paper to remove adhering water, and left 
exposed to the air, they will gradually effloresce, or become covered with a 
white opaque powder. This powder is the anhydrous sodium sulphate 
into which the entire crystals would ultimately become converted by 
exposure to air. Since most crystals containing water have their crystalline 
form destroyed or modified by the loss of the water, it is commonly 
spoken of as water of crystallisation. 

Coloured salts, containing water of crystallisation, generally change 
colour when the water is removed. The sulphate of copper (blue stone) 
affords an excellent example of this. The beautiful blue prismatic crystals 
of this salt contain — 

Anhydrous sulphate of copper (CuS0 4 ) 159*5 parts, or one molecule, 
Water . . . . 90 "0 ,, or five molecules, 

as expressed by the formula CuS0 4 .5H 9 0. 

When these are exposed to the air at the ordinary temperature they 
remain unchanged ; but if heated to the boiling-point of water they 
become opaque, and may be easily crumbled down to a white powder. 
This powder contains — 

Anhydrous sulphate of copper (CuS0 4 ) 159*5 parts, or one molecule, 
Water . . . . . .18 ,, or one molecule, 



and would therefore be represented by CuS0 4 .H 2 0. The four molecules 
of water, which have been expelled, constituted the water of crystallisation, 
upon which the form and colour of the sulphate of copper depend. If 
the white powder be moistened with water, combination takes place, with 
great evolution of heat, and the blue colour is reproduced. The one 
molecule of water which still remains is not expelled until the salt is 
heated to 390° F. (199° C), proving that it is held to the sulphate of 
copper by a more powerful chemical attraction. On this account it is 
spoken of as ivater of constitution, and in order that the formula of the 
salt may exhibit the difference between the water of constitution and of 
crystallisation, it is usually written CuS0 4 . H 2 0.4Aq.* 

* Aqua, water. 



HYDRATES — NATURAL WATERS. 43 

(Definition. — Water of crystallisation of salts is that which is gene- 
rally expelled at 212° F. (100° C), and is connected with the form and 
colour of the crystals. Water of constitution is not generally expelled at 
212° F., and is in more intimate connexion with the chemical properties of 
the salt.) 

Several of the so-called sympathetic inks employed for writings which 
are invisible until heated, depend upon the change of colour which results 
from the loss of water of crystallisation. Characters written with a weak 
solution of chloride of cobalt and allowed to dry, are very nearly in- 
visible, since the pink colour of so small a quantity of the salt is scarcely 
noticed ; but on warming the paper, the pink hydrated chloride of cobalt 
(CoCl 2 .6Aq.) loses water of crystallisation, and the blue chloride with 1 
Aq. is produced. On exposure to air this again absorbs water, and the 
writing fades away. 

Some salts have so great a tendency to combine with water that they 
become moist or deliquesce when exposed to air. This deliquescence is 
exhibited in a marked degree by chloride of calcium, and its great attrac- 
tion for water is turned to advantage in drying air and other gases by 
passing them through tubes filled with the salt. 

Nearly all salts appear to combine with water at very low temperatures ; 
such compounds, which are decomposed at temperatures above 0° C, have 
been termed cryo-hydrates (Kpvos, frost). 

40. Most bases are capable of combining with water to form hydrates, 
as exemplified in the slaking of lime. Anhydrous lime or quick-lime 
(CaO), when wetted with water, combines with it, evolving much heat, 
and crumbling to a loose bulky powder, which is hydrate of lime or slaked 
lime (CaO.H 2 0). At a red heat the water is expelled, and anhydrous 
lime remains. 

41. According to modern views, based upon the fact that several 
hydrates do not yield water when heated, the hydrate of a metal is defined 
as a compound formed by the replacement of a part of the hydrogen in 
water by a metal ; thus potassium hydrate KHO is formed from water 
H 2 by the replacement of H by K ; calcium hydrate Ca(HO) 2 is formed 
from two molecules of water (H 2 0) 2 by the replacement of H 2 by 
(diatomic) calcium. The imaginary group HO, hydroxyle, would then be 
the radical of the hydrates, which are often termed hydroxides. 

42. Water from Natural Sources. — Pure water is not found in 
nature. Eain is the purest form of natural water, but contains certain 
gases which it collects from the atmosphere during its fall. As soon as 
it reaches the earth it begins to dissolve small portions of the various 
solid materials with which it comes in contact, and thus becomes charged 
with salts and other substances to an extent varying, of course, with the 
nature of the soils and rocks which it has touched, and attaining its 
highest point in sea water, which contains a larger proportion of saline 
matters than water from any other natural source. 

If a quantity of rain, spring, river, or sea water be boiled in a flask 
furnished with a tube also filled with the water, and passing under a gas 
cylinder standing in a trough of the same water (fig. 44), it will be found 
to give off a quantity of gas which was previously held in solution by 
the water, and is now set free because gases are less soluble in hot than in 



44 



WATER OF WELLS, SPRINGS, AND RIVERS. 




Fig. 44. 



cold water. The quantity of this gas will vary according to the source of 
the water, but it will always be found to contain the gases existing in 
atmospheric air, viz,, nitrogen, oxygen, and carbonic acid gas. One gallon 

of rain water will generally 
furnish about 4 cubic inches 
of nitrogen, 2 cubic inches of 
oxygen, and 1 cubic inch 
of carbonic acid gas. It is 
worthy of remark, that the 
nitrogen and oxygen have 
been dissolved by the water, 
not in the proportions in 
which they exist in the 
atmosphere (4N : 10), but in 
the proportions in which they 
ought to be dissolved, if it be 
true that they exist in the air 
in the condition of mere 
mechanical admixture. The 
oxygen thus carried down 
from the air by rain appears to be serviceable in maintaining the respiration 
of aquatic animals, and in conferring upon river waters a self-purifying 
power, by acting upon certain organic matters which would probably 
prove hurtful to animals, and converting them into harmless products of 
oxidation. In the cases of rivers contaminated with the sewage of towns, 
this action of the dissolved oxygen is probably of great importance. The 
carbonic acid dissolved in rain water also probably serves some useful 
purposes in the chemical economy of nature. (See Carbonic Acid.) 

The co -efficient of solubility of a gas expresses the volume of gas absorbed by one 
volume of water. The numbers '02989 and '01478 respectively represent the volumes 
of oxygen and nitrogen absorbed by one volume of water, when exposed to the action 
of either gas, in a pure state, at 59° F. (15° C. ). When a mixture of gases is brought 
into contact with water, the proportions in which the gases are absorbed can be ascer- 
tained by multiplying the co-efficient of solubility of each gas into its proportion by 
volume in the mixture. Thus, when water is exposed to air, containing \ volume of 
oxygen andf volume of nitrogen, the quantities dissolved by 1 volume of water are, — 
Oxygen, A x '02989 =-- '00597 

Nitrogen, f x '01478 = '01182 

or almost exactly 2 volumes of N to 1 volume of O. 

43. The waters of wells, springs, and rivers, and especially those of 
the two first-named sources, differ very much from each other, according 
to the nature of the layers of rock or earth over or through which they 
have passed, and from which they dissolve a great variety of substances, 
some of which are familiar to us in daily life, while others are only met 
with in chemical collections. Under the former head may be enumerated 
Glauber's salt (sodium sulphate), common salt (sodium chloride), Epsom 
salt (magnesium sulphate), gypsum (calcium sulphate), chalk (calcium 
carbonate), common magnesia (magnesium carbonate), carbonic acid, and 
silica. 

Among the substances known only to the chemist may be mentioned 
sulphuretted hydrogen, potassium sulphate, potassium chloride, calcium 
chloride ; magnesium chloride, phosphates, bromides and iodides of calcium 



HARD WATERS. 45 

and magnesium (rarely), aluminium sulphate, carbonate of iron (ferrous 
carbonate), and certain vegetable substances.* 

The well waters of certain localities (as, for example, those of large towns) 
also frequently contain salts of nitric and nitrous acids, and of ammonia. 

The waters of springs and rivers do not differ very materially from 
well waters as to the nature of the substances which they contain, though, 
in the case of river waters more particularly, the quantity of these sub- 
stances is materially iufluenced by the conditions of rapid motion and 
exposure to air under which such waters are placed. 

Household experience has established a classification of the waters 
from natural sources into soft and hard waters — a division which depends 
chiefly upon the manner in which they act upon soap. If a piece of 
soap be gently rubbed in soft water (rain water, for example) it speedily 
furnishes a froth or lather, and its cleansing powers can be readily 
brought into action ; but if a hard water (spring water) be substituted for 
rain water, the soap must be rubbed for a much longer time before a 
lather can be produced, or its effect in cleansing rendered evident; a 
number of white curdy flakes also make their appearance in the hard 
water, which were not seen when soft water was used. The explanation 
of this difference is a purely chemical one. 

Soap is formed by the combination of a fatty acid with an alkali ; it is 
manufactured by boiling oil or fat with potash or soda, the former for 
soft, the latter for hard soaps. In the preparation of ordinary hard soap, 
the soda takes from the oil or fat two acids, — stearic and oleic acid, — 
which exist in abundance in most varieties of fat, and unites with them 
to form soap, which in chemical language would be spoken of as a mix- 
ture of stearate and oleate of sodium. 

If soap be rubbed in soft water until a little of it has dissolved, and 
some Epsom salts (magnesium sulphate) be dissolved in water, and 
poured into the soap water, curdy flakes will be produced, as when soap 
is rubbed in hard water, and the soap water will lose its property of froth- 
ing when stirred; the magnesium sulphate has decomposed the soap, form- 
ing sodium sulphate, which remains dissolved in the water, and insoluble 
curdy flakes, which consist of stearate and oleate of magnesium. 

Similar to the effect of the magnesium sulphate is that of hard waters ; 
their hardness is attributable to the presence of the different salts of 
calcium and magnesium, all of which decompose the soap in the manner 
exemplified above ; the peculiar properties of the soap in forming a lather 
and dissolving grease can therefore be manifested only when a sufficient 
quantity has been employed to decompose the whole of the salts of calcium 
and magnesium contained in the quantity of water operated on, and thus a 
considerable amount of soap must be rendered useless when hard water is 
employed. 

On examining the interior of a kettle in which spring, well, or river 
water has been boiled, it will be found to be coated more or less thickly 
with a fur or incrustation, generally of a brown colour, and the harder 
the water the more speedily will this incrustation be deposited. A 
chemical examination shows this deposit to consist chiefly of calcium 
carbonate in the form of minute crystals, which may be discovered by the 

* Although it is certainly known that the acids and bases capable of forming the salts 
here enumerated may be detected in spring and river waters, their exact distribution 
amongst each other is still a matter of uncertainty. 



46 INCRUSTATIONS IN BOILERS. 

microscope ; it usually contains, in addition, some magnesium carbonate, 
calcium sulphate, and small quantities of sesquioxide of iron (rust), and 
vegetable matter, the last two substances imparting its brown colour. In 
order to explain the formation of this deposit, it is necessary to be c come 
acquainted with the particular condition in which the calcium carbonate 
exist in natural waters ; it is hardly dissolved to any perceptible extent 
by pure water, though it may be dissolved in considerable quantity by 
carbonic acid. This statement, which is of great importance in connexion 
with natural waters, may be verified in the following manner : — A little 
slaked lime is well shaken up in a bottle of distilled or rain water, which 
is afterwards set aside for an hour or two ; as soon as that portion of the 
lime which has not been dissolved has subsided, the clear portion is care- 
fully poured into a glass, and a little soda water or solution of carbonic 
acid in water is added to it ; the first addition of the carbonic acid to the 
lime water causes a milkiness, due to the formation of minute particles 
of calcium carbonate ; this being insoluble in the water, separates from 
it, or precipitates, and impairs the transparency of the liquid ; a further 
addition of carbonic acid water renders the liquid again transparent, for 
the carbonic acid dissolves the calcium carbonate which has separated. 

If this clear solution be introduced into a flask, and boiled over the 
spirit-lamp or gas-flame, it will again become turbid, for the free carbonic 
acid will be expelled by the heat, and the calcium carbonate will be 
deposited, not now, however, in so fine a powder as before, but in small, 
hard grains, which have a tendency to fix themselves firmly upon the 
sides of the flask, and, when examined by the miscroscope, are seen to 
consist of small crystals. 

In a similar manner, when natural waters are boiled, the carbonic 
acid gas which they contain is expelled, and the carbonates of calcium 
magnesium and iron are precipitated, since they are insoluble in water 
which does not contain carbonic acid. But, by the ebullition of the water, 
a portion of it has been dissipated in vapour, and if there be much calcium 
sulphate present, the quantity of water left may not be sufficient to retain 
the whole of the salt in solution • and this is the more likely to happen, 
because calcium sulphate requires about 500 parts of water to dissolve it ;* 
a quantity of calcium sulphate, then, is liable to be deposited together with 
the carbonates, and, should the water contain much vegetable matter, this is 
often deposited in an insoluble condition, the whole eventually forming 
together a hard compact mass, composed of successive thin layers, on the 
bottom aud sides of the vessel in which the water has been boiled. The 
" furring " of a kettle is objectionable, chiefly in consequence of its 
retarding the ebullition of the water, since the deposit is a very bad con- 
ductor of heat, and therefore impedes the transmission of heat from the 
fire to the water ; hence the common practice of introducing a round stone 
or marble into the kettle, in order, by its perpetual rolling, to prevent the 
particles of calcium carbonate from forming a compact layer. In steam 
boilers, however, even more serious inconvenience than loss of time some- 
times arises if this deposit be allowed to accumulate, and to form a thick 
layer of badly conducting material on the bottom of the boiler, since the 

* Calcium sulphate has been found nearly insoluble in water having a higher tempera- 
ture than 212° F., as would be the case in boilers worked under pressure, so that it would 
readily be deposited. It is said that waters containing little or no calcium sulphate yield 
a loose and frialle deposit 



CALCAREOUS WATERS. 47 

latter is then liable to become red hot, and should the incrustation happen 
to crack, and allow the water to reach the red hot metal, so violent a dis- 
engagement of steam follows, that boilers have been known to burst under 
the sudden pressure. But even though this calamity be escaped, the 
wear and tear of the boiler is very much increased in consequence of the 
formation of this deposit, since its hardness often renders it necessary to 
detach it with the hammer, much to the injury of the iron boiler-plates, 
which are also subject to increased oxidation and corrosion in consequence 
of the high temperature which the incrustation permits them to attain 
by preventing their contact with the water. Many propositions have 
been brought forward for the prevention of these incrustations ; some sub- 
stances have been used, of which the action appears to be purely mechani- 
cal, in preventing the aggregation of the deposited particles. Clay, saw- 
dust, and other matters have been employed with this view; but the 
action of sal ammoniac, which has also been found efficacious, must be 
explained upon purely chemical principles. When this salt is boiled with 
calcium carbonate, mutual decomposition ensues, resulting in the production 
of calcium chloride and ammonium carbonate, of which salts the former 
is very soluble in water, while the latter passes off in vapour with the 
steam.* 

The deposit formed in boilers fed with sea water consists chiefly of 
calcium sulphate and magnesium hydrate, the latter resulting from the 
decomposition of the magnesium chloride present in sea water, 

The incrustations formed in cisterns and pipes by hard water are also 
produced by the carbonates of calcium and magnesium deposited in conse- 
quence of the escape of the free carbonic acid which held them in solution. 
Many interesting natural phenomena may be explained upon the same 
principle. The so-called petrifying springs, in many cases, owe their re- 
markable properties to the considerable quantity of calcium carbonate dis- 
solved in carbonic acid which they contain ; when any object, a basket, for 
example, is repeatedly exposed to the action of these waters, it becomes 
coated with a compact layer of the carbonate, and thus appears to 
have suffered conversion into limestone. The celebrated waters of the 
Sprudel at Carlsbad, of San-Filippo in Tuscany, and of Saint Allyre 
in Auvergne ; are the best instances of this kind. 

The stalactites and stalagmites,^ which are formed in many caverns 
or natural grottoes (fig. 45), afford beautiful examples of the gradual 
separation of calcium carbonate from water charged with carbonic acid. 
Each drop of water, as it trickles through the roof of the cavern, becomes 
surrounded with a shell of calcium carbonate, the length of which is pro- 
longed by each drop as it falls, till a stalactite is formed, varying in colour 
according to the nature of the substances which are separated from the 
water together with the carbonate (such as the oxides of iron and vege- 
table matter); and as each drop falls from the point of the stalactite upon 
the floor of the cavern, it deposits there another shell, which grows, like 
the upper one, but in the opposite direction, and forms a stalagmite, thus 
adorning the grotto with conical pillars of calcium carbonate, sometimes, 
as in the case of the oriental alabaster, variegated with red and yellow, 
and applicable to ornamental purposes. 

* Solutions of the caustic alkalies, of alkaline carbonates, and arsenites, are also occa- 
sionally employed to prevent the formation of incrustations in boilers. 
*t" From (TTaXa^co, to drop ; cn-a\ayfxa, a drop. 



48 



SOFTENING WATERS. 




Fig. 45. — Stalactite cavern. 



When water which has been boiled for some time is compared with 
unboiled water from the same source, it will be found to have become 

much softer, and this can 
now be easily explained, 
for, a considerable portion 
of the salts of calcium and 
magnesium having separ- 
ated from the water, the 
latter is not capable of 
decomposing so large a 
quantity of soap. The 
amount of hardness which 
is thus destroyed by boil- 
ing is generally spoken of 
as temporary hardness, to 
distinguish it from the 
'permanent hardness due to 
the soluble salts of calcium 
and magnesium which still 
remain in the boiled water. 
It is customary with analy- 
tical chemists, in reporting 
upon the quality of natural waters, to express the hardness by a certain 
number of degrees which indicate the number of grains of chalk or car- 
bonate of calcium which would be dissolved in a gallon of water containing 
carbonic acid, in order to render its hardness equal to that of the water 
examined, that is, to render it capable of decomposing an equal quantity of 
soap. Thus, when a water is spoken of as having 1 6 degrees of hardness, 
it is implied that 16 grs. of calcium carbonate dissolved in a gallon of 
water containing carbonic acid, would render that gallon of water capable of 
decomposing as much soap as a gallon of the water under consideration. 

The utility of a water for household purposes must be estimated, there- 
fore, not merely according to the total number of degrees of hardness 
which it exhibits, but also by the proportion of that hardness which may 
be regarded as temporary, that is, which disappears when the water is 
boiled. Thus, the total hardness of the New River water amounts to 
nearly 15 degrees, that of the Grand Junction Company to 14 degrees, and 
yet these waters are quite applicable to household uses, since their hard- 
ness is reduced by boiling to about 5 degrees. It has been ascertained 
that every degree of hardness in water gives rise to a waste of about 10 grs. 
of soap for every gallon of water employed, and hencB the use of 100 
gallons of Thames or New River water in washing will be attended with 
the loss of about 2 lbs. of soap ; this loss is reduced, however, to about 
one-third when the temporary hardness has been destroyed by boiling. 
The addition of washing soda (sodium carbonate) removes not only the 
temporary, but also the permanent hardness due to the presence of the 
sulphates of calcium and magnesium in the water, for both these salts are 
decomposed by the sodium carbonate which separates the calcium and 
magnesium as insoluble carbonates, while sodium sulphate remains dis- 
solved in the water.* The household practice of boiling the water, and 



* CaS0 4 
Calcium sulphate. 



Na 3 C0 3 = Na 2 S0 4 4- CaCO s 
Sodium carbonate. Sodium sulphate. Calcium carbonate. 



ORGANIC MATTER IN WATER. 49 

adding a little washing soda, is therefore very efficacious in removing 
the hardness. Clark's process for softening waters depends upon the 
neutralisation of the free carbonic acid contained in the water by the 
addition of a certain quantity of lime ; the calcium carbonate so produced 
separates together with the carbonates of calcium and magnesium, which 
were previously retained in solution by the free carbonic acid ; this 
process, therefore, affects chiefly the temporary hardness ; moreover, the 
earthy carbonates which are separated appear to remove from the water 
a portion of the organic matter which it contains, and thus effect a very 
important purification. The water under treatment is mixed, in large tanks, 
with a due proportion of lime previously diffused through water (the 
quantity necessary having been determined by preliminary experiment), 
and the mixture allowed to settle until perfectly clear, when it is drawn 
off into reservoirs.* 

Waters which are turbid from the presence of clay in a state of sus- 
pension, are sometimes purified by the addition of a small quantity of 
alum or sulphate of alumina, when the alumina is precipitated by the 
calcium carbonate, and carries down with it mechanically the suspended 
clay, leaving the water clear. 

The organic matter contained in waters may be vegetable matter dis- 
solved from the earth with which it has come in contact, or resulting 
from the decomposition of plants, or it may be animal matter derived 
either from the animalcules and fish naturally existing in it, or from the 
sewage of towns, and, in the case of well waters, from surface drainage. 
It is a pretty generally received opinion that such of these organic matters 
as are very susceptible of chemical change have an injurious effect upon 
the system of persons drinking the water, and it is now usual, in examin- 
ing water as to its fitness for consumption, to ascertain how much of the 
organic matter is in a changeable condition, by determining with the aid 
of a solution of potassium permanganate the amount of oxygen necessary 
to effect its conversion into more stable forms. 

It is believed upon good medical authority, that cholera, diarrhoea, and 
typhoid fever are propagated by certain spores or germs, which are present 
in the evacuations of persons suffering from those maladies, and are 
conveyed into water which is allowed to become contaminated by 
sewage. 

On this account, much attention is paid, in the analysis of water 
intended for drinking, to the detection of organic matters containing 
nitrogen (so-called albuminoid matters) which would be conveyed into the 
water in such evacuations. The analytical operations required for this 
purpose require great care and skill, and the conclusions to be drawn from 
their results are by no means finally agreed upon among scientific 
chemists. 

There are, however, certain simple tests, which may often determine whether it is 
worth while to undertake a more elaborate examination of the water. 
• 1. Pour half a pint of the water into a wide-mouthed bottle or decanter, close it 
with the stopper or with the palm of the hand, and shake it violently up and down. 
If an offensive odour is then perceived, the water is probably contaminated by 
sewage-gas, and possibly with other constituents from the same source. 

2. Add to a little of the water a drop or two of dilute sulphuric acid, and enough 
potassium permanganate (Condy's red fluid or ozonised water) to tinge it of a faint 

* Thames and New River water are softened, in this way, to 3*5, or to a lower point than 
bv an hour's boiling. 



50 MINEEAL WATERS. 

rose colour ; cover the vessel with a glass plate or a saucer. If the pink tinge be 
still visible after the lapse of a quarter of an hour, the water is probably whole- 
some. 

3. Pour a little solution of silver nitrate {lunar caustic) into a carefully cleaned 
glass, and see that it remains transparent ; then pour in some of the water ; should 
a strong milkiness appear, which is not cleared up on adding a little diluted nitric 
acid, the water probably contains much sodium chloride, which is always found in 
sewage-water, but seldom in wholesome waters in any large quantity, unless near the 
sea-coast. 

To render an impure water fit to drink, a chemist would naturally recommend 
distillation, but in many cases this is impracticable, and the consumer may protect 
himself to a great extent by boiling the water, or by filtering it through char- 
coal or spongy iron, or by applying Clark's process (p. 49), or treating it with alum 
(p. 49). 

44. One of the most important points to be taken into account in 
estimating the qualities of a water is its action upon lead, since this metal 
is unfortunately so generally employed for the storage and transmission of 
water, and cases frequently occur in which the health has been seriously 
injured by repeated small doses of compounds of lead taken in water 
which has been kept in a leaden cistern. If a piece of bright freshly 
scraped lead be exposed to the air, it speedily becomes tarnished from the 
formation of a thin film of the oxide of lead, produced by the action of 
the atmospheric oxygen ; this oxide of lead is soluble in water to some 
extent, and hence, when lead is kept in contact with water, the oxygen 
which is dissolved in it acts upon the metal, and the oxide so produced 
is dissolved by the water ; but fortunately, different waters act with very 
different degrees of rapidity upon the metal, according to the nature of 
the substances which they contain. 

The film of oxide which forms upon the surface of the lead is insoluble, 
or nearly so, in water containing much sulphate or carbonate of calcium, so 
that hard waters may generally be kept without danger in leaden cisterns, 
but soft waters, and those which contain nitrites or nitrates, should not 
be drunk after contact with lead. Nearly all waters which have been 
stored in leaden cisterns contain a trace of the metal, and since the 
action of this poison, in minute doses, upon the system is so gradual 
that the mischief is often referred to other causes, it is much to be 
desired that lead should be discarded altogether for the construction of 
cisterns. 

To detect lead in a water, fill a glass tumbler with it, place this on white paper, 
add a drop or two of diluted nitric acid, and some hydrosulphuric acid, a dark 
brown tinge will be seen on looking through it from above. 

Mineral waters, as they are popularly called, are simply spring waters 
containing so large a quantity of some ingredient as to have a decided 
medicinal action. They are differently named according to the nature of 
their predominating constituent. Thus, a chalybeate water contains a 
considerable quantity of a salt of iron (usually ferrous carbonate dissolved 
by free carbonic acid) ; an acidulous water is distinguished by a large pro- 
portion of carbonic acid, and is well exemplified in the celebrated Seltzer 
water ; a sulphureous or hepatic water has the nauseous odour due to the 
presence of sulphuretted hydrogen. The Harrogate water is eminently 
sulphureous. Saline waters are such as contain a large quantity of some 
salt ; thus the saline springs of Cheltenham are rich in common salt and 
sodium sulphate. 

The chalybeate waters, which are by no means uncommon, become 



DISTILLATION. 



51 



brown when exposed to the air, and deposit a rusty sediment which con- 
sists of the ferric hydrate, formed by the action of the oxygen of the 
air on the carbonate.* 

45. Sea water contains the same salts as are found in waters from other 
natural sources, but is distinguished by the very large proportion of 
sodium chloride (common salt;. A gallon of sea water contains usually 
about 2500 grains of saline matter, of which 1890 grains consist of 
common salt. The circumstance that clothes wetted with sea water never 
become perfectly dry is to be ascribed chiefly to the magnesium chloride 
present in the water, which is distinguished by its tendency to deliquesce 
or become damp in moist air. There are two elements, bromine and 
iodine, which are found combined with metals in appreciable quantity 
in sea water, though they are of somewhat rare occurrence in other waters 
derived from natural sources. 

46. By distillation pure water may be obtained from most spring and 
river waters. 

(Definition. — Distillation is the conversion of a liquid into a vapour, 
and its recondensation into the liquid form in another vessel. ) 

Fig. 46 represents the ordinary form of still in common use, in which A is a copper 
boiler containing the water to be distilled ; B the head of the still, which lifts out at 
b, and is connected 
by the neck C with 
the worm D, a tin 
pipe coiled round in 
the tub E, and issu- 
ing at F. The steam 
from the boiler, pass- 
ing into the worm, 
is condensed to the 
liquid state, being 
cooled by the water 
in contact with the 
worm ; this water, 
becoming heated, 
passes off through 
the pipe G, being 
replaced by cold 
water, which is 
allowed to enter 
through H.t 

Another form of 
apparatus for dis- 
tillation of water 
and other liquids is 

shown in fig. 47. A is a stoppered retort, the neck of which fits into the tube of a 
Liebig's condenser (B), which consists of a glass tube (C) fitted by means of corks 
into a glass, copper, or tinned iron tube D, into which a stream of cold water is 
passed by the funnel E, the heated water running out through the upper tube F. 
The water furnished by the condensation of the steam passes through the quilled 
receiver G, into the flask H. Heat is gradually applied to the retort by a ring gas- 
burner. 

Many special precautions are requisite in order to obtain absolutely 

* 2FeC0 3 + + 3H 2 = Fe 2 (OH) d + 2C0 2 
Ferrous Water Ferric Carbon 

carbonate. ' hydrate. dioxide. 

f A rosette gas-burner (K) on Bunsen's principle is very convenient for a small still of 
this description. 




^ w www®Ww 



Fig. 46. 



52 



PHYSICAL- PROPERTIES OF WATER. 



pure distilled water for refined experiments, but for ordinary purposes the 
common methods of distillation yield it in a sufficiently pure condition. 




Fig. 47. — Distillation — Liebig's condenser. 

The saline matters present in the water are of course left behind in the 
still or retort. Sea water is now frequently distilled on board ship when 
fresh water is scarce. The vapid and disagreeable taste of distilled water, 
which is due to its having been deprived of the dissolved air during the 
distillation, is remedied by the use of Normandy's apparatus, which pro- 
vides for the restoration of the expelled air. 

47. The physical properties of water are too well known to require 
any detailed description. Its specific gravity in the liquid state is = 1, 
being taken as the standard to which the specific gravities of liquid and 
solid bodies are referred. 

(Definition. — The specific gravity of a liquid or solid body is its 
weight as compared with that of an equal volume of pure water at 60° F., 
15°-5G.) 

Water assumes the solid form, under ordinary circumstances, at 32° F. 
(0° C), and may be obtained in six-sided prismatic crystals. Snow con- 
sists of beautiful stellate groupings of these crystals. Ice has the specific 
gravity 0*9 184. In the act of freezing, water expands very considerably^ 
so that 174 volumes of water at 60° F. become 184 volumes of ice. The 
breakage of vessels, splitting of rocks, &c, by the congelation of water, 
are due to this expansion. Water passes off in vapour at all temperatures, 
the amount of vapour evolved in a given time of course increasing with 
the temperature. The boiling-point of water is 212° F. (100° C.) 

(Definition. — The boiling-point of a liquid is the constant temperature 
indicated by a thermometer, immersed in the vapour of the boiling liquid, 
in the presence of a coil of platinum wire, to faciltate disengagement of 
vapour, and at a pressure of 30 in., 762 mm. Bar.) 

At and above 212° F. at "the ordinary atmospheric pressure (30 in. Ear.), 
water is an invisible vapour of specific gravity 0*622 (air =1). One 
cubic inch of water at 60° F. becomes 1696 cubic inches of vapour at 
212° F. 

Since the specific gravity of a gas or vapour is the weight of one 



PEEOXIDE OF HYDROGEN. 5d 

volume (p. 16), and the molecule of a compound gas occupies two 
volumes, the specific gravity of a compound gas or vapour, referred to 
hydrogen as the standard, is the half of its molecular weight. 

Thus the molecular weight of steam being 18, its specific gravity 
(H=l) would be 9. 

If the specific gravity in relation to air be required, it may be obtained 
by multiplyiug half the molecular weight by 0O692, which represents 
the specific gravity of hydrogen referred to air as the unit. Thus the 
specific gravity of steam (air = 1) is 9 x 0*0692 = "6228. 

48. Peroxide of hydrogen or hydric per 'oxide, H 2 2 . This compound is seldom met 
with in nature, and has no very important useful application in the arts, but it 
possesses very great interest for the student of chemical philosophy, because it helps 
to throw some light upon the molecular constitution of the elements. 

To prepare the peroxide of hydrogen, some baryta (BaO) is heated in a current of 
oxygen, when it becomes converted into the barium dioxide (Ba0. 2 ), If this be 
powdered, suspended in water, and acted upon by a stream of carbonic acid gas, the 
water becomes charged with the hydric peroxide ; Ba0 2 + H 2 + C0. 2 = BaC0 3 + H 2 2 . 
The barium carbonate is allowed to subside, and the clear solution of hydric peroxide 
poured off. 

To prepare pure hydric peroxide, some barium dioxide (Ba0 2 ) is heated to the 
temperature at which it begins to evolve oxygen, and dissolved in as little diluted 
nitric acid as possible. To this solution one of barium hydrate (baryta water) is 
added; the precipitate, Ba0 2 .8H 2 is washed by decantation, and decomposed by 
diluted sulphuric acid, care being taken not to render the liquid acid, Ba0 2 + H 2 S0 4 
= H 2 2 + BaS0 4 . 

The precipitate is allowed to subside, and the clear liquid evaporated in the ex- 
hausted receiver of the air-pump over a dish of oil of vitriol to absorb the water, which 
evaporates much more rapidly than the peroxide. The pure hydric peroxide is a 
syrupy liquid of sp. gr. 1*453, with a very slight chlorous odour. Its most remark- 
able feature is the facility with which it is decomposed into water arid oxygen.* 
Even at 70° F. it begins to evolve bubbles of oxygen. ' At 212° it decomposes with 
violence. The mere contact with certain metals, such as gold, platinum, and silver, 
which have no direct attraction for oxygen, will cause the decomposition of the 
peroxide without any chemical alteration of the metal itself. t Manganese dioxide 
decomposes it without undergoing any apparent change. The most surprising effect 
is that which takes place with silver oxide. If a drop of hydric peroxide be allowed 
to fall upon silver oxide, which is a brown powder, decomposition takes place with 
explosive violence and great evolution of heat, the silver oxide losing its oxygen, and 
becoming grey metallic silver. + The oxides of gold and platinum are acted upon in 
a similar manner. 

These very extraordinary changes, which were formerly described as catalytic actions, 
are now generally accounted for by the hypothesis that the oxygen in the oxide of 
silver, &c, exists in a condition different from that of the second atom of oxygen in 
the hydric peroxide, and that these two conditions of oxygen have a chemical attrac- 
tion for each other, similar to that which exists between different elements. If the 
oxygen in the silver oxide be represented as electro-negative oxygen (see 5), as its 
relation to the metal would lead us to expect, and the second atom of oxygen in the 
hydric peroxide be represented as electro -positive oxygen, the mutual decomposition 
of the two compounds might be represented by the equation, 

+ _ + 

Ag 2 + H 2 00 = Ag 2 + H 2 + O. 
The elementary substances, with few exceptions, have molecules composed of two 
atoms, which may be due to the circumstance that each atom is associated with an 

* The presence of a little free acid renders it rather more stable, whilst free alkali has 
the opposite effect. A solution of hydric peroxide, containing a little hydrochloric acid, is 
now sold for medicinal and photographic uses. 

*t* Such inexplicable changes as this are sometimes included under the general denomina- 
tion of catalysis, or decomposition by contact. 

% If ammonia be very carefully added to silver nitrate until the precipitate formed at 
first is only just re-dissolved, the solution will give a lustrous deposit of metallic silver on 
addition of a little hydric peroxide, and gently heating. 



54 OZONE. 

equal amount of opposite electricity, and is therefore the complement of the 
other. 

If hydric peroxide, even in diluted solution, be added to potassium perman- 
ganate acidified with sulphuric acid, the red colour is entirely destroyed, and bubbles 
of, oxygen are evolved, causing effervescence; K 2 Mn 2 8 + 3H 2 S0 4 -b5H 2 2 = K 2 S0 4 
+ 2MnS0 4 + 8H 2 + 50 2 . Here 5 from the hydric peroxide have united with 5 
from the permanganate. 

These experiments support the conclusion arrived at by the reasoning at page 2, that 
the molecule or ultimate physical particle of oxygen is really composed of 2 atoms. 

A very striking reaction of hydric peroxide is that with chromic acid. If a solution 
of H. 2 2 be added to a weak solution of potassium bichromate acidified with sul- 
phuric acid, the beautiful blue colour of perchromic acid appears : K 2 Cr 2 7 + H 2 S0 4 + 
2H 2 2 = K 2 S0 4 + 3H. 2 + H 2 Cr 2 8 . After a few minutes, the blue colour changes 
to a very pale green, the perchromic acid being decomposed by the sulphuric acid, 
yielding the green chromium sulphate, and free oxygen which adheres in bubbles to 
the side of the vessel , H 2 Cr 2 8 + 3 H 2 S0 4 = Cr. 2 (S0 4 ) 3 + 4H 2 + 4 . If the blue solution 
be shaken with a little ether which dissolves the perchromic acid and rises with it 
to the surface where it forms a blue layer, the colour is much more lasting, and very 
minute quantities of hydric peroxide may thus be detected. 

49. Ozone. — This is the name given to a modified form of oxygen, of the true 
nature of which there is still some doubt, as it has never been obtained unmixed with 
ordinary oxygen, but it appears to be formed by the union of 3 atoms of oxygen 
(occupying 3 volumes), to produce a molecule of ozone (occupying 2 volumes). 
Just as hydric peroxide (H 2 2 ), may be regarded as formed by the combination of 
a molecule of water (H 2 0) with an atom of oxygen, so ozone may be viewed as a 
combination of a molecule of oxygen (0 2 ) with an atom of oxygen. It would then be 
half as heavy again as ordinary oxygen, and experiment has shown that its rate of 
diffusion is in accordance with this view. 

It derives its name from its peculiar odour {'6£eiv, t° smell), which is often perceived 
in the air of the sea or of the open country, and in linen which has been dried in 
country air. According to Hartley, 1 volume of ozone in 1\ million vols, of air 
may be perceived by the smell. Oxygen appears to be capable of assuming this 
ozonised condition under various circumstances, the principal of which are, the 
passage of silent electric discharges,* and the contact with substances (such as 
phosphorus) undergoing slow oxidation in the presence of water. A minute 
proportion of the oxygen obtained in the decomposition of water by the galvanic 
current also exists in the ozonised condition, as may be perceived by its odour. 

The use of Siemens' induction tube (fig. 48) affords the readiest method of demon- 
strating the characteristic 
properties of ozone. This 
apparatus consists of a 
tube (A) coated internally 
with tin-foil (or silvered 
on the inside), and sur- 
rounded with another tube 
(B), which is coated with 
tin -foil on the outside._ 
"When the inner and outer 
coatings are placed in con- 
nexion with the wires of 
an induction coil by means 
Fig. 48.— Tube for ozonising air by induction. of the screws (CD), and a 

stream of air or oxygen 
(dried by passing through oil of vitriol) is passed through (E) between the two tubes, 
a strong odour is perceived at the orifice (F). 

Several forms of apparatus upon this principle have been constructed for obtaining 
large volumes of ozonised air. Plates of glass coated with tin-foil will ozonise the air 
between them when the coatings are connected with opposite poles of the induction- 
coil. A wide glass tube or cylinder with a platinum wire, or a piece of platinum-foil 
inside, connected with one pole of the coil, and a platinum wire wound round it 
externally, connected with the other pole of the coil, will ozonise the air passed 
through it, When large quantities of ozone are required, it is found expedient to 

* It is the odour of ozone which is perceived in working an ordinary electrical 
machine. 




PROPERTIES OF OZONE. 55 

employ concentric cylinders filled with water, which serves to keep down the tempera- 
ture, and may be employed, instead of a metallic coating, to receive the charge of 
electricity. 

The ordinary chemical test for ozone is a damp mixture of starch with potassium 
iodide. 100 grains of starch are well mixed in a mortar with a measured ounce of 
cold water, and the mixture is slowly poured into 5 ounces of boiling water in a 
porcelain dish, with occasional stirring. The thin starch-paste thus obtained is 
allowed to cool, and a few drops of solution of pure potassium iodide are added, the 
mixture being well stirred with a glass rod. If this mixture be brushed over strips 
of white cartridge paper, these will remain unchanged in ordinary air ; but when they 
.are exposed to ozonised air (such as that which has passed through the induction 
tube), they will immediately assume a blue colour. The ozonised oxygen being more 
active, or endowed with more powerful chemical attraction than ordinary oxygen, 
abstracts the potassium from the potassium iodide (KI), and sets free the iodine, which 
has the specific property of imparting a blue colour to starch. The intensity of the 
blue tint is proportionate to the quantity of iodine liberated, and therefore to that 
of the ozonised oxygen present, and hence, by reference to a standard scale of colours 
previously agreed upon, the ozone may be expressed in degrees. The result, however, 
is affected by so many trifling circumstances, that it is doubtful whether such deter- 
minations of the quantity of ozone are to be considered trustworthy. More satis- 
factory tests are afforded by papers impregnated with manganese sulphate or lead 
acetate, which become brown from the formation of the binoxides of those metals 
under the influence of ozone. 

If the ozonised air issuing from F be passed into a solution of indigo {sulphindigotic 
acid largely diluted) th3 blue colour will soon disappear, since the ozone oxidises the 
indigo, and gives rise to products which, in a diluted state, are nearly colourless. 
Ordinary oxygen is incapable of bleaching indigo in this manner. If the ozone is 
passed through a tube of vulcanised caoutchouc, this will soon be perforated by the 
corrosive effect of the ozone, whilst ordinary oxygen would be without effect upon it. 
If ozonised air be passed into a flask with a little mercury at the bottom, the surface 
of the mercury will soon become tarnished by the formation of oxide, and when the 
mercury is shaken round the flask it will adhere to the sides, which is not the case 
with pure mercury. 

If the ozone from F be made to pass slowly through a glass tube heated in the 
centre by a spirit-lamp, it will be found to lose its power of affecting the iodised 
starch-paper, the ozone having been reconverted into ordinary oxygen under the influ- 
ence of heat; 2(00 2 ) = 3(0 2 ). A temperature of 300° F. is sufficient to effect this change. 
It has been observed that a given volume of oxygen diminishes when a portion of it 
is converted into ozone by the silent electric discharge, and that it regains its original 
.volume when the ozone is reconverted by heat, proving that the ozonised form of 
oxygen is denser, or occupies less space than the ordinary form. 

When a given quantity of oxygen is electrised, or subjected to the action of surfaces 
charged with opposite electricities, only one-fifth, at most, is converted into ozone ; 
but if the ozone be now removed by some substance which absorbs it, a fresh quantity 
of the oxygen may be ozonised. 

The researches of Brodie have shown that either one, two, or three atoms of oxygen in 
ozone may be absorbed, according to the nature of the oxidisable substance employed. 
Thus, where a neutral solution of potassium iodide is acted on by ozone, 

00 2 (2 volumes) + 2KI + H 2 = 2KHO + I 2 + 2 (2 volumes), 

the atom of oxygen being removed without diminution in the volume of the gas. But 
if the solution of potassium iodide be acidified (and thus converted, virtually, into a 
solution of hydriodic acid), 

00 2 (2 volumes) + 4HI = 2H 2 + I 4 + (1 volume), 
the volume being here reduced by one-half. When chloride of tin (stannous chloride) 
mixed with hydrochloric acid is brought in contact with ozone, the latter is entirely 
absorbed, converting the stannous chloride into stannic chloride, 

00 2 + 3SnCl 2 + 6HC1 = 3SnCl 4 + 3H 2 . 

Oil of turpentine and some other substances also absorb the ozone entirely. 

By placing a freshly-scraped stick of phosphorus (scraped under water to avoid 
inflammation) at the bottom of a quart bottle, with enough water to cover half of it, 
and loosely covering the bottle with a glass plate, enough ozone may be accumulated 
in a few minutes to be readily recognised by the odour and the iodised starch. 



56 



OZONE. 



The water at the bottom of the bottle is found to contain, besides the phosphorous 
and phosphoric acids, formed by the slow oxidation of the phosphorus, some .hydric 
peroxide, whence it has been supposed that the formation of ozone is due to the 
decomposition of a molecule of oxygen into electro-negative oxygen, which combines 
with another molecule of oxygen to form ozone, and electro-positive oxygen which 
combines with a molecule of water to form hydric peroxide. Thus, 
-+ + • - 



0, 



00 + H 9 



+ 0,0 




Fig. 49. 



This view is supported by the circumstance, that hydric peroxide appears to be 
produced in every case where ozone is formed in the presence of water. 

When ozonised oxygen is shaken with hydric peroxide, the above equation is 
reversed, water and ordinary oxygen resulting. 

If a few drops of ether be poured into a quart beaker (fig. 49), taking care to avoid 
the vicinity of a flame, and pieces of iodised starch-paper and blue litmus paper be 

suspended upon a glass rod laid across the mouth 
of the beaker, they will be found unaffected by the 
mixture of ether vapour and air ; but if a hot glass 
rod be plunged into the beaker, the heated ether 
vapour will undergo oxidation, producing pungent 
acid vapours, which redden the blue litmus, whilst 
the formation of ozone will be indicated by the 
blue iodised starch.* 

Ether and essential oils, such as turpentine, 
slowly absorb oxygen from the air, thus acquiring 
the property of bleaching indigo and of blueing the 
mixture of potassium iodide and starch ; hence 
they were formerly believed to contain ozone, but 
they do not answer to all the tests for that sub- 
stance. Thus, ozone imparts a blue colour to the 
resin of guaiacum, but the old turpentine or 
ether will not do so.t If a little hydric peroxide 
be dissolved in ether, it exhibits the same property 
as the ether which has absorbed oxygen from the air, and it is, therefore, sometimes 
called " ozonic ether." The solution of hydric peroxide in ether (obtained by shaking 
the aqueous solution of the peroxide with ether) is employed by Dr. Day for the 
recognition of blood stains. Contact with blood decomposes hydric peroxide, and the 
oxygen which is liberated is capable of blueing guaiacum resin. Accordingly, if a 
blood-stain be moistened with tincture of guaiacum (a solution of the resin in spirit 
of wine), and afterwards with the ethereal solution of hydric peroxide (ozonic ether), 
it acquires an intense blue colour, which may be detected, even on a coloured fabric, 
by pressing a piece of white blotting-paper upon it. 

Ozone has attracted much notice, because a minute proportion of the oxygen in the 
atmosphere appears sometimes to be present in this form, and its active properties 
have naturally led to the belief that it must exercise some influence upon the sanitary 
condition of the air. This idea is encouraged by the circumstance that no indications 
of ozone can be perceived in crowded cities, where there are so many oxidisable 
substances to consume the active oxygen, whilst the air in the open country and at 
the sea-side does give evidence of its presence. Some chemists assert that their 
experiments have demonstrated the very important fact that a portion of the oxygen 
developed by growing plants is in the ozonised form, but the evidence on the 
subject is conflicting. Houzeau fixes the maximum proportion of ozone at y o^ooo th 
of the volume of air. The proportion is highest in May and June, lowest in 
December and January. 

Ozonised oxygen exhibits a sky-blue colour when viewed along a column of one 
metre in length. The blue colour becomes very deep under a pressure of several 
atmospheres, and indications of the liquefaction of the ozone are observed at - 23° C. 
It has been suggested that the blue colour of the sky is due to our regarding it through 
the ozonised atmosphere.* 

* The oxygen obtained by the action of warm sulphuric acid on barium dioxide or on 
crystallised potassium permangnate, resembles ozone in its odour and action on the iodised 
starch paper. 

f Kingzett has shown that the action of air on oil of turpentine produces an organic 
substance which yields hydric peroxide when acted on by water. (See Turpentine.) 

+ "On the Absorption of Solar Rays by Atmospheric Ozone," Hartley, J mm. Chem. Soc, 
March 1881. 



ATMOSPHERIC AIR. 



57 



In want of stability, ozone resembles hydric peroxide ; contact with manganese 
dioxide converts it into ordinary ox} 7 gen. Even shaking with powdered glass will 
de-ozonise the ozonised oxygen. 



ATMOSPHERIC AIR 

50. Atmospheric air consists chiefly of a mixture of nitrogen with one- 
fifth of its volume of oxygen, and very small proportions of carbonic 
acid gas and ammonia. Vapour of water is of course always present in the 
atmosphere in varying proportions. Since the atmosphere is the recep- 
tacle for all gaseous emanations, other substances may be discovered in 
it by very minute analysis, but in proportions too small to have any per- 
ceptible influence upon its properties. Thus marsh-gas or light carburetted 
hydrogen, sulphuretted hydrogen, and sulphurous acid gas, can often be 
traced in it, the two last especially in or near towns. 

Although the proportion of oxygen in the air at a given sp>ot may be 
much diminished, and that of carbonic acid gas increased, by processes of 
oxidation (such as respiration and combustion) taking place there, the 
operation of wind and of diffusion so rapidly mixes the altered air with 
the immensely greater general mass of the atmosphere, that the variations 
in the composition of air in different places are very slight. Thus it has 
been found that the proportion of oxygen in the air in the centre of 
Manchester was, at most, only 0*2 per cent, below the average. 

The proportions in which the oxygen and nitrogen are generally pre- 
sent in atmospheric air, freed from water and carbonic acid gas, are — 
nitrogen, 79*19 per cent, by volume, or 76" 99 per cent, by weight ; oxygen, 
20*81 per cent, by volume, 23*01 per cent, by weight. 

The proportion of aqueous vapour may be stated, on the average, as 1 *4 
per cent, by volume, or 0*87 per cent, by weight of the air. The carbonic 
acid gas may be generally estimated at 0*04 per cent, by volume, or 0*06 
per cent, by weight of the air.* The total weight of atmospheric air 
surrounding the globe exceeds 300,000 million tons. 

The relative proportions of oxygen and nitrogen in air may be exhibited by sus- 
pending a stick of phosphorus upon a wire stand (A, fig. 50) in a measured volume of 
air confined over water. The cylinder (B) should 
have been previously divided into five equal spaces 
by measuring water into it, and marking each space 
by a thin line of Brunswick black. After a few 
hours, the phosphorus will have combined with the 
whole of the oxygen to form phosphorous and phos- 
phoric acids, Avhich are absorbed by the water, 
leaving four of the spaces occupied by nitrogen. 

The same result may be arrived at in a much 
shorter time by burning the phosphorus in the con- 
fined portion of air. 

A fragment of phosphorus, dried by careful pres- 
sure between blotting-paper, is placed upon a con- 
venient stand (A, fig. 51) and covered with a tall 
jar, having an opening at the top for the insertion 
of a well-fitting stopper (which should be greased 
with a little lard), and divided into seven parts of 
equal capacity. The jar should be placed over the stand in such a manner that the 
water may occupy the two lowest spaces into which the jar is divided. The stopper 
of the jar is furnished with a hook, to which a piece of brass chain (B) is attached, 
long enough to touch the phosphorus when the stopper is inserted. The end of this 




Fig. 50. 



Reiset finds somewhat less than *03 per cent, by volume. 



58 



ANALYSIS OF AIR. 



chain is heated in the flame of a lamp, and the stopper tightly fixed in its place. On 
allowing the hot chain to touch the phosphorus, it bursts into vivid combustion, 
filling the jar with thick white fumes, and covering its sides, for a few moments, 

with white flakes of phosphoric anhydride. 
At the commencement of the experiment, the 
water in the jar will be depressed, in conse- 
quence of the expansion of the air, due to the 
heat produced in the burning of the phos- 
phorus, but presently, wdien the combustion 
begins to decline, the water again rises, and 
continues to do so until it has ascended to the 
line (C), so as to occupy the place of one-fifth 
of the air employed in the experiment. The 
phosphorus will then have ceased to burn, the 
white flakes upon the sides of the jar will have 
acquired the appearance of drops of moisture, 
and the fumes will have gradually disappeared, 
until, in the course of half-an-hour, the air 
remaining in the jar will be as clear and trans- 
parent as before, the whole of the phosphoric 
anhydride having been absorbed by the water. 
The jar should now be sunk in water, so that the latter may attain to the same level 
without as within the jar. On removing the stopper, it will be found that the 
nitrogen in the jar will no longer support the combustion of a taper. 

In the rigidly accurate determination of the relative proportions of oxygen and 
nitrogen in the air, it is of course necessary to guard against any error arising from 
the presence of the water, carbonic acid gas, and ammonia. With this view, 




Fig. 51. 




-Exact analysis of air. 

Dnmas and Boussingault, to whom we are chiefly indebted for our exact knowledge of 
the composition of the air, caused it to pass through a series of tubes (A, fig. 52) con- 
taining potash, in order to remove the carbonic acid 
gas, then through a second series (B) containing sul- 
phuric acid, to absorb the ammonia and water; the 
purified air then passed through a glass tube (C) filled 
with bright copper heated to redness in a charcoal 
furnace, which removed the whole of the ox3'gen, and 
the nitrogen passed into the large globe (N). 

Both the tube (containing the copper) and the globe 
were carefully exhausted of air and accurately weighed 
before the experiment ; on connecting the globe and 
the tube with the purifying apparatus, and slowly 
opening the stop-cocks, the pressure of the external air 
caused it to flow through the series of tubes into the 
globe destined to receive the nitrogen. When a con- 
siderable quantity of air had passed in, the stop-cocks 
were again closed, and after cooling, the weight of the 
globe was acccurately determined. The difference 
between this weight and that of the empty globe, before 
the experiment, gave the weight of the nitrogen which 
had entered the globe ; but this did not represent the 
whole of the nitrogen contained in the analysed air, for 
the tube containing the copper had, of course, remained 
full of nitrogen at the close of the experiment. This 
tube, having been weighed, was attached to the air- 
pump, the nitrogen exhausted from it, and the tube again weighed ; the difference 
between the two weighings furnished the weight of the nitrogen remaining in the 




Fig. 53. 



ANALYSIS OF AIR. 59 

tube, and was added to the weight of that received in the globe. The oxygen was 
represented by the increase of the weight of the exhausted tube containing the copper, 
which was partially converted into oxide of copper, by combining with the oxygen of 
the air passed through it. 

The calculation of the result of the analysis is here exemplified : — 

Weight of Grains. 

Globe (N) with nitrogen (at the conclusion), . . . 3076 

Exhausted globe (at the commencement), . . . 3000 

Nitrogen received into the globe, . . . 76 

Tube (C) with residual nitrogen (at the conclusion), . . 2574 

Exhausted tube (at the conclusion), .... . 2573 

Nitrogen remaining in the tube, ... 1 

Add nitrogen received into the globe, . . 76 

Total nitrogen in the air analysed, . . 77 

Exhausted tube (C) with oxidised copper (at the conclusion), . 2573 

,, ,, metallic copper (at the commencement), 2560 

Oxygen in the air analsyed, . . . 23 

The ratio of the nitrogen to the oxygen, therefore, is that of 23 O: 77 N, or 
10:3 "347 N. 100 parts by weight of the air purified from water, carbonic acid gas, 
and ammonia, contain 77 parts of nitrogen and 23 parts of oxygen. 

51. The nitrogen remaining after the removal of the oxygen from air in 
the above experiments was so called on account of its presence in nitre 
(saltpetre KN0 3 ). In physical properties it resembles oxygen, but is 
somewhat lighter than that gas, its specific gravity being - 9713. 

This difference in the specific gravities of the two gases is well exhibited by 
the arrangement shown in fig. 53. A jar of oxygen (O) is closed with a glass 
plate, and placed upon the table. A jar of nitrogen (N), also closed with a glass 
plate, is placed over it, so that the two gases may come in contact when the glass 
plates are removed. The nitrogen will float for some seconds above the oxygen, and 
if a lighted taper be quickly introduced through the neck of the upper jar, it will be 
extinguished in passing through the nitrogen, and will be rekindled brilliantly when 
it reaches the oxygen in the lower jar. 

It might at first sight appear surprising that oxygen and nitrogen, 
though of different specific gravities, should exist in uniform proportions 
in all parts of the atmosphere, unless in a state of chemical combination ; 
but an acquaintance with the property of diffusion (see 13) possessed by 
gases, teaches us that gases ivill mix with each other in opposition to 
gravitation, and when mixed will always remain so. 

It was shown by Graham that a partial separation of the nitrogen and oxygen in air 
may be effected, on the same principle as that of hydrogen and oxygen at page 20, 
by taking advantage of the difference in their rates of diffusion. He devised, 
however, a more convenient process, founded upon the dialytic passage of the gases 
through caoutchouc, which he ascribed to the absorption of the gas by the solid 
material upon one side, and its escape on the other. 

A bag {a, fig. 54) is made of a fabric composed of a layer of caoutchouc between two 
layers of silk, such as that employed for waterproof garments ; a piece of carpet 
is placed inside the bag to keep the sides apart, and the edges of the bag are made 
perfectly air-tight with solution of caoutchouc. To maintain a vacuum within the bag, 
it is supported by a rod v, and attached to SprengeVs air-pump, in which a stream of 
mercury, allowed to flow from a funnel (/") down a tube (c) six feet long, draws the air 
out of the bag, through a lateral tube (h), until all the air is exhausted, which is 



60 



DIALYSIS OF AIR. 



indicated by the barometer tube b, the lower end of which dips into a cistern of mer- 
cury. When the mercury in this tube stands at almost exactly the same height as 

the standard barometer, the exhaustion is 
complete. If a test-tube (d) filled with mer- 
cury be now inverted over the end of the long 
tube c, which is bent upwards for that purpose, 
the bubbles of air which are drawn through 
the sides of the vacuous bag, and carried down 
the long tube by the little pistons of liquid 
mercury as they fall, will pass up into the 
test-tube ; when the latter is filled with the 
gas, its mouth is closed with the thumb, 
withdrawn from the mercury, and a match 
with a spark at the end inserted, when the 
spark will burst out into flame, showing that 
the specimen of air collected is much richer 
in oxygen than ordinary atmospheric air. 
The overflow tube g delivers the mercmy 
which is to be returned to the funnel/. 

The dialytic passage of oxygen through 
caoutchouc into a vacuum is twice as rapid as 
that of nitrogen, so that the air collected in 
the tube contains twice as much oxygen as the 
external air. 

This dialytic passage of gases through solids 
is quite unconnected with the difmsibility of 
the gases, and appears to depend rather upon 
the chemical nature of the gas and of the 
solid. It is thus connected with the occlusion 
of gases by solids, exemplified in the case of 
palladium and hydrogen at page 40. It is in 
consequence of this dialytic passage that tubes 
of iron or platinum, which are quite imper- 
meable by hydrogen at the ordinary temper- 
ature, will allow it to pass rapidly through 
their walls at high temperatures. 

That air is simply a mechanical mixture of its component gases is amply 
proved by the circumstance that it possesses all the properties which 
would be predicted for a mixture of these gases in such proportions ; 
whilst the essential feature of a chemical compound is, that its properties 
cannot be foreseen from those of its constituents. 

The absence of active chemical properties is a very striking feature of 
nitrogen, and admirably adapts it for its function of diluting the oxygen 
in the atmosphere. 

The chemical relations of air to animals and plants will be more appro- 
priately discussed hereafter. (See Carbonic Acid, Ammonia.) 

In coDsidering the composition of air, much attention has been directed 
of late years to the dust or minute particles of solid matter which, 
although much heavier than air, are suspended in it by the action of 
currents, and may always be detected by a beam from the sun or the 
electric lamp or the lime-light, which would be invisible along its track 
through optically pure air. 

The fine particles of mineral substances present in the dust are the 
probable cause of the crystallisation of super-saturated solutions of salts 
(p. 41) when exposed to air. ' The vegetable particles appear to contain 
minute seeds which germinate when deposited in certain liquid or moist 
solid substances, and give rise to mould, mildew, and fermentation. The 
animal particles are believed to contain the germs by the agency of which 
certain forms of disease are spread. 




Fig. 54. — Sprengel's pump. 
Dialysis of air. 



CARBON. 61 

CAKBOK 

C = 12 parts by weight.* 

52. This element is especially remarkable for its uniform presence in 
organic substances. The ordinary laboratory test by. which the chemist 
decides whether a substance under examination is of organic origin, con- 
sists in heating it with limited access of air, and observing whether any 
blackening from separation of carbon (carbonisation) ensues. 

Few elements are capable of assuming so many different aspects as 
carbon. It is met with transparent and colourless in the diamond, opaque, 
black, and quasi-metallic in graphite or black lead, dull and porous in 
wood charcoal, and under new conditions in anthracite, coke, and gas- 
carbon. 

In nature, free carbon may be said to occur in the forms of diamond, 
graphite, and anthracite (the other varieties of coal containing considerable 
proportions of other elements). 

Apart from its great beauty and rarity, the diamond possesses a special 
interest in chemical eyes, from its having perplexed philosophers up to 
the middle of the last century, notwithstanding the simplicity of the ex- 
periments required to demonstrate its true nature. The first idea of it 
appears to have been obtained by Newton, when he perceived its great 
power of refracting light, and thence inferred that, like other bodies 
possessing that property in a high degree, it would prove to be com- 
bustible (" an unctuous substance coagulated "). When the prediction 
was verified, the burning of diamonds was exhibited as a marvellous 
experiment, but no accurate observations appear to have been made till 
1772, when Lavoisier ascertained, by burning diamonds suspended in the 
focus of a burning glass in a confined portion of oxygen, that they were 
entirely converted into carbonic acid gas. In more recent times this 
experiment has been repeated with the utmost precaution, and the 
diamond has been clearly demonstrated to consist of carbon in a crystal- 
lised state. 

A still more important result of this experiment was the exact determination of 
the composition of carbon dioxide, without which it would not be possible to ascertain 
exactly the proportion of carbon in any of its numerous compounds, since it is always 
weighed in that form. 

The most accurate experiments upon the synthesis of carbon dioxide have been 
conducted with the arrangement represented in fig 55. 

Within the porcelain tube A,. which is heated to redness in a charcoal fire, was 
placed a little platinum tray, accurately weighed, and containing a weighed quantity 
of fragments of diamond. One end of the tube was connected with a gas-holder B, 
containing oxygen, which was thoroughly purified by passing through the tube (J, 
containing potash (to absorb any carbonic acid gas and chlorine which it might 
contain), and dried by passing over pumice soaked with concentrated sulphuric acid 
in D and E. To the other end of the porcelain tube A, there was attached a glass 
tube F, also heated in a furnace, and containing oxide of copper to convert into 
carbonic acid gas any carbonic oxide which might have been formed in the combus- 
tion of the diamond. The carbonic acid gas was then passed over pumice soaked 
with sulphuric acid in G, to remove any traces of moisture, and afterwards into a 
weighed bulb-apparatus H, containing solution of potash, and two weighed tubes 
I, K, containing, respectively, solid potash and sulphuric acid on pumice, to guard 
against the escape of aqueous vapour taken up by the excess of oxygen in its passage 
through the bulbs H. The increase of weight in H, I, K, represented the carbonic 

* The volume occupied by carbon in the form of vapour is not known, its vapour never 
having been obtained in a measurable form. 



62 



SYNTHESIS OF CARBON DIOXIDE. 



acid gas formed in the combustion of an amount of diamond indicated by the loss of 
weight suffered by the platinum tray, and the difference between the diamond con- 
sumed and the carbonic acid gas formed would express the amount of oxygen which 




?V 




Fig. 56. 



Fig. 55. — Exact synthesis of carbonic acid gas. 

had combined with the carbon. A large number of experiments conducted in this 
manner, both with diamond and graphite, showed that 12 parts of carbon furnished 
44 parts of carbonic acid gas, and consumed, therefore, 32 parts of oxygen. 

A convenient arrangement for burning a diamond in oxygen 
is shown in fig. 56. The diamond is supported in a short helix 
of platinum wire A, which is attached to the copper wires B B, 
passing through the cork C, and connected with the terminal 
wires of a Grove's battery of five or six cells. The globe having 
been filled with oxygen by passing the gas down into it till a 
match indicates that the excess of oxygen is streaming out of 
the globe, the cork is inserted, and the wires connected with 
the battery. When the heat developed in the platinum coil, by 
the passage of the current, has raised the diamond to a full red 
heat, the connexion with the battery may be interrupted, and the diamond will 
continue to burn with steady and intense brilliancy. 

To an observer unacquainted with the satisfactory nature of this de- 
monstration, it would appear incredible that the transparent diamond, so 
resplendent as to have been reputed to emit light, should be identical in 
its chemical composition with graphite (plumbago or black lead) from 
which, in external appearance, it differs so widely. For this difference is 
not confined to their colour ; in crystalline form they are not in the least 
alike, the diamond occurring generally in octahedral crystals, while gra- 
phite is found either in amorphous masses (that is, having no definite 
crystalline form), or in six-sided plates which are not geometrically allied 
with the form assumed by the diamond. Carbon, therefore, is dimorphous, 
or occurs in two distinct crystalline forms. Even in weight, diamond and 
graphite are very dissimilar, the former having an average specific gravity 
of 3-5 and the latter of 2*3. Again, a crystal of diamond is the hardest 



COMBUSTION OF DIAMOND. 63 

of all substances, whence it is used for cutting and for writing upon glass, 
but a mass of graphite is soft and easily cut with a knife. The diamond 
is a non-conductor of electricity, but the conducting power of graphite 
renders it useful in the electrotype process. 

Diamonds are chiefly obtained from Golconda, Borneo, and the Brazils. 
They usually occur in sandstone rock or in mica slate. The hardness of 
the diamond renders it necessary to employ diamond-dust for the purpose 
of cutting and polishing it, which is effected with the aid of a revolving 
disk of steel, to the surface of which the diamond-dust is applied in the 
form of a paste made with oil. The crystal in its natural state is best 
fitted for the purpose of the glazier, for its edges are usually somewhat 
curved, and the angle formed by these cuts the glass deeply, while the 
angle formed by straight edges, like those of an ordinary jeweller's dia- 
mond, is only adapted for scratching or writing upon glass. Drills with 
diamond points have been employed in tunnelling through hard rocks. 
The diamond-dust used for polishing, &c, is obtained from a dark amor- 
phous diamond found at Bahia in the Brazils; 1000 ounces annually are 
said to have been occasionally obtained from this source. When burnt, 
the diamond always leaves a minute proportion of ash of a yellowish 
colour in which silica and oxide of iron have been detected. A genuine 
diamond may be known by its combining the three qualities of extreme 
hardness, enabling it to scratch hardened steel, high specific gravity 
(3*52), and insolubility in hydrofluoric acid. Sapphire (A1 2 3 ) is nearly 
as hard as diamond, but its specific gravity is about 4. 

Although the diamond, when preserved from contact with the air, may 
be heated very strongly in a furnace, without suffering any change, it is 
not proof against the intense heat of the discharge taking place between 
two carbon points attached to the terminal wires of a powerful galvanic 
battery. If the experiment be performed in a vessel exhausted of air, the 
diamond becomes converted into a black coke-like mass which closely 
resembles graphite in its properties. 

Graphite always leaves more ash than the diamond, consisting chiefly 
of the oxides of iron and manganese, with particles of quartz, and some- 
times titanic dioxide. The purest specimens are those of compact amor- 
phous graphite from Borrowdale in Cumberland ; an inferior variety, 
imported from Ceylon, is crystalline, being composed of hexagonal plates. 
Graphite is obtained artificially in the manufacture of cast iron : in some 
cases, a portion of the carbon of the cast iron separates in cooling, in the 
form of crystalline scales of graphite, technically called kish. In the 
grey variety of cast iron these scales of graphite are diffused through the 
mass of the metal, and are left undissolved when the iron is dissolved by 
an acid. 

Graphite is far more useful than the diamond, for, in addition to its 
application in black-lead pencils, and for covering the surface of iron in 
order to protect it from rust, it is largely employed in admixture with 
clay, for the fabrication of the black-lead crucibles or blue pots, as they 
are commonly called, which are so valuable to the metallurgist for their 
power of resisting high temperatures and sudden change of temperature. 
Graphite is also sometimes employed for lubricating, to diminish friction 
in machinery, and for facing or imparting a glazed surface to gunpowder. 

(Anthracite and the other varieties of coal will be described in a 
separate section.) ; 



64 PREPARATION OF CHARCOAL. 

53. Several varieties of carbon, obtained by artificial processes, are 
employed in the arts. The most important of these are lamp black, wood 
charcoal, and animal charcoal* 

Lamp black approaches more nearly in composition to pure carbon than 
either of the others, and is the soot obtained from the imperfect combus- 
tion of resinous and tarry matters (or of highly bituminous coal), from 
which source it derives the small quantities of resin, of nitrogen, and sul- 
phur which it contains. The uses of this substance, as an ingredient of 
pigments, of printing-ink, and of blacking, depend evidently more upon 
its black colour than upon its chemical properties. 

Diamond black is a very pure variety of lamp black obtained by the 
imperfect combustion of the natural hydrocarbon gas of the Ohio petro- 
leum region. 

Spanish black is charcoal made from waste cork. 

Wood charcoal presents more features which arrest the attention of the 
chemist, as well on account of its specific properties, as of the influence 
exercised by the method adopted for obtaining it, upon its fitness for 
the particular purpose which it may be destined to serve. 

If a piece of wood be heated in an ordinary fire, it is speedily con- 
sumed, with. the exception of a grey ash consisting of the incombustible 
mineral substances which it contained ; if the experiment were performed 
in such a manner that the products of combustion of the wood could be 
collected, these would be found to consist of carbonic acid gas 
and water; woody fibre is composed of carbon, hydrogen, and oxygen 
(C 6 H 10 O 5 ), and when it is burnt, the oxygen, in conjunction with more 
oxygen derived from the air, converts the carbon and hydrogen into carbon 
dioxide and water. But if the wood be heated in a glass tube, closed at 
one end, it will be found impossible to reduce it, as before, to an ash, for 
a mass of charcoal will remain, having the same form as that of the piece 
of wood ; in this case, the oxygen of the air not having been allowed free 
access to the wood, no true combustion has taken place, but the wood has 
undergone destructive distillation, that is, its elements have arranged them- 
selves, under the influence of the high temperature, into different forms of 
combination, for the most part simpler in their chemical composition than 
the wood itself, and capable, unlike the wood, of enduring that temperature 
without decomposition; thus, it is merely an exchange of an unstable 
for a stable equilibrium of the particles of matter composing the wood. 

(Definition. — Destructive distillation is the resolution of a complex 
substance into simpler forms under the influence of heat, out of contact 
with air.) 

The vapours issuing from the mouth of the tube will be found acid to 
blue litmus paper ; they have a peculiar odour, and readily take fire on 
contact with flame. These will be more particularly noticed hereafter, 
as they contain some very useful substances. The charcoal which is left 
is not pure carbon, but contains considerable quantities of oxygen 
and hydrogen with a little nitrogen, and the mineral matter or ash of 
the wood. 

When the charcoal is to be used for fuel, it is generally prepared by 
a process in which the heat developed by the combustion of a portion 

* The term pseudo-carbons has been proposed for bodies of this description characterised 
by a high percentage of carbon, and, in many respects, simulating the element itself (Cross 
and Bevan, Phil Mag., May 1882). 



PREPARATION OF CHARCOAL. 



65 



of the wood is made to effect the charring of the rest. With this view 

the billets of wood are built up into a heap (fig. 57) around stakes driven 

into the ground, a passage 

being left so that the heap 

may be kindled in the centre. 

This mound of wood, which 

is generally from 30 to 50 feet 

in diameter, is closely covered 

with turf and sand, except for 

a few inches around the base, 

where it is left uncovered to 

give vent to the vapour of 

water expelled from the wood 

in the first stage of the process. 




Fig. 57. — Charcoal heap. 




When the heap has been kindled in the 
centre, the passage left for this purpose is carefully closed up. After the 
combustion has proceeded for some time, and it is judged that the wood is 
perfectly dried, the open space at the base is also closed, and the heap left 
to smoulder for three or four weeks, when the wood is perfectly carbonised. 

Upon an average, 22 parts of 
charcoal are obtained by this 
process from 100 of wood. 

A far more economical process 
for preparing charcoal from wood 
consists in heating it in a per- 
forated iron case or slip (F, fig. 
58) placed in an iron retort 
A, from which the gases and 
vapours are conducted by the 
pipe L into the furnace B, where 
they are consumed. 

On the small scale, the opera- 
tion may be conducted in a glass 
retort, as shown in fig. 59, where 
the water, tar, and naphtha are 
deposited in the globular receiver 
over water. 

The infusibility of the charcoal left by 
great porosity, upon which 
some of its most remarkable 
and useful properties de- 
pend. The application of 
charcoal for the purpose of 
"sweetening" fish and other 
food in a state of incipient 
putrefaction has long been 
practised, and more recently 
charcoal has been employed 
for deodorising all kinds 
of putrefying and offensive 
animal or vegetable matter. This property of charcoal depends upon its 
power of absorbing into its pores very considerable quantities of the gases, 
especially of those which are easily absorbed by water. Thus, 1 cubic 

E, 



Fig. 58.— Charcoal retort, 
and the inflammable gases are collected 



wood accounts for its 



very 




Fig. 59. 



-Distillation of wood. 



66 



ABSORPTION OF GASES BY CHARCOAL. 



inch of charcoal is capable of absorbing about 100 cubic inches of ammonia 
gas and 50 cubic inches of sulphuretted hydrogen, both which are con- 
spicuous among the offensive results of putrefaction. This condensation of 
gases by charcoal is a mechanical effect, and does not involve a chemical 
combination of the charcoal with the gas ; it is exhibited most powerfully 
by charcoal which has been recently heated to redness in a closed vessel, 
and cooled out of contact with air by plunging it under mercury. Eventu- 
ally the offensive gases absorbed by the charcoal are chemically acted on 
by the oxygen of the air in its pores. A cubic inch of wood charcoal absorbs 
nearly 10 cubic inches of oxygen, and when the charcoal containing the 
gas thus condensed is presented to another gas which is capable of under- 
going oxidation, this latter gas is oxidised and converted into inodorous 
products. Thus, if charcoal be exposed to the action of air containing 
sulphuretted hydrogen gas (H 2 S), it condenses within its pores both this 
gas and the atmospheric oxygen, which slowly converts it into sulphuric 
acid (H 2 S0 4 ). 

The great porosity of wood charcoal is strikingly exhibited by attaching a piece of 
lead to a stick of charcoal (fig. 60), so as to sink it in a cylinder of water, which is 
then placed under the receiver of the air-pump. On exhausting the air, innumerable 
bubbles will start from the pores of the charcoal, causing brisk effervescence. If a 
glass tube 16 or 18 inches long be thoroughly filled with ammonia gas (fig. 61), sup- 
ported in a trough containing mercury, and a small stick of recently calcined char- 
coal introduced through the mercury into the tube, the charcoal will absorb the 
ammonia so rapidly that the mercury will soon be forced up and fill the tube, 
carrying the charcoal up with it. On removing the charcoal, and placing it upon 
the hand, a sensation of cold will be perceived from the rapid escape of ammonia, 
perceptible by its odour. 





Fig. 60. Fig. 61. 

By exposing a fragment of recently calcined wood-charcoal under a jar filled with 
hydrosulphuric acid gas for a few minutes, so that it may become saturated with 
the gas, and then covering it with a jar of oxygen, the latter gas will act upon 
the former with such energy that the charcoal will burst into vivid combustion. 
The jar must not be closed air-tight at the bottom, or the sudden expansion may 
burst it. Charcoal in powder exposed in a porcelain crucible may also be employed 
in the same way. It should be pretty strongly heated in the covered crucible, and 
allowed to become nearly cool before being exposed to the hydrosulphuric acid. 

Charcoal prepared from hard woods absorbs the largest volume of gas. Thus log- 
wood charcoal has been found to "absorb 111 times its volume of the ammoniacal gas. 
Charcoal made from the shell of the cocoa-nut is even more absorbent, although 
its pores are quite invisible, and its fracture exhibits a semi-metallic lustre. 

As the gases which are evolved in putrefaction are of a poisonous char- 
acter, the power of wood charcoal to remove them acquires great practical 



DEODORISING AND DECOLORISING BY CHARCOAL. 



67 



importance, and is applied in very many cases ; the charcoal in coarse 
powder is thickly strewn over matters from which the effluvium proceeds, 
or is exposed in shallow trays to the air to be sweetened, as in the wards 
of hospitals, &c. It has even been placed in a flat box of wire gauze to 
be fixed as a ventilator before a window through which the contaminated 
air might have access, and respirators constructed on the same principle 
have been found to afford protection against poisonous gases and vapours. 
The ventilating openings of sewers in the streets are also fitted with 
cases containing charcoal for the same purpose. Water is often filtered 
through charcoal in order to free it from the noxious and putrescent 
organic matters which it sometimes contains. For all such uses the char- 
coal should have been recently heated to redness in a covered vessel, in 
order to expel the moisture which it at- 
tracts when exposed to the air ; and the 
charcoal which has lost its power of 
absorption will be found to regain it in 
great measure when heated to redness. 

This power of absorption which char- 
coal possesses is not confined to gases, 
for many liquid and solid substances 
are capable of being removed by that 
agent from their solution in water. This 
is most readily traced in the case of 
substances which impart a colour to the 
solution, such colour being often removed 
by the charcoal ; if port wine or infusion 
of logwood be shaken with powdered 
charcoal (especially if the latter has been 
recently heated to redness in a closed 
crucible), the liquid, when filtered through 

blotting-paper (fig. 62), will be found to have lost its colour-; the colouring 
matter, however, seems merely to have adhered to the charcoal, for it may 
be extracted from the latter by treatment with a weak alkaline liquid. 

The decolorising power of wood charcoal is very feeble in comparison 
with that possessed by bone-black or animal charcoal, which is ob- 
tained by heating bones in vessels from which the air is excluded. 
Bones are composed of about one-third of animal and two-thirds of 
mineral substances, the latter including calcium phosphate, which 
amounts to more than half the weight of the bone, and a little calcium 
carbonate. "When bone is heated, as in a retort, so that air is not 
allowed to have free access to it, the animal matter undergoes destructive 
distillation, its elements— carbon, hydrogen, nitrogen, and oxygen — 
assuming other forms, the greater part of the three last elements, together 
with a portion of the carbon, escaping in different gaseous and vaporous 
products, while a considerable proportion of the carbon remains behind, 
intimately mixed with the earthy ingredients of the bone, and con- 
stituting the substance known as animal charcoal. The great differ- 
ence between the products of the destructive distillation of bone and of 
wood deserves a passing notice. If a fragment of bone or a shaving of 
horn be heated in a glass tube closed at one end, the vapours which are 
evolved will be found strongly alkaline to test-papers, while those fur- 
nished by the wood were acid ; this difference is to be ascribed mainly 




Fig. 62. — Filtration. 



68 CAEBON. 

to the presence of nitrogen in the bone, wood being nearly free from 
that element ; it will be found to hold good, as a general rule, that the 
results of the destructive distillation of animal and vegetable matters 
containing much nitrogen are alkaline, from the presence of ammonia 
(NH 3 ) and similar compounds, while those furnished by non-nitro- 
genised substances possess acid characters : the peculiar odour which is 
emitted by the heated bone is characteristic, and affords us a test "by 
which to distinguish roughly between nitrogenised and non-nitrogenised 
bodies. 

An examination of the charred mass remaining as the ultimate result 
of the action of heat upon bone, shows it to contain much less carbon 
than that furnished by wood, for the bone-charcoal contains nearly nine- 
tenths of its weight of phosphate (with a little carbonate) of calcium ; the 
consequence of the presence of so large an amount of earthy matter must 
be to extend the particles of carbon over a larger space, and thus to 
expose a greater surface for the adhesion of colouring matters, &c. This 
may partly help to explain the very great superiority of bone-black to 
wood charcoal as a decolorising agent, and the explanation derives support 
from the circumstance, that when animal charcoal is deprived of its earthy 
matter, for chemical uses, by washing with hydrochloric acid, its decolor- 
ising power is very considerably reduced. The application of this variety 
of charcoal is not confined to the chemical laboratory, but extends to 
manufacturing processes. The sugar refiner decolorises his syrup by filter- 
ing it through a layer of animal charcoal, and the distiller employs char- 
coal to remove the f ousel oil with which distilled spirits are frequently 
contaminated. 

Carbon is remarkable, among elementary bodies, for its indisposition to 
enter directly into combination with the other elements, whence it follows 
that most of the compounds of carbon have to be obtained by indirect 
processes. This element appears, indeed, to be incapable of uniting with 
any other at the ordinary temperature, and this circumstance is occasion- 
ally turned to useful account, as when the ends of wooden stakes are 
charred before being plunged into the earth, when the action of the 
atmospheric oxygen, which, in the presence of moisture, would be very 
active in effecting the decay of the wood, is resisted by the charcoal into 
which the external layer has been converted. The employment of black- 
lead to protect metallic surfaces from rust is another application of 
the same principle. At a high temperature, however, carbon combines^ 
readily with oxygen, sulphur, and with some of the metals, and, at a 
very high temperature, even with hydrogen. The tendency of carbon to 
combine with oxygen under the influence of heat, is shown when a piece 
of charcoal is strongly heated at one point, when the carbon at this point 
at once combines with the oxygen of the surrounding air (forming car- 
bonic acid gas), and the heat developed by this combustion raises the neigh- 
bouring particles of carbon to the temperature at which the element unites 
with oxygen, and thus the combustion is gradually propagated throughout 
the mass, which is ultimately converted entirely into carbonic acid gas, 
nothing remaining but the white ash, composed of the mineral substances 
derived from the wood employed for preparing the charcoal. It is worthy 
of remark, that if charcoal had been a better conductor of heat, it would 
not have been so easily kindled, since the heat applied to any point of 
the mass would have been rapidly diffused over its whole bulk, and this 



FOEMATION OF COAL. 69 

point could not have attained the high temperature requisite for its 
ignition, until the whole mass had been heated nearly to the saare degree; 
this is actually found to be the case in charcoal which has been very 
strongly heated (out of contact with air), when its conducting power is 
greatly improved, and it kindles with very great difficulty. The calorific 
value of carbon is represented by the number 8080, that is, 1 gr. of 
carbon, when burnt so as to form carbonic acid gas, is capable of raising 
8080 grs. of water from 0° C. to 1° C. 

A given weight of charcoal will produce twice as much available heat 
as an equal weight of wood, since the former contains more actual fuel 
and less oxygen, and much of the heat evolved by the wood is absorbed 
or rendered latent in the steam and other vapours which are produced by 
the action of heat upon it. The attraction possessed by carbon for oxygen 
at a high temperature is turned to account in metallurgic operations, when 
coal and charcoal are employed for extracting the metals from their com- 
pounds with oxygen. * 

The unchangeable solidity of carbon is another remarkable feature. It 
is stated that some approach has been made, at extremely high tempera- 
tures, to the fusion and vaporisation of carbon, but it cannot be said to 
have been fairly established that this element is able to exist in any other 
than the solid form. Nor can any substance be found by the aid of 
which carbon may be brought into the liquid form by the process of 
solution ; for although charcoal gradually disappears when boiled with 
sulphuric and nitric acids, it does not undergo a simple solution, but is 
converted, as will be seen hereafter, into carbon dioxide. 

The very striking difference in properties exhibited by diamond, graphite, 
and charcoal, lead to the belief that they consist of dissimilar carbon 
molecules. The investigation of the specific heats of these three varieties 
affords some grounds for the belief that the diamond molecule consists 
of four atoms, the graphite molecule of three atoms, and the charcoal 
molecule of two atoms of carbon. 

54. Coal. — The various substances which are classed together under 
the name of coal are characterised by the presence of carbon as a largely 
predominant constituent, associated with smaller quantities of hydrogen, 
oxygen, nitrogen, sulphur, and certain mineral matters which compose the 
ash. Coal appears to have been formed by a peculiar decomposition or 
fermentation of buried vegetable matter, resulting in the separation of a 
large proportion of its hydrogen in the form of marsh-gas (CH 4 ), and 
similar compounds, and of its oxygen in the form of carbonic acid gas 
(C0. 2 ), the carbon accumulating in the residue. Thus, cellulose (C 6 H 10 O 5 ), 
which constitutes the bulk of woody fibre, might be imagined to decom- 
pose according to the equation 2C 6 H 10 O 5 = 5CH 4 + 5C0 2 + C 2 , and the 
occurrence of marsh-gas, and of the paraffin hydrocarbons of similar 
composition, as well as of carbonic acid gas, in connexion with deposits 
of coal, supports this account of its. formation. Marsh-gas and carbonic 
acid gas are the ordinary products of the fermentation of vegetable matter, 
and a spontaneous carbonisation is often witnessed in the " heating" of 
damp hay. But just as the action of heat upon wood produces a charcoal 

* Easily reducible oxides, such as oxide of lead, give carbon dioxide when heated with 
charcoal; 2PbO + C=Pb 2 +C0 2 , but oxides which are not easily reducible, such as oxide 
of zinc, give carbonic oxide ; ZnO + C = CO + Zn. 



70 



VARIETIES OF COAL. 



containing small quantities of the other organic elements, so the carbon-? 
ising process by which the plants have been transformed into coal has 
left behind some of the hydrogen, oxygen, and nitrogen ; the last, as well 
probably as a little of the sulphur, having been derived from the vegetable 
albumen and similar substances which are always present in plants. The 
chief part of the sulphur is generally present in the form of iron pyrites, 
derived from some extraneous source. The examination of a peat-bog is 
very instructive with reference to the formation of coal, as affording ex- 
amples of vegetable matter in every stage of decomposition, from that in 
which the organised structure is still clearly visible, to the black carbon- 
aceous mass which only requires consolidation by pressure in order to 
resemble a true coal. 

In some cases an important part in the formation of. coal may have 
been played by slow oxidation or decay of the vegetable matter at the 
expense of atmospheric oxygen held in solution by water; since the 
hydrogen of the compound would be removed by oxidation taking place 
at a low temperature, giving rise to a gradual increase in the percentage 
of carbon. 

The three principal varieties of coal — lignite, bituminous coal, and 
anthracite — present us with the material in different stages of carbonisa- 
tion; the lignite, or brown coal, presenting indications of organised struc- 
ture, and containing considerable proportions of hydrogen and oxygen, 
while anthracite often contains little else than carbon and the mineral 
matter or ash. The following table shows the progressive diminution in 
the proportions of hydrogen and oxygen in the passage from wood to 
anthracite : — 





Carbon. 


Hydrogen. 


Oxygen 


Wood, . . 


100 


12-18 


83-07 


Peat, . 


100 


9-85 


55-67 


Lignite, 


100 


8-37 


42-42 


Bituminous coal, . 


100 


6-12 


21-23 


Anthracite, . . 


100 


2-84 


1-74 



The relative number of atoms of C, H, and O contained in the above 
may be compared in the following formulas, which must not, however, 
be taken as representing separate chemical compounds of a definite 
character : — 



Oak, 


C l7 H 24 O n 


Cannel, 


^26-^-20^2 


Peat, 


• ^20^22^8 


Caking coal, 


• C 45 H 34 2 


Lignite, 


• C 27 H 28 7 


Authracite, . 


. C 40 H 16 O 



The combustion of coal is a somewhat complex process, in consequence 
of the re-arrangement which its elements undergo when the coal is sub- 
jected to the action of heat. 

As soon as a flame is applied to kindle the coal, the heated portion 
undergoes destructive distillation, evolving various combustible gases and 
vapours, which take fire and convey the heat to remoter portions of the 
coal. Whilst the elements of the exterior portion of coal are undergoing 
combustion, the heat thus evolved is submitting the interior of the mass 
to destructive distillation, resulting in the production of various com- 
pounds of carbon and hydrogen. Some of these products, such as marsh- 
gas (CH 4 ) and defiant' gas (C 2 H 4 ), burn without smoke, while others, 
like benzene (C 6 H 6 ) and naphthalene (C 10 H 8 ), which contain a very large 
proportion of carbon, undergo partial combustion, and a considerable 



VARIETIES OF COAL. 71 

quantity of carbon, not meeting with enough, heated oxygen in the vicinity 
to burn it entirely, escapes in a very finely divided state as smoke or 
soot, which is deposited in the chimney, mixed with a little carbonate of 
ammonia and small quantities of other products of the distillation of 
coal. When the gas has been expelled from the coal, there remains a 
mass of coke or cinder, which burns with a steady glow until the whole 
of its carbon is consumed, and leaves an ash, consisting of the mineral 
substances present in the coal. The final results of the perfect combus- 
tion of coal would be carbonic acid gas (C0 2 ), water (H 2 0), nitrogen, a little 
sulphurous acid gas (S0 2 ), and ash. The production of smoke in a fur- 
nace supplied with coal may be prevented by charging the coal in small 
quantities at a time in front of the fire, so that the highly carbonaceous 
vapours must come in contact with a large volume of heated air before 
reaching the chimney. In arrangements for consuming the smoke, hot 
air is judiciously admitted at the back of the fire, in order to meet and 
consume the heated carbonaceous particles before they pass into the 
chimney. 

The difference in the composition of the several varieties of coal gives 
rise to a great difference in their mode of burning. 

The following table exhibits the composition of representative speci- 
mens of the four principal varieties : — 

Composition of Coal. 





Lignite. 


Carbon, 


66-32 


Hydrogen, 
Nitrogen, 


5-63 
0-56 


Oxygen, 
Sulphur. 
Ash,* 


22-86 
2-36 
2-27 



Bituminous 
Coal. 


Wigan Cannel. 


Anthracite 


78-57 


80-06 


90-39 


5-29 


5-53 


3-28 


1-84' 


2-12 


0-83 


12-88 


8-09 


2-98 


0-39 


1-50 


0-91 


1-03 


270 


1-61 



100-00 100-00 100-00 100-00 

The lignites furnish a much larger quantity of gas under the action of 
heat, and therefore burn with more flame than the other varieties, 
leaving a coke which retains the form of the original coal; while bitumi- 
nous coal softens and cakes together, — a useful property, since it allows 
even the dust of such coal to be burnt, if the fire be judiciously managed. 
Anthracite (stone coal or Welsh coal) is much less easily combustible 
than either of the others, and, since it yields but little gas when heated, 
it usually burns with little flame or smoke. This variety of coal is so 
compact that it will not usually burn in ordinary grates, but is much 
employed for furnaces. (See Chemistry of Fuel.) 

Jet resembles cannel coal in composition. 

Accidents occasionally arise from the spontaneous combustion of coal, 
especially when shipped in a damp state. This appears to be due, in 
some cases, to the development of heat by the action of atmospheric 
oxygen on the iron-pyrites or coal-trasses contained in the coaL Some- 
times the coal itself may be capable of slow combination with oxygen, 
and unless due provision be made for the escape of the heat, its accumula- 
tion may raise the temperature to a dangerous degree. 

* The ash of coal consists chiefly of silica, alumina, and peroxide of iron. 



72 NATURAL SOURCES OF CARBONIC ACID GAS. 

55. Carbon is capable of combining witb oxygen in two proportions, 
forming the compounds known as carbonic oxide (CO) and carbon dioxide 
(C0 2 ). 

Carbon Dioxide or Carbonic Acid Gas. 
C0. 2 = 44 parts by weight = 2 vols. 44 grammes = 22 "38 litres. 

56. It has been already mentioned that carbonic acid gas is a com- 
ponent of the atmosphere, which usually contains about 4 volumes of 
carbonic acid gas in 10,000 volumes of air. This gas is chiefly formed by 
the operation of the atmospheric oxygen in supporting combustion and 
respiration. 

All substances used as fuel contain a large proportion of carbon, which, 
in the act of combustion, combines with the oxygen, and escapes into the 
atmosphere in the form of carbonic acid gas. 

In the process of respiration, the carbonic acid gas is formed from the 
carbon contained in the different portions of the animal frame to which 
oxygen is conveyed by the blood; the latter, in passing through the 
lungs, gives out, in exchange for the oxygen, a quantity of carbonic acid 
gas produced by the union of a former supply of oxygen with the carbon 
of the different organs to which the blood is supplied, which, as they are 
constantly corroded and destroyed by this oxidising action of the blood, are 
repaired by the supply of food taken into the body. This conversion of 
carbon of the organs into carbonic acid gas will be again referred to ; it 
will be at once evident that it must be concerned in the maintenance of 
the animal heat. 

The leaves of plants, under the influence of light, have the power of 
decomposing the carbonic acid gas of the atmosphere, the carbon of which 
is applied to the production of vegetable compounds forming portions of 
the organism of the plant, and when this dies, the carbon is restored, after 
a lapse of time more or less considerable, to the atmosphere, in the same 
form, namely, that of carbonic acid gas, in which it originally existed 
there. If a plant should have been consumed as food by animals, its 
carbon will have been eventually converted into carbonic acid gas .by 
respiration; the use of the plant as fuel, either soon after its death (wood), 
or after the lapse of time has converted it into coal, will also consign its 
carbon to the air in the form of carbonic acid gas. Even if the plant be 
left to decay, this process involves a slow conversion of its carbon into 
carbonic acid gas by the oxygen of the air.* 

Putrefaction and fermentation are also very important processes con- 
cerned in restoring to the air, in the form of carbonic acid gas, the carbon 
contained in dead vegetable and animal matter. Although, in a popular 
sense, these two processes are distinct, yet their chemical operation is of 
the same kind, consisting in the resolidion of a complex substance into 
simpler forms, produced by contact with some minute living plant or 
animal. The discussion of the true nature of the process (which is even 
now somewhat obscure) would be premature ac this stage, and it will 

* In the dark, according to Boussingault, plants evolve carbonic acid gas. He found that 
a square metre (39 '37 inches square) of oleander leaves decomposed, in sunlight, on an 
average, 1 *108 litre (67 '6 cubic inches) of carbonic acid gas every hour ; whilst the same extent 
of leaf, in the dark, emitted 0-07 litre (4*27 cubic inches) of carbonic acid gas in the hour. 
Even under the influence of light, flowers have been found to absorb oxygen and evolve 
carbonic acid gas. 



SOUECES OF CARBONIC ACID GAS. 



73 



suffice for the present to state that carbonic acid gas is one of the simpler 
forms into which the carbon is converted by the metamorphosis which 
ensues so quickly upon the death of animals and vegetables. 



The production of carbonic acid gas in combustion, 
respiration, and fermentation, may be very easily proved by 
experiment. If a dry bottle be placed over a burning wax 
taper standing on the table, the sides of the bottle will be 
covered with dew from the combustion of the hydrogen in 
the wax ; and if a little clear lime-water be shaken in the 
bottle, the milky deposit of calcium carbonate will indi- 
cate the formation of the carbonic acid gas. 

By arranging two bottles, as represented in fig. 63, and 
inspiring through the tube A, air will bubble through the 
lime-water in B, before entering the lungs, and will then 
be found to contain too little carbonic acid gas to produce 
a milkiness, but on expiring the air, it will bubble through 
C, and will render the lime-water in this bottle very dis- 
tinctly turbid. 

If a little sugar be dissolved in eight or ten times its 
weight of warm (not hot) water, in the flask A (fig. 64), 
and a little dried yeast, previously rubbed down with water, 
added, fermentation will commence in the course of an 
hour or less, and carbonic acid gas may be collected in the 
jar B. 




Fis. 63. 



57. In the mineral kingdom, carbon dioxide is pretty abundant. The 
gas issues from the earth in some places in considerable quantity, as 
at Nauheim, where there 
is said to be a spring ex- 
haling about 1,000,000 lbs. 
of the gas annually. Many 
spring waters, those of 
Seltzer and Pyrmont, for 
example, are very highly 
charged with the gas. 

But it occurs in far larger 
quantity in the immense 
deposits of limestone, mar- 
ble, and chalk, which com- 
pose so large a portion of 
the crust of the globe. 
Calcium carbonate is also 
met with in the animal 
kingdom. Oyster - shells Fig- 6 ^. 

contain 98 per cent, aud egg-shells 97 per cent, of it, and pearls contain 
about two-thirds of their weight. 

The expulsion of the carbonic acid gas from limestone (CaC0 3 ) forms 
the object of the process of lime burning, by which the large supply of lime 
(CaO) is obtained for building and other purposes. But if it be required 
to obtain the carbonic acid gas without regard to the lime, it is better to 
decompose the carbonate with an acid. 

Preparation of carbonic acid gas. — The form of the calcium carbonate, 
and the nature of the acid employed, are by no means matters of indifference. 
If dilute sulphuric acid be poured upon fragments of marble, the effer- 
vescence which occurs at first soon ceases, for the surface of the marble 




74 



PROPERTIES OF CARBONIC ACID GAS. 



becomes coated with the nearly insoluble calcium sulphate, by which it is 
protected from the further action of the acid — 



CaCO, 

Marble. 



h H 2 S0 4 - 

Sulphuric acid. 



CaSO d + H 9 + CO, 



Sulphate of 
lime. 



if the marble be finely powdered, or if powdered chalk be employed, each 
rmrticle of the carbonate will be acted upon. When lumps of calcium 
carbonate are acted upon by hydrochloric acid, there is no danger that any 



will escape the action of the 
one of the most soluble salts- 



acid, for the calcium chloride produced is 



CaCO, + 2HC1 = CaCl 9 + H 9 + CO, 



Marble. 



Hydrochloric 
acid. 



Calcium 
chloride. 



For the ordinary purposes of experiment, carbonic acid gas is most 
easily obtained by the action of dilated hydrochloric acid upon small 

fragments of marble (fig. 65), the latter 
being covered with water, and hydro- 
chloric acid poured in through the funnel- 
tube. The gas may be collected by down- 
ward displacement. 

58. Properties of carbon dioxide. — Car- 
bonic acid gas is invisible, like the gases 
already examined, but is distinguished by 
a peculiar pungent odour, as is perceived 
in soda-water. It is more than half as 
heavy again as atmospheric air, its specific 



Fig. 




-Preparation of carbonic 
acid gas. 

gravity being 1*529, which causes its accumulation near the floor of such 
confined spaces as the Grotto del Cane, where it issues from fissures in 
the rock. 




Fig. 66. 

The high, specific gravity of carbonic acid gas may be shown by pouring it into 
a light jar attached to a balance, and counterpoised by a weight in the opposite scale 
(fig. 66). 



EFFECT OF CARBONIC ACID GAS ON FLAME. 



75 



<^*" 




Another favourite illustration consists in floating a soap-bubble on the surface of a 
layer of the gas generated in the large jar (fig. 67), by pouring diluted sulphuric acid 
upon a few ounces of chalk made into a thin cream with water. 

If a small balloon, made of collodion, be 
placed in the jar A (fig. 68), it will ascend on 
the admission of carbonic acid gas through the 
tube B. 

If smouldering brown paper be held at the 
mouth of a jar, like that in fig. 68, the smoke 
will float upon the surface of the carbonic acid 
gas, and will sink with it on removing the 
stopper. 

The power which carbonic acid gas 
possesses of extinguishing flame is very 
important, and has received practical 
application in the case of burning mines 
which must otherwise have been flooded 
with wat3r.* Many attempts have also been made from time to time to 
employ this gas for subduing ordinary conflagrations, but their success has 
hitherto been, very partial. It will be remembered that pure nitrogen is 
also capable of extinguishing the flame of a taper, but a large proportion 




Fig. 67. 





Fig. 68. 



Fig. 69. 



of this gas may be present in air without affecting the flame, whereas a 
taper is extinguished in air containing one-eighth of its volume of car- 
bonic acid gas, and is sensibly diminished in brilliancy by a much 
smaller proportion of the gas. 

The power of extinguishing flame, conjoined with the high density of carbonic 
acid gas, admits of some very interesting illustrations. 

Carbonic acid gas may be poured from some distance upon a candle, and will extin- 
guish it at once. By employing a gutter, made of thin wood or stiff paper, to conduct 
the gas to the flame, it may be extinguished from a distance of several feet. 

A large torch of blazing tow may be plunged beneath the surface of the carbonic 
acid gas in the jar (fig. 67). 

* All gases which take no part in combustion may extinguish flame, even in the presence 
of air, by absorbing heat and reducing the temperature below the burning point. 



76 



EFFECT OF CARBONIC ACID GAS ON ANIMALS. 




Carbonic acid gas may be raised in a glass bucket (fig. 69) from a large jar, and 
poured into another jar, the air in which has been previously tested with a taper. 
A wire stand with several tapers fixed at different levels may be placed in the jar 
A (fig. 70), and carbonic acid gas gradually admitted 
through a flexible tube connected with the neck of 
the jar, from the cistern B, a hole in the cover of 
which allows air to enter it as the gas flows out ; 
the flame of each taper will gradually expire as the 
surface of the gas rises in the jar. 

A jar of oxygen may be placed over a jar of carbonic 
acid gas, as shown in fig. 53, and a taper let down 
through the oxygen, in which it will burn brilliantly, 
into the carbonic acid gas, which extinguishes it, and 
if it be quickly raised again into the oxygen, it will 
rekindle with a slight detonation. This alternate 
extinction and rekindling may be repeated several 
times. 

On account of this extinguishing power of 
carbonic acid gas, a taper cannot continue to 
burn in a confined portion of air until it has 
exhausted the oxygen, but only until its com- 
bustion has produced a sufficient quantity of 
Fig. 70. carbon dioxide to extinguish the flame.* 

To. demonstrate this, advantage may be taken of the circumstance that phosphorus 
will continue to burn in spite of the presence of carbonic acid gas. Upon the stand 
A (fig. 71) a small piece of phosphorus is placed, and a 
taper is attached to the stand by a wire. The cork B 
fits air-tight into the jar, and carries a piece of copper 
wire bent so that it may be heated by the flame of the 
taper. A little water is poured into the plate to prevent 
the entrance of any fresh air. If the taper be kindled, 
and the jar placed over it, the flame will soon die out ; 
and on moving the jar so that the hot wire may touch 
the phosphorus, its combustion will show that a con- 
siderable amount of oxygen still remains. 

In the same manner, an animal can breathe a 
confined portion of air only until he has charged it with so much carbonic 
acid gas that the hurtful effect of this gas begins to be felt, a considerable 
quantity of oxygen still remaining. 

If the air contained in the jar A (fig. 72), standing over water, be breathed two or 
three times through the tube B, a painful sense of oppression will soon be felt in 
consequence of the accumulation of carbonic acid gas. The air may thus be charged 
with 10 volumes of carbonic acid gas in 100 volumes, the oxygen becoming reduced 
to about one-half its original quantity. By immersing a deflagrating spoon C, 
containing a piece of burning phosphorus, and having a lighted taper attached, it 
may be shown that although there is enough carbonic acid gas to extinguish the 
taper, the oxygen is not exhausted, for the phosphorus continues to burn rapidly. 

Carbonic acid gas is not poisonous when taken into the stomach, but 
acts most injuriously when breathed, by offering an obstacle to that escape 
of carbonic acid gas, by diffusion, from the blood of the venous circu- 
lation in the lungs, and its consequent replacement by "the oxygen neces- 
sary to arterial blood. Any hindrance to this interchange must impede 
respiration, and such hindrance would, of course, be afforded by carbonic 
acid gas present in the air inhaled, in proportion to its quantity. The 
difference in constitution and temperament in individuals makes it 

* When the taper is extinguished, the air contains in 100 volumes 18| volumes of 
oxygen and 2^ volumes of carbonic acid gas. 




Fig. 71. 



PRINCIPLES OF VENTILATION. 



77 




Fig. 72. 



impossible that any exact general rule should be laid down as to the 
precise quantity of carbonic acid gas which may be present in air without 
injury to respiration, but it may be safely asserted that it is not advisable 
to breathe for any length of time in air containing more than 10 1 00 th (01 
per cent.) of its volume of carbonic 
acid gas. The air of a room contains 
too much carbonic acid gas, if half a 
measured ounce of lime-water becomes 
turbid when shaken in a half-pint 
bottle of the air. 

There appears to be no immediate 
danger, however, until the carbonic 
acid gas amounts to glroth (0*5 per 
cent.), when most persons are attacked 
by the languor and headache attending 
the action of this gas. A larger 
proportion of carbonic acid gas pro- 
duces insensibility, and air containing 
J^th of its volume causes suffocation. 
The danger in entering old wells, 
cellars, and other confined places, is 
due to the accumulation of this gas, 
either exhaled from the earth or pro- 
duced by decay of organic matter. The ordinary test applied to such 
confined air by introducing a candle is only to be depended upon if the 
candle burns as brightly in the confined space as in the external air ; 
should the flame become at all dim, it would be unsafe to enter, for 
experience has shown that combustion may continue for some time in an 
atmosphere dangerously charged with carbonic acid gas. 

The accidents from choke damp and after damp in coal mines, and 
from the accumulation, in brewers' and distillers' vats, of the carbonic 
acid gas resulting from fermentation, are also examples of its fatal effect. 

The air issuing from the lungs of a man at each expiration contains 
from 3*5 to 4 volumes of carbonic acid gas in 100 Volumes of air, and 
could not, therefore, be breathed again without danger. The total amount 
of carbonic acid gas evolved by the lungs and skin amounts to about 0*7 
cubic foot per hour. In order that it may be breathed again without 
inconvenience, this should be distributed through at least 140 cubic feet 
of fresh air, or a space measuring 5 '2 feet each way. Hence the necessity 
for a constant supply of fresh air by ventilation, to dilute the carbonic 
acid gas to such an extent that it may cease to impede respiration. This 
becomes the more necessary where an additional quantity of carbonic 
acid gas is supplied by candles or gas-lights. An ordinary gas burner 
consumes at least 3 cubic feet of gas per hour, and produces about 
1 -7 cubic foot of carbonic acid gas. Fortunately, a natural provision for 
ventilation exists in the circumstance that the processes of respiration and 
combustion, which contaminate the air, also raise its temperature, thus 
diminishing its specific gravity by expansion, and causing it to ascend 
and give place to fresh air. Hence the vitiated air always accumulates 
near the ceiling of an apartment, and it becomes necessary to afford it an 
outlet by opening the upper sash of the window, since the chimney 
ventilates immediately only the lower part of the room. 



PRINCIPLES OF VENTILATION. 



These principles may be illustrated by some very simple experiments. 
Two quart jars (fig. 73) are filled with carbonic acid gas, and after being tested with 
a taper, a 4 oz. flask is lowered into each, one flask containing cold and the other hot 

water. After a few minutes the jar with 
the cold flask will still contain enough 
carbonic acid gas to extinguish the taper, 
whilst the air in the other jar will support 
combustion brilliantly. 

A tall stoppered glass jar (fig. 74) is 

placed over a stand, upon which three 

lighted tapers are fixed at different heights. 

The vitiated air, rising to the top of the 

jar, will extinguish the uppermost taper 

first, and the others in succession. By 

quickly removing the stopper and raising 

the jar a little before the lowest taper has 

Fig. 73. expired, the jar will be ventilated and the 

taper revived. 

A similar jar (fig. 75), with a glass chimney fixed into the neck through a cork or 

piece of vulcanised tubing, is placed over a stand with two tapers, one of which is 

near the top of the jar, and the other beneath the aperture of the chimney ; if a 








Fig. 74. 



Fig. 75. 



crevice for the entrance of air be left between the jar and the table, the lower taper 
will continue to burn indefinitely, whilst the upper one will soon be extinguished by 
the carbonic acid gas accumulating around it. 

In ordinary apartments, the incidental crevices of the doors and windows 
are depended npon for the entrance of fresh air, whilst the contaminated 
air passes out by the chimney ; but in large buildings special provision 
must be made for the two air currents. In mines this becomes the more 
necessary, since the air receives much additional contamination by the 
gases (marsh-gas and carbon dioxide) evolved from the workings, and by 
the smoke occasioned in blasting with gunpowder. Mines are generally 
provided with two shafts for ventilation, under one of which (the upcast 
shaft) a fire is maintained to produce the upward current, which carries off 
the foul air, whilst the fresh air descends by the other {downcast shaft). 
The current of fresh air is forced by wooden partitions to divide itself, 
and to pass through every portion of the workings. 

The operation of such provisions for ventilation is easily exhibited. 

A tall jar (fig. 76) is fitted with a ring of cork, carrying a wide glass chimney (A). 
If this be placed over a taper standing in a plate of water, the accumulation of vitiated 
air will soon extinguish the taper ; but if a second chimney (B), supported in a wire 
ring, be placed within the wide chimney, fresh air will enter through the interval 
between the two, and the smoke from a piece of brown paper will demonstrate the 
existence of the two currents, as shown by the arrows. 



EFFERVESCING DRINKS. 



79 



A small box (fig. 77) is provided with a glass chimney at each end. In one of these 
(B) representing the upcast shaft, a lighted taper is suspended. A piece of smoking 
brown paper may be held in each chimney to show the direction of the current. On 
closing A with a glass plate, the taper in B will be extinguished, the entrance of fresh 
air being prevented. By breathing gently into A the taper will also be extinguished. 
The experiment may be varied by pouring carbon dioxide and oxygen alternately into 
A, when the taper will be extinguished and rekindled by turns. 





Fig. 76. 



Fig. 77. 



A pint bell-jar (fig. 78) is placed over a taper standing in a tray of water. If a 
chimney (a common lamp-glass) be placed on the top of the jar, the flame of the 
taper will gradually die out, because no provision exists for the establishment of the 
two currents, but on dropping a piece of tin-plate or card-board into the chimnev 
so as to divide it, the taper will be revived, and the smoke from the brown paper will 
distinguish the upcast from the downcast shaft. 

If a little water "be poured into a wide-mouthed bottle of carbonic 
acid gas, and the bottle be then firmly closed by the palm of the hand, it 
will be found, on shaking the bottle violently, that the gas is absorbed, 
and the palm of the hand is sucked into the bottle. The presence of 
carbonic acid in the solution may be proved by 
pouring it into lime-water, in which it will produce 
a precipitate of calcium carbonate, redissolved by a 
further addition of the solution of carbonic acid. 

One pint of water shaken in a vessel containing 
carbonic acid gas, at the ordinary pressure of the atmo- 
sphere, will dissolve about one pint of the gas, equal 
in weight to nearly 16 grains. If the gas be confined 
in the vessel under a pressure equal to twice or thrice 
that of the atmosphere — that is, if twice or thrice the 
quantity of gas be compressed into the same space, 
the water will still dissolve one pint of the gas, but 
the weight of this pint will now be twice or thrice that 
of the pint of uncompressed gas, so that the water will 
have dissolved 32 or 48 grains of the gas, accordingly Fig. 78. 

as the pressure had been doubled or trebled. As soon, however, as the 
pressure is removed, the compressed carbonic acid gas will resume its 
former state, with the exception of that portion which the water is 
capable of retaining in solution under the ordinary pressure of the atmo- 
sphere. Thus if the water had been charged with carbonic acid gas under 




80 LIQUEFACTION OF CARBONIC ACID GAS. 

a pressure equal to thrice that of the atmosphere, and had therefore 
absorbed 48 grains of the gas, it would only retain 16 grains when the 
pressure was taken off, allowing 32 grains to escape in minute bubbles, 
producing the appearance known as effervescence. This affords an ex- 
planation of the properties of soda-water, which is prepared by charging 
water with carbonic acid gas under considerable pressure, and rapidly 
confining it in strong bottles. As soon as the resistance offered by the 
cork to the expansion of the gas is removed, the excess above that which 
the water can hold in solution at the ordinary pressure of the air, escapes 
with effervescence. In a similar manner the waters of certain springs 
become charged with carbonic acid gas, under high pressure, beneath the 
surface of the earth, and when, upon their rising to the surface, this 
pressure is removed, the excess escapes with effervescence, giving rise to 
the sparkling appearance and sharp flavour which renders spring water 
so agreeable. On the other hand, the waters of lakes and rivers are 
usually flat and insipid, because they hold in solution so small a quantity 
of carbonic acid gas. 

The solution of carbon dioxide in water is believed by many chemists 
to contain the true carbonic acid H 2 C0 3 , for C0 2 + H 2 = H 2 C0 3 , but 
there is no direct evidence in support of this view. 

The sparkling character of champagne, bottled beer, &c, is due to the 
presence in these liquids of a quantity of carbonic acid gas which has been 
generated by fermentation, subsequent to bottling, and has therefore been 
retained in the liquid under pressure. In the case of Seidlitz powders 
and soda-water powders, the effervescence caused by dissolving them 
in water is due to the disengagement of carbonic acid gas, by the action 
of the tartaric acid, which composes one of the powders, upon the 
bicarbonate of soda, producing tartrate of soda and carbonic acid gas. 
In the dry state these powders may be mixed without any chemical 
change, but the addition of water immediately causes the effervescence. 
Baking powders are mixtures of this kind, being used for imparting 
lightness and porosity to bread and cakes, by distending the dough with 
bubbles of carbonic acid gas. 

The solubility of carbonic acid in water is of great importance in the 
chemistry of nature ; for this acid, brought down from the atmosphere 
dissolved in rain, is able to act chemically upon rocks, such as granite, 
which contain alkalies — the carbonic acid attacking these, and thus 
slowly disintegrating or crumbling down the rock, an effect much assisted 
by the mechanical action of the expansion of freezing water in the inter- 
stices of the rock. It appears that soils are thus formed by the slow 
degradation of rocks, and when these soils are capable of supporting 
plants, the solution of carbonic acid is again of service, not only as a 
direct food, by providing the plant with carbon through its roots, but as 
a solvent for certain portions of the mineral food of the plant (such as 
calcium phosphate), which pure water could not dissolve, and which the 
plant cannot take up except in the dissolved state. 

59. Although carbon dioxide retains the state of gas under all tem- 
peratures and pressures to which it is commonly exposed, it is capable of 
assuming the liquid and even the solid state. 

At about the ordinary temperature (63° F.) carbonic acid gas is con- 
densed, by a pressure of 54 atmospheres (800 lbs. per square inch), to a 



LIQUEFACTION OF CAEBONIC ACID GAS. 



81 



colourless liquid of sp. gr. 0*83 (water =1), and at a temperature of 
- 70° F. (70° below the zero, or 102° below the freezing-point F.) becomes 
a transparent mass of solid carbon dioxide resembling ice. 

If the temperature of the gas be reduced to 32° F. a pressure of 35 
atmospheres only will suffice to liquefy it. 

The experiments of Andrews upon the liquefaction of carbon dioxide show that, in 
causing the liquefaction of gases, increase of pressure is not always equivalent to 
reduction of temperature, but that there exists a particular temperature for each gas 
above which no amount of pressure is able to liquefy it, and at this particular tempera- 
ture, the critical point, the gas is wavering between the gaseous and the liquid state, 
so that "the gaseous and liquid states are only widely separated forms of the same 
condition of matter, and may be made to pass into one another by a series of grada- 
tions so gentle, that the passage shall nowhere present any interruption or breach of 
continuity." It was found to be impossible to liquefy carbon dioxide above a tem- 
perature of 88° F., even by a pressure of 109 atmospheres ; but, at this high pressure 
the gas ceased to obey the law that the volume of a gas is inversely as the pressure, 
for instead of occupying y^ of its original volume, it had been reduced to T ^. On 
cooling the gas thus compressed, it liquefied suddenly, and not gradually as in the 
case of a vapour under ordinary pressure. The gas in this condition, when subjected 
to very small variations of temperature or pressure, exhibits curious flickering move- 
ments, resembling the effect produced by the ascent of columns of heated air through 
colder strata. 

Even at 55° F. , a pressure of 48 "89 atmospheres reduced the gas (not to ^ but) to 
-g T of its original volume without liquefying it, but at this point an additional pressure 
of only 2V atmosphere suddenly liquefied one half of the gas. 

A small specimen of liquid carbon dioxide is easily prepared. A strong tube of green 
glass (A, fig. 79) is selected, about 12 inches long, y% inch diameter in the bore, and 
Yt inch thick in the walls. 

With the aid of the blowpipe a ^__^ 

flame this tube is softened 
and drawn off at about an 
inch from one end, as at B, 
which is thus closed (C). ( 
This operation should be per- 
formed slowly, in order that 
the closed end may not be 
much thinner than tKe walls 
of the tube. When the tube 
has cooled, between 30 and 
40 grs. of powdered bicar- 
bonate of ammonia' (ordinary 
sesquicarbonate which has 
crumbled down) are tightly 
rammed into it with a glass 
rod. This part of the tube is 
then surrounded with a few 
folds of wet blotting-paper to 
keep it cool, and the tube is 
bent, just beyond the carbon- 
ate of ammonia, to a somewhat 
obtuse angle (D). The tube 
is then softened at about an 
inch from the open end, and 
drawn out to a narrow neck (E) 
is poured down a funnel-tube 



L 




Fig. 79. 



through which a measured drachm of oil of vitriol 
so as not to soil the neck, which is then carefully 
drawn out and sealed by the blowpipe flame, as at F. The empty space in the tube 
should not exceed £ cubic inch. 

When the tube is thoroughly cold, it is suspended by strings in such a position 
that the operator, having retired behind a screen at some distance, may reverse the 
tube, allowing the acid to flow into the limb containing the carbonate of ammonia ; 
or the tube may be fixed in a box which is shut up, and reversed so as to bring the 
tube into the required position. 

If the tube be strong enough to resist the pressure, it will be found, after a few 

F 



82 



LIQUEFACTION OF CARBONIC ACID GAS. 



hours, that a layer of liquid carbon dioxide has been formed upon the surface of the 
solution of ammonium sulphate. By cooling the empty limb in a mixture of pounded 
ice and salt, or of hydrochloric acid and sodium sulphate, the liquid can be made to 
distil itself over into this limb, leaving the ammonium sulphate in the other. 

Fig. 80 represents Thilorier's apparatus for the preparation of several pints of 
liquid carbon dioxide, g is a strong ivrought-iron generator of gas in which 2 lbs. of 
bicarbonate of soda are well stirred with 4 pints of water at 100° F. Half a pint of 
oil of vitriol is poured into a brass tube which is dropped upright into the generator, 
as shown by the dotted lines in the figure, which also indicate the level of the liquid 
in the generator. The head of the generator is then firmly screwed on, with the help 
of the spanners represented in the figure, and the stopcock* firmly closed by turning 
the wheel w. The generator is then turned over and over on its trunnions resting 
upon the stand 5, for ten minutes, so that the whole of the sulphuric acid may be 
mixed with the solution of bicarbonate of soda. The generator is then connected, by 
the copper tube t, with the strong wrought-iron receiver r, the stopcock of which 
is attached to a tube passing down to the bottom of the vessel. The stopcock of the 
receiver is then opened, by turning the wheel v, and afterwards that of the generator. 

The condensed gas then passes over into the receiver. After two or three minutes 
the stopcocks are again closed, the generator detached, the waste gas blown out 
through the stopcock, the head unscrewed, and the generator emptied and recharged. 
After the operation has been repeated three times, the pressure in the receiver will 




Fig. 80. — Liquefaction of carbonic acid. 

be found to have liquefied some of the carbon dioxide, and after seven charges, the 
receiver is nearly filled with the liquid acid. The tube t is then unscrewed from the 
receiver, and replaced by the nozzle n. If the stopcock be then slightly opened, a 
stream of the liquid will be forced up the tube, and, issuing into the air, will congeal 
by its own evaporation into an opaque white spray of solid carbon dioxide. 

' In order to collect the solid, the box shown as b is employed. This is made of 
brass, and furnished with strong flanges by which the cover "is secured to it. The 
handles of the box are made of wood or gutta-percha, and are hollow, with brass tubes 
passing through them to allow of the escape of the gas, the ends of the tubes within 
the box being covered by perforated plates which prevent the escape of the solid. 
The box and its cover having been fitted together, the nozzle of the receiver r is 
inserted into a short tube projecting from the side of the box, and whilst one operator 
holds the box firmly by the handles, another gradually opens the stopcock by turning 

* These stopcocks are steel screws with conical points fitting into gun-metal sockets. 
Leaden washers are employed to secure the tightness of the joints between the iron vessels 
and their heads, which are made of gun-metal. 



SOLIDIFIED CARBONIC ACID GAS. 



83 




the wheel v. A stream of the liquid is at once forced into the box, where it strikes 

against a curved brass plate arranged so as to force it to pass all around the inside of 

the box ; about seven-eighths of it evaporate as -gas, which rushes out through the 

tubular handles, and the rest is found in the box in a solid state 

resembling snow. It should be quickly shaken on to a sheet of 

paper, and emptied into a beaker placed within a larger beaker, 

the interval being filled up by flannel. By covering the beaker 

with a dial glass, the solid may be kept for some time. The 

box becomes intensely cold, and condenses the moisture of the 

air to a thick layer of hoar frost, and if it be dipped into water 

it becomes coated with ice. 

The solid carbon dioxide evaporates without melting, for its 
melting point is -85° F., and its own evaporation keeps it at 
- 125° F. It produces a sharp sensation of cold when placed upon 
the hand, and if pressed into actual contact with the skin, causes 
a painful frost-bite. Its rapid evaporation may be shoAvn by 
placing a few fragments on the surface of water in the globe 
(fig. 81), which has a tube passing down to the bottom, through 
which the pressure of the carbonic acid gas forces the water to 
a considerable height. 

The solid carbon dioxide is soluble in ether, and it evaporates 
from this solution far more rapidly, because the liquid is a better 
conductor of heat than the highly porous solid, and abstracts 
heat more rapidly from surrounding objects. 

If a layer of ether be poured upon water, and some solid 
carbon dioxide be thrown into it, the water is covered with a 
layer of ice. 

On immersing the bulb of a thermometer into the solution of solid carbon dioxide 
in ether, the mercury becomes solid, and the bulb may be hammered out into a disk. 

By placing a piece of filter-paper in an evaporating dish, pouring a pound or so of 
mercury into it, immersing a wire turned into a flat spiral at the end, covering the 
mercury with ether, and throwing in some solid carbon dioxide, the mercury may 
soon be frozen into a cake. If this be suspended by the wire in a vessel of water, 
the mercury melts, descending in silvery streams to the bottom of the vessel, leaving 
a cake of ice on the wire, with icicles formed during the descent of the mercury. 
This experiment is rendered more effective by using an inverted gas-jar, to the 
neck of which is attached, by a perforated cork, a test-tube to catch the mercury. 
The round lid of a cardboard box gives a nice disk of frozen mercury. 

Even in a red hot vessel, with prompt manipulation, the mercury may be solidified 
by the solution of solid carbon dioxide in ether. For this purpose a platinum dish 
is heated to redness over a large Bunsen burner, a few lumps of carbon dioxide are 
thrown into it, upon these is held a copper or platinum dish containing the mercury, 
in which is also held a wire to serve as a handle for withdrawing the mercury. Some 
more carbon dioxide is thrown upon the mercury, and ether is spirted on to it from 
a small w T ashing-bottle. One or two additions of the carbon dioxide and ether 
alternately will freeze the mercury, which may be withdrawn from the flames by the 
wire handle. 

The temperature produced by the evaporation of the solid carbon dioxide dissolved 
in ether is estimated at - 150° F. 

60. Carbonic acid gas may be separated from most other gases by the 
action of potash, which absorbs it, forming potassium carbonate. The 
proportion of carbonic acid gas is inferred, either from the diminution in 
volume suffered by the gas when treated with potash, or from the increase 
of weight of the latter. 

In the former case the gas is carefully measured over mercury (fig. 82), with due 
attention to temperature and barometric pressure, and a little concentrated solution 
of potash is thrown up through a curved 2) ipettc or syringe, introduced into the orifice 
of che tube beneath the surface of the mercury. The tube is gently shaken for a 
few seconds to promote the absorption of the gas, and, after a few minutes' rest, the 
diminution of volume is read off. Instead of solution of potash, damp potassium 
hydrate in the solid state is sometimes introduced, in the form of small sticks or 
balls attached to a wire. To determine the weight of carbonic acid gas in a gaseous 



84 



ANALYSIS OF ORGANIC SUBSTANCES. 



mixture, the latter is passed through a bulb-apparatus (C, fig. 83), containing a strong 
solution of potash, arid weighed before and after the passage of the gas. When the 
proportion of carbonic acid in the gas is small, it is usual to attach to the bulb-appa- 
ratus a little tube, containing solid 
potash, or calcium chloride, or pumice- 
stone moistened with sulphuric acid, for 
the purpose of retaining any vapour of 
water which the large volume of unab- 
solved gas might carry away in passing 
through the solution of potash. 

61. Ultimate organic analysis. — 
It is necessary to determine in the 
above manner the weight of car- 
bonic acid gas, in order to ascertain 
the proportion of carbon present 
in organic substances. For this 
purpose an accurately weighed 
quantity (usually from 7 to 10 
grains) of the organic substance is 
very carefully mixed with some 
compound from which it can obtain 
oxygen at a high temperature, such 
as copper oxide (CuO) or lead chromate (PbCr0 4 ), care being taken to 
employ a large excess of the oxidising agent. The mixture is introduced 
into a combustion-tube of German glass (which is free from lead and noted 
for its infusibility) of the form shown in A (fig. 83). This tube is 
provided with a small tube B, containing calcium chloride, which 
is connected by a tube of caoutchouc with the potash bulbs C. On 
gradually heating the tube in a charcoal furnace, or over a properly 
constructed gas-burner, the hydrogen and carbon contained in the 
organic substance are converted respectively into water and carbonic 
acid gas, by the oxygen derived from the lead chromate or copper 




Fig. 82. 




Apparatus for organic analysis. 



oxide. The water is absorbed by the calcium chloride in B, and 
the increase of weight in this tube will indicate the quantity of water 
formed in the combustion, whilst that of the potash bulbs will show the 
weight of the carbonic acid gas. When the whole length of the tube 
is red hot, and no more gas passes through the bulbs, the sealed point D 
of the tube is broken off, and air drawn through by applying suction at E, 
in order to sweep out the last traces of water and carbonic acid gas into 
the calcium chloride and potash. Sometimes the organic substance is 
heated in a little platinum tray, placed within a glass tube, through which 
a stream of pure oxygen is passed, the products of combustion being 



EMPIRICAL AND RATIONAL FORMULA. 85 

afterwards made to pass over red hot copper oxide, to convert any 
carbonic oxide into carbon dioxide, and collected for weighing as 
before. 

When the organic substance contains carbon, hydrogen, and oxygen, 
the weight of this last is inferred by subtracting the weights of the carbon 
and hydrogen from that of the substance. As an example of the ultimate 
analysis of an organic substance, the results of an analysis of oxalic acid 
are here given — 

10 grs. of oxalic acid, dried at 212° F., gave 9 - 78 grs. of carbon dioxide 
and 2-00 grs. of water. 

C0 9 C C0 2 

44 • : 12 : : 9'78 : x 
x = 2'67 grs. of carbon in 10 grs. of oxalic acid. 

H 9 H 2 H 9 

18 : 2 : : 2'00 : y 
y = 0'22 gr. of hydrogen in 10 grs. of oxalic acid. 

It having been ascertained by preliminary experiments that oxalic acid 
contains only carbon, hydrogen, and oxygen, 10 (oxalic acid) minus 2*89 
(carbon and hydrogen) = 7 "11 grs. of oxygen in 10 grs. of oxalic acid. 
It appears, therefore, that 

10 grs. of oxalic acid contain 
2*67 „ carbon, 
0*22 ,, hydrogen, and 
7-11 „ oxygen. 

Empirical and rational formula*. — In order to deduce from these num- 
bers the chemical Jormula for oxalic acid, that is, the formula expressing 
the number of atoms of each element, it will be necessary, of course, to 
divide the weight of each element by the number representing its atomic 
weight. 

Thus 2*67 -7- 12 = 0'22 atomic proportion of carbon; 
0-22 -f- 1 = 0-22 „ „■ hydrogen; 

7*11 -T- 16 = 0-44 „ „ oxygen. 

Dividing these numbers by 0*22, the formula of oxalic acid might be 
written CH0 2 . This, however, is only an empirical formula for oxalic 
acid, that is, a formula which represents its composition only, without 
reference to its constitution, i.e., to the absolute number of atoms pre- 
sent, and to the mode in which they are grouped or arranged within the 
compound. A formula professing to give such information would be 
termed a rational formula, and can only be arrived at by the careful study 
of the relation of the substance under examination to others of which the 
combining weights are certainly known. Thus, it is found that one 
molecule (56 parts) of caustic potash (KHO) requires 45 parts of dry 
oxalic acid to neutralise it and form the potassium oxalate. Hence it is 
reasonable to regard 45 as the molecular weight of dry oxalic acid. This 
is the quantity which would be expressed by the formula CH0 9 . The 
action of oxalic acid upon caustic potash would then be represented 
by the equation KHO -I- CH0 2 == H 2 + CK0 2 (potassium oxalate). But 
there is another oxalate which has the formula C 2 KH0 4 (hydropotassic 



86 



SALTS FORMED BY CARBONIC ACID. 



oxalate) in which only one half of the hydrogen is displaced by potassium. 
Hence there must be 2 atoms of hydrogen in the molecule of oxalic acid, 
and its formula is C 9 H 4 . In determining whether this formula 
represents only one grouping of the elements, or whether it contains two 
or more groups in combination, the chemist is guided by the results of a 
more minute study of the decompositions which the compound undergoes 
under varied conditions. 



62. Salts formed by carbonic acid. — Although so ready to combine with 
the alkalies and alkaline earths (as shown in its absorption by solution 
of potash and by lime-water), carbonic acid must be classed among the 
weaker acids. It does not neutralise the alkalies completely, and it may be 
displaced from its salts by most other acids. Its action upon the colouring- 
matter of litmus is feeble and transient. If a solution of carbonic acid be 
added to blue infusion of litmus, a wine-red liquid is produced, which 
becomes blue again when boiled, losing its carbonic acid : whilst litmus 
reddened by sulphuric, hydrochloric, or nitric acid, acquires a brighter 
red colour, which is permanent on boiling. 

With each of the alkalies carbonic acid forms two well-defined salts, 
the carbonate and bicarbonate. Thus, the carbonates of potassium and 
sodium are represented by the formulae, K 2 C0 3 and Na 2 C0 3 , whilst the 
bicarbonates are KHC0 3 and NaHC0 3 . The existence of the latter salts 
would favour the belief in the existence of the compound H 2 C0 3 , although 
no such combination has yet been obtained in the separate state. Perfectly 
dry carbonic acid gas is not absorbed by pure quicklime (CaO), but 
when a little water is added, combination at once takes place. This 
supports the view entertained by some chemists, that C0 2 is not an acid 
until it is associated with water, and they therefore speak of it as 
carbonic anhydride, reserving the name carbonic acid for the as yet 
undiscovered compound H 2 O.C0 2 (or H 2 C0 3 ). 

Opposed to this view, however, is the fact that quicklime will absorb 
carbonic acid gas when heated to a certain point. 

Two hard glass tubes closed at one end, and bent as 
in fig. 84, are perfectly dried, and filled, over mercury, 
with well-dried carbonic acid gas. Fragments of lime 
are taken, whilst red hot, out of a crucible, cooled under 
the mercury, inserted into the tubes, and transferred 
to the upper end. ISTo absorption of the gas takes place, 
though the tubes be left for some days ; but if one of 
them be heated by a Bunsen burner, the absorption of 
carbonic acid gas takes place rapidly, and the mercury 
is forced up into the tube. 

The carbonates may be expressed either by additive 
formulae, showing the bases which combine with car- 
bonic acid to produce them, or by substitutive formulae, 
in which they are represented as formed from the 
hypothetical H 2 C0 3 by the substitution of metals for the 
hydrogen. In the latter formulae the existence of C0 2 
is lost sight of altogether. 

The formula H 2 C0 3 represents carbonic acid as a 
dibasic acid, that is, an acid containing two atoms of 
hydrogen which may be replaced by metals. 
Carbonates may be normal, acid, or basic. A normal carbonate is one in which all 
the hydrogen in H. 2 C0 3 is replaced by a metal or metals. 

An acid carbonate is one in which only half of the_ hydrogen is replaced by a metal. 
A basic carbonate is a normal carbonate in combination with a hydrate of the metal. 




Fig. 84. 



CARBONATES. 



87 



The following are some of the principal carbonates which are found in 
nature or employed in the arts : — 



Chemical Name. 


Common Name. 


Additive Formula. 


Substitutive Formula. 


Potassium car- 
bonate. 


[ Potashes, Pearl-a. 


sh. 


K 2 0.C0. 2 


K 2 C0 3 


: Hydropotassie 
carbonate. 
Sodium carbon- 
ate. 


^ Bicarbonate of 
) potash. 
\ Alkali. j 
) Washing soda. ) 


K. 2 O.H 2 0.2C0 2 

Na. 2 0.H 2 0.2C0. 2 

• 


KHC0 3 

Na 2 HC0 3 


Hydrosodic car- 
bonate. 


| Bicarbonate of soda. 


Na 2 O.H 2 0.2C0 2 


NaHC0 3 


Ammonium ses- 
quicarbonate. 


( Smelling salts. 

) Preston salts. 

J Carbonate of am 


1 
i 
1 


4NH 3 .3H 2 0.3C0 2 


(NH 4 ) 4 H,(C0 3 ) 3 


Calcium carbon- 
ate. 

Basic magnesium 
carbonate. 


( monia. 

\ Limestone, chalk. 

\ Marble. 

{ Magnesia alba. 

\ Magnesia. 


CaO.C0 2 

5(MgO.C0 2 ) I 
2(MgO.H 2 0) | 


CaC0 3 
5MgC0 3 .2Mg(HO) 2 


Ferrous carbon- 
ate. 


| Spathic iron ore. 




FeO.CO, 


FeC0 3 


Zinc carbonate. 
Basic copper car- 
bonate. 
Basic lead car- 
bonate. 
Carbonate of cal- 
cium and mag- 
nesium. 

1 


Calamine. 
[ Malachite. 

( White lead. 

( Dolomite. 

< Magnesian lime- 

( stone. 


I 

1 
I 


ZnO.C0 2 
CuO.CO, ) 
CuO.H 2 6 \ 
■2(PbO.C0 8 ) 
PbO.H 2 \ 

CaO.Mg0.2C0 2 


ZnC0 3 

CuC0 3 .Cu(HO) 2 

2PbC0 3 .Pb(HO) 2 
MgCa2C0 3 



63. Analytical proof of the composition of carbonic acid gas. — Lavoisier appears to 
have been the first to prove that carbonic acid gas was formed when carbon combined 
with oxygen, but its composition was first analytically demonstrated by Smithsou 
Tennant, who heated carbonate of lime with phosphorus in a sealed glass tube, and 
obtained phosphate of lime and carbon, the latter having parted with its oxygen to 
convert the phosphorus into phosphoric acid. 




Fig. 85. 

A far easier method of demonstrating the composition of carbonic acid gas consists 
in introducing a pellet of potassium into a bulb tube, through which a current of car- 
bonic acid gas (dried by passing through oil of vitriol, or over chloride of calcium) is 
flowing, and applying the heat of a spirit-lamp to the bulb. The metal will soon 
burn in the gas, which it robs of its oxygen, leaving the carbon as a black mass in 
the bulb (fig. 85). The potash produced by the oxidation of the potassium enters 



88 



CARBONIC OXIDE IN FIRES AND FURNACES. 



into combination with another portion of the carbonic acid gas, forming a "white mass 
of potassium carbonate, 3C0 2 + K 4 = 2K 2 C0 3 + C. If slices of sodium be arranged in 
a test-tube in alternate layers with dried chalk (calcium carbonate), and strongly- 
heated with a spirit-lamp, vivid combustion will ensue, and much carbon will be 
separated (CaC0 3 + Na 4 = CaO + 2Na. 2 + C). 

When the action of the sodium upon carbonic acid gas is moderated by employing 
it in the form of a mixture with pure dry sand, and by keeping the temperature below 
the boiling point of mercury, sodium oxalate is produced by the combination of 



the sodium with the elements of the carbon dioxide 
oxalate). 



Na 2 + 2C0 2 = Na 2 C 2 4 (sodium 



64. Carbonic oxide (CO = 28 parts by weight = 2 volumes). — Other 
metals, which are not endowed with so powerful an attraction for oxygen, 
do not carry the decomposition of carbon dioxide to its final limit; thus, 
iron and zinc* at a high temperature will only deprive the gas of one half 
of its oxygen, a result which may also be brought about at a red heat by 
carbon itself. If an iron tube filled with fragments of charcoal be heated 
to redness in a furnace (fig. 9), and carbonic acid gas be transmitted 
through it, it will be found, on collecting the gas which issues from the 
other extremity of the tube, that it has no longer the properties of carbonic 
acid, but that, on the approach of a taper, it takes lire, and burns with a 
beautiful blue lambent flame, similar to that which is often observed to 
play over the surface of a clear fire. Both flames, in fact, are due to the 
same gas, and in both cases this gas results from the same chemical 
change, for, in the tube, the carbonic acid gas yields half of its oxygen to 
the char)oal, both becoming converted into carbonic oxide ; C0 2 + C = 
2 CO. In the fire the carbonic acid gas is formed by the combustion of 
the carbon of the fuel in the oxygen of the air entering at the bottom of 
the grate; and this carbonic acid gas in passing over the layer of heated 
carbon in the upper part of the fire, is partly converted into carbonic oxide, 
which inflames when it meets with the oxygen in the air above the surface 
of the fuel, and burns with its characteristic blue flame, reproducing 
carbon dioxide. The carbonic oxide occupies twice the volume of the 
carbon dioxide from which it was produced. 

This conversion of carbon dioxide into carbonic oxide is of great import- 




mmM?' 

Fig. 86. — Reverberatory furnace for copper smelting. 

ance on account of its extensive application in metallurgic operations. It 
is often desirable, for instance, that a flame should be made to play over 
the surface of an ore placed on the bed or hearth of a reverberatory fur- 
nace (fig. 86). This object is easily attained when the coal affords a large 
quantity of inflammable gas ; but with anthracite coal, which burns with 



Magnesium also reduces carbon dioxide to carbonic oxide. 



PROPERTIES OF CARBONIC OXIDE. 89 

very little flame, and is frequently employed in such furnaces, it is neces- 
sary to pile a high column of coal upon the grate, so that the carbon 
dioxide formed beneath may be converted into carbonic oxide in passing- 
over the heated coal above, and when this gas reaches the hearth of the 
furnace, into which air is admitted, it burns with a flame which spreads 
over the surface of the ore. The temperature of the flame of carbonic 
oxide burning in air is estimated at about 2050° C. 

The attraction of carbonic oxide for oxygen is turned to account in 
removing that element from combination with iron in its ores, as will be 
seen hereafter. 

Carbonic oxide is a gas of so poisonous a character that, according to 
Leblanc, 1 volume of it diffused through 100 volumes of air totally 
unfits it to sustain life ; and it appears that the lamentable accidents 
which too frequently occur from burning charcoal or coke in braziers and 
chafing-dishes in close rooms, result from the poisonous effects of the 
small quantity of carbonic oxide which is produced and escapes conibus 
tion, since the amount of carbonic acid gas thus diffused through the air 
is not sufficient, in many cases, to account for the fatal result. The 
carbonic oxide formed in cast-iron stoves diffuses through the hot metal 
into the air of a room. 

65. The knowledge of the poisonous character of carbonic oxide gave 
rise a few years since to considerable apprehension, when it was proposed 
to employ this gas in Paris for purposes of illumination. The character 
of the flame of carbonic oxide would appear to afford little promise of its 
utility as an illuminating agent; but that it is possible so to employ it is 
easily demonstrated by kindling a jet of the gas which has been passed 
through a wide tube containing a little cotton moistened with rectified 
coal naphtha (benzene), when it will be found to burn with a very luminous 
flame. The carbonic oxide destined to be employed for illuminating pur- 
poses was prepared by passing steam over red hot coke or charcoal, when 
a highly inflammable gas was obtained, containing carbon dioxide, carbonic 
oxide and hydrogen ; 4H 2 + C 3 = C0 2 + 2CO + H 8 . 

Since neither hydrogen nor carbonic oxide burns with a luminous flame, 
this gas was next passed into a vessel containing red hot coke, over which 
melted resin was allowed to trickle. The action of heat upon the resin 
gave rise to the production of vapours similar to that of the benzene em- 
ployed in the above experiment, and which, in like manner, conferred 
considerable illuminating power upon the gas. 

The decomposition of steam by red hot carbon is also taken advantage 
of in order to procure a flame from anthracite coal when employed for 
heating boilers. The coal being burnt on jish-bettied bars, beneath which 
a quantity of water is placed, the radiated heat converts the water into 
steam, which is carried by the draught into the fire, where it furnishes 
carbonic oxide and hydrogen, both capable of burning with flame under 
the bottom of the boiler. The temperature of the bars is also thus re- 
duced, so that they are not so much injured by the intense heat of the 
glowing fuel. 

66. Carbonic cxide, unlike carbon dioxide, is nearly insoluble in water. 
It is even lighter than air, its specific gravity being 0'967. In its 
chemical relations it is an indifferent oxide, that is, it has neither acid nor 
basic properties. It has been liquefied by the cold produced by its own 
expansion under a compression of 300 atmospheres at - 29° C. 



90 



PREPARATION OF CARBONIC OXIDE. 



67. A very instructive process for obtaining carbonic oxide, consists in heating 
crystallised oxalic acid with three times its weight of oil of vitriol. If the gas be 
collected over water (fig. 87), and one of the jars be shaken with a little lime-water, 
the milkiness imparted to the latter will indicate abundance of carbon dioxide ; 

whilst, on removing the glass 
plate, and applying a light, 
the carbonic oxide will burn 
with its charactistic blue flame. 
The gas thus obtained is a 
mixture of equal volumes of 
carbonic oxide and carbonic acid 
gases. Crystallised oxalic acid 
is represented by the formula 
C 2 H 2 4 .2Aq., and if the water 
of crystallisation be left out of 
consideration, its decomposition 
may be represented by the equa- 
tion — 

C 2 H 2 4 

the chari£ 

the attraction of the oil of vitriol 
for water. To obtain pure car- 
bonic oxide, the mixture of gases must be passed through a bottle containing solution 
of potash, to absorb the carbonic acid gas (fig. 88). 

But pure carbonic oxide is much more easily obtained by the action of sulphuric 
acid upon crystallised potassium ferrocyanide (yellow prussiate of potash) at a 




Fig. 8; 



H 2 + CO + C0 2 , 
being determined by 







;7^- 



Fig. 88. — Preparation of carbonic oxide. 

moderate heat. Since the gas contains small quantities of sulphurous and carbonic 
acid gases, it must be passed through solution of potash if it be required perfectly 
pure. The chemical change which occurs in this process is expressed thus : — 

K 4 C 6 N fi Fe + 6H 2 + 6H. 2 S0 4 = 6CO + 2K,S0 4 + 3(NH 4 ) 2 S0 4 + FeS0 4 
Potassinm Potassium Ammonium Ferrous 

ferrocyanide. sulphate. sulphate. sulphate. 

Ten grammes of crystallised ferrocyanide, with 135 grammes of sulphuric acid 
(sp. gr. 1*84) and 13 grammes of waiter, will give about 3^ litres of carbonic oxide. 

If the boiling is continued after the evolution of CO has ceased, much sulphurous 
acid gas is disengaged (2FeS0 4 + 2H 2 S0 4 = Fe 2 (S0 4 ) 3 + 2H 2 + S0 2 ). 

68. To demonstrate the production of carbonic acid gas during the combustion of 
carbonic oxide, a jar of the gas is closed with a glass plate, and after placing it upon 



CAKBONIC OXIDE. 



91 



the table, the plate is slipped aside and a little lime-water quickly poured into the 
jar. On shaking, no milkiness indicative of carbonic acid gas should be perceived. 
The plate is then removed and the gas kindled. On replacing the plate and shaking 
the jar, an abundant precipitation of calcium carbonate will take place. 

When carbonic oxide is passed through a red hot porcelain tube, a portion of it is 
decomposed into carbonic acid gas and carbon ; and when the experiment is conducted 
Avithout special arrangements, the carbonic oxide is reproduced as the temperature of 
the gas falls. But by passing through the centre of the porcelain tube a brass tube, 
through which cold water is kept running, the decomposition has been demonstrated 
by the deposition of carbon upon the cooled tube, and by collecting the carbonic acid 
gas formed. 

Carbonic acid gas is also decomposed by intense heat into carbonic oxide and 
oxygen ; but if these gases be allowed to cool down slowly in contact, they recombine. 
The gas drawn from the hottest region of a blast-furnace (see Iron), and rapidly 
cooled, so as to prevent recombination, was found to contain both carbonic oxide and 
oxygen. 

According to Brodie, carbonic acid gas is partially decomposed into carbonic oxide 
and oxygen by electric inductive discharge (p. 54), and § of the oxygen assumes the 
form of ozone. 

By passing a pellet of phosphorus up into carbonic acid gas, over mercury, in a 
eudiometer, and passing electric sparks for some days, the gas has been entirely 
decomposed, an equal volume of carbonic oxide being left. 

The reducing action of carbonic oxide upon metallic oxides, at high temperatures, 




Fig. 89. — Reduction of oxide of copper by carbonic oxide. 

may be illustrated by passing the pure gas from a bag or gas-holder, first through 
bottle of lime-water (B, fig. 89), to prove the absence of carbonic acid gas, then over 
oxide of copper, contained in the tube 0, and afterwards again through lime-water 
in D. When enough gas had been passed to expel the air, heat may be applied to 
the tube by the gauze-burner E, when the formation of carbonic acid gas will be im- 
mediately shown by the second portion of lime-water, and the black oxide of copper 
will be reduced to red metallic copper. 

If precipitated psroxide of iron be substituted for oxide of copper, iron in the state 
of black powder will be left, and if allowed to cool in the stream of gas, will take fire 
when it is shaken out into the air, becoming reconverted into the peroxide {iron 
pyropl torus). 

69. Composition by volume oj carbonic oxide and carbon dioxide. — 
When carbon burns in oxygen, the volume of the carbon dioxide produced 
is exactly equal to that of the oxygen, so that one volume of oxygen fur- 
nishes one volume of carbonic acid gas, or a molecule (two volumes, see 
p. 2) of carbonic acid gas contains two volumes of oxygen. 

When one volume of carbonic acid gas (containing one volume of 
oxygen) is passed over heated carbon, it yields two volumes of carbonic 
oxide ; hence two volumes, or one molecule, of this gas contain one 
volume of oxygen. 



Specific gravity (to H) of C0 2 , i.e., weight of one volume, 
Specific gravity (to H) or weight of one volume, of 0, 

Weight of carbon in one volume of C0 2 , 



ACETYLENE. 



Hence, a molecule, two volumes or 44 parts by weight, of C0 2 , contains 12 parts 
by weight of carbon. 



Specific gravity (to H), or weight of one volume, of CO, 
"Weight of two volumes of CO, .... 
,, one volume of 0, .... 



14 



12 



"Weight of carbon in two volumes (or one molecule) of CO, 

70. The atomic 'weight of carbon is taken as 12, since this is the 
smallest weight of carbon which can be found in two volumes of any of 
its gaseous compounds. 



Compounds of Carbon and Htdeogen. 

71. ISTo two other elements are capable of occurring in so many different 
forms of combination as carbon and hydrogen. The hydrocarbons, as 
their compounds are generally designated, include most of the inflammable 
gases which are commonly met with, and a great number of the essential 
oils, naphthas, and other useful substances. There is reason to believe 
that all these bodies, even such as are found in the mineral kingdom, 
have been originally derived from vegetable sources, and their history 
belongs, therefore, to the department of organic chemistry. The three 
simplest examples of such compounds will, however, be brought forward 
in this place to afford a general insight into the mutual relations of these 
two important elements. Their names and composition are — 





Formulas. 
(2 volumes.) 


Parts by Weight. 


Acetylene, 
Marsh gas, 
Olefiant gas, . 


C 2 H. 2 
CH 4 
C. 2 H 4 


c 

24 
12 
24 


H 

2 

4 

4 



72. Acetylene* — When very intensely heated, carbon is capable of 
combining with hydrogen to form acetylene. The required temperature 
is procured by means of a powerful galvanic battery, to the terminal wires 
of which two pieces of dense carbon are attached, and the voltaic discharge 
is allowed to take place between them in an atmosphere of hydrogen. 
The experiment possesses little practical importance, because but little 
acetylene is formed in proportion to the force employed, but its theoretical 
interest is very great, since it is the first step in the production of organic 
substances by the direct synthesis of mineral elements ; acetylene (C 9 H 2 ) 
being convertible into olefiant gas (C 2 H 4 ), this last into alcohol (C 2 H 6 0), 
and alcohol into a very large number of organic products. 

Acetylene is constantly found among the products of the incomplete 
combustion and destructive distillation of substances rich in carbon ; 
hence it is always present in small quantity in coal gas, and may be pro- 
duced in abundance by passing the vapour of ether through a red hot 
tube. The character by whieh acetylene is most easily recognised is that 

* Long known as klumene, having been obtained in 1836 by the action of water upon a 
compound containing carbon and potassium, produced during the preparation of that 
metal. The name acetylene is derived from the hypothetical radial acetyle (C 2 H 3 ), to 
which acetylene bears the same relation as ethylene (C 2 H 4 ) does to ethyle (C 2 H 5 ). 



PREPARATION OF ACETYLENE. 



93 



of producing a fine red precipitate in an ammoniacal solution of cuprous 
chloride (subchloride of copper). 

The most convenient process for preparing a quantity of this precipitate, is that 
in which the acetylene is produced by the imperfect combustion taking place when 
a jet of atmospheric air is allowed to burn in coal gas. 

An adapter (A, fig. 90), is connected at its narrow end with the pipe supplying 
coal gas. The wider opening is closed by 
a bung with two holes, one of which 
receives a piece of brass tube (B) about 
three-quarters of an inch wide and 7 inches 
long, and in the other is inserted a glass 
tube (C) which conducts the gas to the 
bottom of a separating funnel (D). The 
lower opening of the brass tube B is closed 
with a cork, through which passes the 
glass-tube E connected with a gas-holder 
or bag containing atmospheric air. To 
commence the operation, the gas is turned 
on through the tube F, and when all air 
is supposed to be expelled, the tube E is 
withdrawn, together with its cork, and a 
light is applied to the lower opening of 
the brass tube, the supply of coal gas 
being S3 regulated that it shall burn with 
a small flame at the end of the tube. A 
feeble current of air is then allowed to 
issue from the tube E, which is passed up 
through the flame into the adapter, where 
the jet of air continues to burn in the. 
coal gas,* and may be kept burning for 
hours with a little attention to the pro- 
portions in which the gas and air are 
supplied. A solution of cuprous chloride 
in ammonia is poured into the separating 
funnel through the lateral opening G-, so 
that the imperfectly burnt gas may pass 
through it, when the cuprous acetylide 
is precipitated in abundance. When a sufficient quantity has been formed, or the 
copper solution is exhausted, the liquid is run out through the stopcock (H) on to a 
filter, and replaced by a fresh portion. The precipitate may be rinsed into a flask 
provided with a funnel tube and delivery tube, allowed to subside, the water decanted 
from it, and some strong hydrochloric acid poured in through the funnel. On heating, 
the acetylene is evolved, and may be collected, either over water, or more economically 
in a small gas-bag, or in a mercurial gas-holder. To obtain a pint of the gas, as 
much of the moist copper precipitate is required as will measure about 6 ounces after 
settling down. Such a quantity may be prepared in about six hours. 

A solution of cuprous chloride suitable for this experiment is conveniently pre- 
pared in the following manner: — 500 grains of black oxide of copper are dissolved 
in 7 measured ounces of common hydrochloric acid, in a flask, and boiled for 
about twenty minutes with 400 grains of copper in filings or fine turnings. The 
brown solution of cuprous chloride in hydrochloric acid, thus obtained, is poured into 
about 3 pints of water contained in a bottle ; the white precipitate (cuprous 
chloride) is allowed to subside, the water drawn off with a siphon, and the precipitate 
rinsed into a 20-ounce bottle, which is then quite filled with water and closed 
with a stopper. When the precipitate has again subsided, the water is drawn off, 
and 4 ounces of powdered chloride of ammonium are introduced, the bottle being 
again filled up with water, closed and shaken. The cuprous chloride is entirely 
dissolved by the chloride of ammonium, but would be precipitated if more water 
were added. When required, for the precipitation of acetylene, the solution may be 
mixed with about one-tenth of its bulk of strong ammonia ("880), which may be 
poured into the separating funnel (D) before the copper solution is introduced. 

* It is advisable to attach a piece of thin platinum wire to the mouth of the glass tube 
to render the flame of the air more visible. 




Fig. 90. — Preparation of cuprous acetylide. 



94 PROPERTIES OF ACETYLENE. 

Four measured ounces of the solution are sufficient for one charge, and yield, in 
three hours, about 3 measured ounces of the moist precipitate. The blue solution 
of ammoniacal cupric chloride, filtered from the red precipitate, may be rendered 
serviceable again by being shaken, in a stoppered bottle, with precipitated copper, 
prepared by reducing a solution of sulphate of copper, acidulated with hydrochloric 
acid, with a plate of zinc. 

The red precipitate is called cupros-ethenyle hydrate, and its formation 
is explained by the equations (1) C 2 H 2 + Cu 2 Cl 2 + NH 3 = C 2 HCu 2 Cl 
+ NH 4 C1 ; (2) C 2 HCu 2 Cl + M 3 + H 2 = C 2 HCu 2 OH + NH 4 C1. 

If the acetylene copper precipitate be collected on a filter, washed, and 
dried either by mere exposure to the air, or over oil of vitriol, it will be 
found to explode with some violence when gently heated, and it is said 
that the accidental formation of this compound in copper or brass pipes, 
through which coal gas passes, has occasionally given rise to explosions. 

When acetylene is passed through solution of nitrate of silver, a white curdy pre- 
cipitate is formed, resembling chloride of silver in appearance, but insoluble in 
ammonia (which turns it yellow) as well as in nitric acid. It may be obtained by 
allowing the imperfectly burnt gas from the apparatus in fig. 90 to pass through 
nitrate of silver. 

It may be more easily prepared by suspending a funnel over aBunsen burner which 
has caught fire inside the tube, and drawing the products of imperfect combustion, by 
means of an aspirator, through a solution of silver nitrate. This precipitate may 
also be used for the preparation of acetylene, by heating it with hydrochloric acid. 

When this precipitate is washed and allowed to dry, it is violently explosive if 
heated or struck.* A minute fragment of it placed on a glass plate, and touched 
with a red hot wire, detonates loudly and shatters the glass like fulminate of silver. 
The explosive silver compound is the argent-cihenyle hydrate, C 2 HAg. 2 OH, the chloride 
corresponding to it (C. 2 HAg 2 Cl) being precipitated when acetylene is passed through 
a solution of chloride of silver in ammonia. In a solution of hyposulphite of gold 
and sodium, acetylene gives a yellowish very explosive precipitate. 

When potassium or sodium is heated in excess of acetylene, it is said that one- 
half of the hydrogen is displaced by the metal, forming acetylide of potassium 
(C. 2 HK) or of sodium (C 2 HNa), a portion of the acetylene being converted into olefiant 
gas (C. 2 H 4 ) by combination with the displaced hydrogen. When heated to dull red- 
ness, sodium completely decomposes acetylene, C 2 Na 2 being obtained. Both these 
sodium compounds are violently decomposed by water, acetylene being reproduced. 

The copious formation of acetylene during the imperfect combustion of ether, is 
very readily shown by introducing a few drops of ether into a test-tube, adding a 
little ammoniacal solution of cuprous chloride, kindling the ether-vapour at the 
mouth of the tube, and inclining the latter so as to expose a large surface of the 
copper solution, when a large quantity of the red cuprous acetylide is produced. If 
nitrate of silver be substituted for the copper solution, the white precipitate of oxide 
of argent-ethenyle is formed abundantly. 

Acetylene has been found accompanying the vapour of hydrocyanate of ammonia 
produced by the action of ammonia on red hot charcoal. 

It has also been prepared by distilling ethene dibromide with alcoholic solution of 
potash; C. 2 H 4 Br 2 + 2KHO = C 2 H 2 + 2KBr + 2H 2 ; and by the action of sodium on 
chloroform ; 2CHC1 3 + Na 6 = 6NaCl + C 2 H 2 . 

Acetylene is a colourless gas having a peculiar odour, recalling that of 
the geranium, which is always perceived where coal gas is undergoing 
imperfect combustion. It burns with a very bright smoky flame. Its 
most remarkable property is that of inflaming spontaneously when brought 
in contact with chlorine. If a jet of the gas be allowed to pass into a 
bottle of chlorine, it will take fire and burn with a red flame, depositing 
much carbon. When chlorine is decanted up into a cylinder containing 
acetylene standing over water, a violent explosion immediately takes 

* If the precipitate is prepared from a slightly ammoniacal solution of nitrate of silver, 
it is more sensitive to a blow. 



OLEFIANT GAS. 



95 



place, attended with a vivid flash, and separation of a large amount of 
carbon ; C 2 H 2 + Cl 2 = C 2 + 2HC1 . 

When acetylene is passed into water, it is absorbed in sufficient quan- 
tity to impart a strong smell to the water, and to yield a decided precipi- 
tate with ammoniacal cuprous chloride and with silver nitrate. 

The action of heat upon acetylene is very remarkable and instructive, 
since it results in the formation of a complex body from one which is less 
complex in composition. When heated in a glass tube for half an hour 
to the point at which the glass began to soften, it was found to be reduced 
to one-fifth of its original volume, the greater portion of it having been 
converted into a liquid hydrocarbon, ethenyle - benzene or styrolene, 
C,.H 5 .C 2 H 3 , hitherto obtained from the vegetable gum-resin known as 
storax. The remaining gas was chiefly hydrogen (a little carbon having 
separated) with a little defiant gas. Benzene (C 6 H 6 ) has been formed, in 
a similar way, from three molecules of acetylene. When heated in contact 
with coke or iron, the bulk of the acetylene is decomposed into its 
elements. 

By suspending the acetylene copper precipitate in solution of ammonia, 
and heating with a little granulated zinc, Berth elot has induced the 
acetylene to combine Avith the {nascent) hydrogen to form defiant gas 

( C 2 H 4 )- 

When a mixture of acetylene with nitrogen is acted on by a succession 
of electric sparks, hydrocyanic or prussic acid (HCN) is produced by their 
direct union. 

73. Olefiant gas or ethylene (C 2 H 4 = 28 parts by weight ~2 volumes). — 
This gas is found in larger quantity than acetylene, among the products 
of the action of heat upon coal 

and other substances rich in f^X Flff 

carbon, and it is one of the most 
important constituents of the 
illuminating gases obtained from 
such materials. 

Olefiant gas may readily be 
prepared by the action of strong 
sulphuric acid (oil of vitriol, 
H 2 S0 4 ) upon alcohol (spirit of 
wine, C 2 H 6 0). 

' Two measures of oil of vitriol are 
introduced into a flask (fig. 91), and 
one measure of alcohol is gradually 
poured in, the flask being agitated 
after each addition of the acid ; much 
heat is evolved, and there would be danger in mixing large volumes suddenly.* On 
applying a moderate heat, the liquid will darken in colour, effervescence will take 
place, and the gas may be collected in jars filled with water. When the mixture has 
become thick, and the evolution of the gas is slow, the end of the tube must be 
removed from the water and the lamp extinguished. Three measured ounces of spirit 
of wine generally give about 500 cubic inches of olefiant gas. 

The gas will be found to have a very peculiar odour, in which that of ether and of 
sulphurous acid gas are perceptible. One of the jars may be closed with a glass plate, 
and placed upon the table with its mouth upwards ; on the approach of a flame, the 
gas will take fire, burning with a bright white flame characteristic of olefiant gas, and 




Fig. 91. — Preparation of olefiant gas 



If methylated spirit be employed, the mixture will have a dark red-brown colour. 



96 



OLEFIANT GAS. 




Fig. 92. 



seen to best advantage when, after kindling the gas, a stream of water is poured 
down into the jar in order to displace the gas (fig. 92). 

Another jar of the gas may be well washed by 
transferring it repeatedly from one jar to another 
under water, a little solution of potash may then be 
poured into it, and the jar violently shaken, its 
mouth being covered with a glass plate ; the potash 
will remove all the sulphurous acid gas, and the gas 
will now exhibit the peculiar faint odour which 
belongs to olefiant gas. 

The purified gas may be transferred, under water, 
to another jar, kindled and allowed to burn out; if 
a little lime-water be then shaken in the jar, its 
turbidity will indicate the presence of carbonic acid 
gas, which is produced together with water, when 
olefiant gas burns in air: C. 2 H 4 + 6 = 2C0. 2 + 2H 2 0. 

Ethylene has been liquefied by a pressure of 63 
atmospheres at 10° C. 

On comparing the composition of olefiant 
gas (C 2 H 4 ) with that of alcohol (C 2 H 6 0), it is 
evident that the former may be supposed to 
be produced from the latter by the abstraction 
of a molecule of water (H 2 0) which is removed 
by the sulphuric acid, though other secondary 
changes take place, resulting in the separation 
of carbonaceous matter and the production of 
sulphurous acid gas. A more complete explanation of the action of 
sulphuric acid upon alcohol must be reserved for the chemical history of 
this compound. 

Olefiant gas derives its name from its 
property of uniting with chlorine and 
bromine to form oily liquids, a circum- 
stance which is applied for the determina- 
tion of the proportion of this gas present 
in coal gas, upon which great part of the 
illuminating value of coal gas depends. 
The compound with chlorine (C 2 H 4 C1 2 ) is 
known as Dutch liquid, having being- 
discovered by Dutch chemists, and is 
remarkable for its resemblance to chloro- 
form in odour. 

When ethene-dibromide (C 2 H 4 Br. 2 ) is 
heated with an alcoholic solution of pot- 
ash, it yields acetylene. 

To exhibit the formation of Dutch liquid, a 

quart cylinder (fig. 93) is half filled with olefiant 

gas, and half with chlorine, which is rapidly 

passed up into it, from a bottle of the gas, under 

water. The cylinder is then closed with a glass 

plate, and supported with its mouth downwards 

under water in a separating funnel furnished 

with a glass stopcock. The volume of the mixed 

gases begins to diminish immediately, drops of 

^S- 93 - oil being formed upon the side of the cylinder 

and the surface of the water. As the drops increase, they fall to the bottom of the 

funnel. Water must be poured into the funnel to replace that which rises into the 

cylinder, and when the whole of the gas has disappeared, the oil may be drawn out of 




OLEFIANT GAS. 



97 




the funnel through the stopcock into a test-glass, in which it is shaken with a little 
potash to absorb any excess of chlorine. The fragrant odour of the Dutch liquid will 
then be perceived, especially on pouring it out into a shallow dish. 

In applying this principle to the measurement of the illuminating 
hydrocarbons in coal gas, daylight must be excluded, or an error 
would be caused by the union of the free hydrogen with the chlorine 
or bromine. The bromine test may be applied in the tube repre- 
sented in fig. 94. The gas to be examined is measured over water 
in the divided limb a, with due attention to temperature and 
pressure ; the tube being held perpendicularly, the limb b will remain 
filled with water, so that gas cannot escape nor air enter. A drop 
or two of bromine is poured into this limb, which is then depressed 
beneath the water in the pneumatic trough, and closed by the 
stopper c. On shaking the gas with the water and bromine, the 
latter will absorb the illuminating hydrocarbons; and if the tube 
be again opened under water, the volume of the gas in a will be found 
to have diminished, and the diminution gives an approximate esti- 
mate of the defiant gas and other illuminating hydrocarbons. 

A very instructive experiment consists in filling a three-pint 
cylinder one-third full of defiant gas, then rapidly filling it up, 
under water, with two pints of chlorine, closing its mouth with a 
glass plate, shaking it to mix the gases, slipping the plate aside and 
applying a light, when the mixture burns with a red flame which 
passes gradually down the cylinder, and is due to the combination of 
the hydrogen with the chlorine, the whole of the carhon being 
separated in the solid state — 

C 2 H 4 + C1 4 = 4HC1 + C 2 . 

When olefiant gas is subjected to the action of high temperatures, as 
by passing through heated tubes, one portion is decomposed into marsh 
gas (CH 4 ) with separation of carbon, whilst another portion yields 
acetylene (C 2 H 2 ) and hydrogen ; these decompositions w r ill be found to 
be of great importance in the manufacture of coal gas. 

The action of heat upon olefiant gas is most conveniently shown by exposing it to 
the spark from an induction-coil. 

The gas is confined in a tube (A, fig. 95) which is placed in a cylindrical jar (B) 
containing mercury. Through the mercury passes a copper 
wire (C) thrust through a glass tube (D) to insulate it from 
the mercury ; this wire is connected with one of the wires 
(E) from the induction-coil, whilst the other (F) is allowed 
to dip into the mercury contained in the cylinder. On 
putting the coil in action (with two or three cells of Grove's 
battery), the spark will pass between the extremity (C) of the 
insulated copper wire and the surface of the mercury in the 
tube, decomposing the olefiant gas in its passage, and causing 
a separation of carbon, which sometimes forms a conducting 
communication, and allows the current to pass without a 
spark. This may be obviated by reversing the current, or 
by gently shaking the tube. 

The olefiant gas will expand to nearly twice its former 
volume, so that the tube will gradually rise in the mercury, 
but the same distance may always be maintained for the 
passage of the spark. 

To show the production of acetylene, another arrangement 
will be found convenient (fig. 96). A globe with four necks 
is employed; through two of these necks are passed, air- 
tight with perforated corks, the copper wires connected with the induction-coil. A 
third neck receives a tube, conveying olefiant gas from a gas-holder, whilst from the 
fourth proceeds a tube dipping to the bottom of a small cylinder. When the whole 
of the air has been displaced by olefiant gas, a solution of cuprous chloride in ammonia 
is poured into the cylinder, and the gas allowed to bubble through it, when the 
absence of acetylene will be shown by there being no red compound formed. As soon, 
however, as the spark is passed, the red precipitate will appear, and, in a very few 

G 




PREPARATION OF MARSH GAS. 



minutes, a large quantity will be deposited. Coal gas may be employed instead of 
olefiant gas, but of course less of the copper compound will be obtained. 

74. Marsh gas or light carhuretted hydrogen (CH 4 = 16 parts by weight 
= 2 volumes). — This hydrocarbon is found in nature, being produced 

wherever vegetable matter 
is undergoing decomposition 
in the presence of moisture. 
The bubbles rising from 
stagnant pools, when col- 
lected and examined, are 
found to contain marsh gas 
mixed with carbonic acid 
gas, and there is reason to 
believe that these two 
gases represent the principal 
forms in which the hydro- 
gen and oxygen respectively 
were separated from wood 
during the process of its 
conversion into coal. This 
would account for the con- 
stant presence of this gas in 
the coal formations, where 
it is usually termed fire- 
damp. It is occasionally 
found pent up under pres- 
sure between the layers of 
coal, and the pores of the 
latter are sometimes so full 




Fig. 96. — Preparation of cuprous acetylide from 
olefiant gas. 



of it that it may be seen rising in bubbles when the freshly hewn coal is 
thrown into water. Perhaps a similar origin is to be ascribed to the liquid 
hydrocarbons chemically similar to marsh gas, which are found so abund- 
antly in Pennsylvania and Canada, and are known by the general name 
of petroleum. From certain gas-springs in Pennsylvania, marsh gas, 
olefiant gas, and ethyle hydride, C 2 H 6 , are discharged at very high pressure, 
and are employed for heating and lighting. 

Marsh gas is obtained artificially by the following process : — 

500 grains of dried sodium acetate are finely powdered and mixed in a mortar, with 
200 grains of solid potash, and 300 grains of powdered quicklime (or with 500 grains 
of the mixture of calcium hydrate and sodium hydrate, which is sold as soda-lime). 
The mixture is heated in a Florence flask (or better a copper tube, for the alkali cor- 
rodes the glass) and the gas collected over water (fig. 97). 

The decomposition will be evident from the following equation : — 

NaC 2 H 3 2 + NaHO = Na 2 C0 3 + CH 4 

Sodium acetate. Caustic soda. Sodium carbonate. 

The marsh gas will be easily recognised by its burning with a pale 
illuminating name, far inferior in brilliancy to those of olefiant gas and 
acetylene, but unattended with smoke. 

The properties of this gas deserve a careful study, on account of the 
frequent fatal explosions to which it gives rise in coal-mines, where it is 
often found accumulated under pressure, and discharging itself with con- 
siderable force from the fissures or blowers made in hewing the coal. 



PROPERTIES OF MARSH GAS. 



99 



Marsh gas has no characteristic smell like coal gas, and the miner thence 
receives no timely warning of its presence ; it is much lighter than air 
(sp. gr. 0*5596), and therefore very readily diffuses* itself (page 18) 




Fig, 97. — Preparation of marsh gas. 

through the air of the mine, with which it forms an explosive mixture as 
soon as it amounts to one-eighteenth of the volume of the air. The gas 
issuing from the blower would burn quietly on the application of a light, 
since the marsh gas is not explosive unless mixed with the air, when a 
large volume of the gas is burnt in an instant, causing a sudden evolution 
of a great deal of heat, and a consequent sudden expansion or explosion 
exerting great mechanical force. The most violent explosion takes place 
when 1 volume of marsh gas is mixed with 2 volumes of oxygen, since 
this quantity is exactly sufficient to effect the complete combustion of 
the carbon and hydrogen of the gas, and therefore to evolve the greatest 
amount of heat : CH 4 + 4 = C0 2 + 2H 2 0. The calculated pressure 
exerted by the exploding mixture of marsh gas and oxygen amounts to 
37 atmospheres, or 555 lbs. upon the square inch. Since air contains 
one-fifth of its volume of oxygen, it would be necessary to employ 10 
volumes of air to 1 volume of marsh gas in order to obtain perfect com- 
bustion, but the explosion will be much less violent on account of the 
presence of the 8 volumes of inert nitrogen, the calculated pressure 
exerted by the explosion being only 14 atmospheres, or 210 lbs. on the 
square inch. Of course, if more air is employed, the explosion will be 
proportionally weaker, until, when there are more than 18 volumes of 
air to each volume of marsh gas, the mixture will be no longer explosive, 
but will burn with a pale flame around a taper immersed in it. The car- 
bonic acid gas resulting from the explosion is called by miners the after- 
damp, and its effects are generally fatal to those who may have escaped 
death from the explosion itself. 

Fortunately, marsh gas requires a much higher temperature to inflame 
it than most other inflammable gases ; a solid body at an ordinary red 
heat does not kindle the gas unless kept in contact with it for a consider- 
able period ; contact with flame, or with a body heated to whiteness, 
being required to ignite it instantaneously. 

* AnselVs fire-clamp indicator is an apparatus in which the high rate of diffusion of 
marsh gas is taken advantage of in order to detect its presence in the air of mines. The 
apparatus represented in fig. 14 illustrates its principle. 



100 



EXPLOSION OF MARSH GAS WITH AIR. 




If two strong gas cylinders be filled, respectively, with mixtures of 2 volumes 
hydrogen with 1 volume oxygen, and of 1 volume marsh gas and 2 volumes oxygen, 
it will be found, on holding them with their mouths downwards, and inserting a red 

hot iron bar (fig. 98), that the marsh gas mixture 
will not explode, but if the bar be transferred at 
once to the hydrogen mixture, explosion will take 
place. A lighted taper may then be used to 
explode the marsh gas and oxygen. 

Coal gas, although answering very well for 
many illustrations of the properties of marsh 
gas, cannot be used in this experiment, since 
some of its constituents inflame at a far lower 
temperature. 

In consequence of the high temperature 
required to inflame the mixture of marsh 
gas and air, it is necessary that the mixture 
be allowed to remain for an appreciable time in contact with the flame 
before its particles are raised to the igniting point. It was on this 
principle that Stephenson's original safety lamp was constructed, the 
flame being surrounded with a tall glass chimney, the rapid draught 
through which caused the explosive mixture to be hurried past the flame 
without igniting. 

To illustrate this, a copper funnel holding about two quarts (fig. 99) is employed, 
the neck of which has an opening of about \ inch in diameter. The funnel being 
placed mouth downwards in the pneumatic trough, the orifice is closed with the 
finger, and a half-pint of coal gas passed up into the funnel. The latter is now 
raised from the water, so that it may become entirely filled with air. By depressing 
the funnel to a considerable depth in the water, the aperture being still closed by 
the finger, the mixture will be confined under considerable pressure, and if a lighted 
taper be held to the aperture, and the finger removed, it will be found that the 





Fig. 99. 



Fig. 100. 



mixture sweeps past the flame Avithout exploding, until the water has reached the 
same level in the funnel as in the trough, when the gas comes to rest and explodes 
with great violence. 

Davy's safety lamp (fig. 100) is an application of the principle that 
ignited gas {flame) is extinguished by contact with a large surface of a 
good conductor of heat, such as copper or iron. 

If a thin copper wire be coiled round into a helix, and carefully placed over the 
wick of a burning taper (fig. 101), the flame will be at once extinguished, its heat 
being so rapidly transmitted along the wire that the temperature falls below the 
point at which the combustible gases enter into combination with oxygen, and therefore 
the combustion ceases. If the coil be heated to redness in a spirit-lamp flame before 



PKINCIPLE OF SAFETY LAMPS. 



101 




Fig. 101. 



placing it over the wick, it will not abstract the heat so readily, and will not extin- 
guish the flame. If a copper tube were substituted for the coiled wire, the same result 
would be obtained, and by employing a number of tubes 
of very small diameter, so that the metallic surface may 
be very large in proportion to the volume of ignited gas, 
the most energetic combustion may be arrested, as in the 
case of Hemming 's safety jet, which consists of a brass 
tube tightly stuffed with thin copper wires so as to leave 
very narrow passages, thus rendering it impossible for 
the oxyhydrogen flame at the jet to pass back and ignite 
the mixture in the reservoir. It is evident that the 
exposure of a large extent of cooling surface to the action 
of the flame may be effected either by increasing the 
length or by diminishing the width of the metallic tubes, 

so that wire gauze, which may be regarded as a collection of very short tubes, will 
form an effectual barrier to flame, provided that it has a sufficient number of meshes 
to the inch. 

If a piece of iron wire gauze, containing about 400 meshes to the square inch, be 
depressed upon a flame, it will extinguish that portion with which it is in contact, 
and the combustible gas which escapes through the gauze may be kindled by a lighted 
match held on the upper side. By holding the gauze 2 or 3 inches above a gas jet, 
the gas may be lighted above it without communicating the flame to the burner itself. 

When blazing spirit is poured upon a piece of wire gauze (fig. 102), the flame will 
remain upon the gauze, and the extinguished spirit will pass through. A little 
benzene or turpentine may be added to the spirit, 
so that its flame may be more visible at a distance. 

The safety lamp (fig. 100) is an oil lamp, 
the flame of which is surrounded by a cage 
of iron wire gauze, having 700 or 800 
meshes in the square inch, and made 
double at the top where the heat of the 
flame chiefly plays. This cage is protected 
by stout iron wires attached to a ring for 
suspending the lamp. A brass tube passes 
up through the oil reservoir, and in this Fig- 102. 

there slides, with considerable friction, a wire bent at the top, so that the 
wick may be trimmed without taking off the cage. 

If this lamp be suspended in a large jar, closed at the 
top with a perforated wooden cover A (fig. 103), and 
having an aperture (B) below, through which coal gas is 
allowed to pass slowly into the jar, the flame will be 
seen to waver, to elongate itself very considerably, and 
will be ultimately extinguished, when the wire cage will 
be seen to be filled with a mixture of coal gas and air 
burning tranquilly within the gauze, which prevents the 
flame from passing to ignite the explosive atmosphere 
surrounding the lamp ; that an explosive mixture really 
fills the jar may be readily ascertained by introducing, 
through an aperture (C) in the cover, the unprotected 
flame of a taper, when an explosion will take place. 

This experiment illustrates the action of the Davy 
lamp in a mine which contains fire-damp, and makes it 
evident that this lamp would afford complete protection 
if carefully used. It would obviously be unsafe to allow 
the lamp to remain in the explosive mixture when the cage is filled with flame, for 
the gauze would either become sufficiently heated to kindle the surrounding gas or 
would be oxidised and eaten into holes, which would allow the passage of the flame. 
Nor should the lamp be exposed to a very strong current, which might possibly be 
able to carry the flame through the meshes. 

The great defect of the Davy lamp is that it does not afford more 





Fig. 103. 



102 USE OF THE DAVY LAMP. 

than a glimmering light, so that even if the miners were prohibited 
from employing any candles, they wonld (and experience has proved 
that they do) remove the wire cage at all risks. The lamp has been 
modified so as partially to remove this defect, by substituting glass or 
talc for some portions of the wire gauze. It is now usual, however, to 
employ the Davy lamp merely in order to test the state of the air in the 
different parts of the mine ; for this purpose the firemen descend before 
the commencement of work every morning, and examine with their 
safety lamps every portion of the mine, giving warning to the miners 
not to approach those parts in which any accumulation of fire-damp 
(or technically, " sulphur ") is perceived. The miners then work with 
naked candles, and it appears to be not unusual to see a blue flame (or 
corpse light) playing around the candles, so that the miners may become 
accustomed to regard with little concern the very indication which shows 
that the quantity of fire-damp is only a little below that required to 
form an explosive mixture. Whenever naked flames are used in the 
mine, there must always be great risk ; in most seams of coal there are 
considerable accumulations of fire-damp ; when a fissure is made, the 
gas escapes very rapidly from the blower, and the air in its vicinity may 
soon become converted into an explosive mixture. In mines where 
small quantites of fire-damp are known to be continually escaping from 
the coal, ventilation is depended upon in order to dilute the gas with 
so large a volume of air that it is no longer explosive, and finally to 
sweep it out of the mine ; but it has occasionally happened that the 
ventilation has been interfered with by a door having been left open in 
one of the galleries, or by a passage having been obstructed through the 
accidental falling in of a portion of the coal, and an explosive mixture 
has then been formed. 

Galloway has shown that the presence of fine dust of coal in the air 
of the mine greatly increases the liability to explosion. Most combustible 
substances mixed in a finely divided state with air, burn so rapidly as 
to produce effects of explosion. Flour mills have been destroyed from 
this cause in very dry weather. 

If some lycopodium be placed in a glass funnel, the stem of which has been lightly- 
stopped with wool, and has two or three feet of wide vulcanised tubing attached to 
it, the lycopodium may be blown out in a cloud by a sudden puff of air, and if a 
lighted taper be held in the cloud, an immense volume of flame will be formed. 

(Lycopodium is the seed of the club moss, — Lycopodium clavahtm, — and is used 
for theatrical lightning.) 

An ingenious fire-damp indicator has been constructed of two platinum wires, 
which are heated by a magneto-electric current. One wire is sheltered from the fire- 
damp, and the other, being exposed to it, glows more strongly on account of the slow 
combustion of the fire-damp at the surface of the platinum (see Platinum). By a 
careful comparison of the two wires, it is said that "25 per cent, of marsh gas in air 
may be detected, whilst the Davy lamp will not indicate less than 2 per cent. 

Structure of Flame. 

75. The consideration of the structure and properties of ordinary 
flames is necessarily connected with the history of defiant gas and marsh 
gas. Flame may be defined as gaseous matter heated to the temperature 
at which it becomes visible, or emits light. Solid particles begin, for the 
most part, to emit light when heated to about 1000° F. ; but gases, on 
account of their lower radiating power, must be raised to a far higher 



ILLUMINATING FLAMES. 103 

temperature, and hence the point of visibility is seldom attained, except 
by gases which are themselves combustible, and therefore capable of 
producing, by their own combination with atmospheric oxygen, the requi- 
site degree of heat. The presence of a combustible gas (or vapour), 
therefore, is one of the conditions of the existence of name ; a diamond, 
or a piece of thoroughly carbonised charcoal, will burn in oxygen with 
a steady glow, but without name, since the carbon is not capable of con- 
version into vapour, while sulphur burns with a voluminous flame, in 
consequence of the facility with which it assumes the vaporous condition. 
It will be observed, moreover, that in the case of a non-volatile combus- 
tible, the combination with oxygen is confined to the surface of contact, 
whilst in the flame of a gas or vapour the combustion extends to a con- 
siderable depth, the oxygen intermingling with the gaseous fuel. 

Flames may be conveniently spoken of as simple or compound, accord- 
ingly as they involve one or more phenomena of combustion ; thus, for 
example, the flames of hydrogen and carbonic oxide are simple, whilst 
those of marsh gas and olefiant gas are compound, since they involve both 
the conversion of hydrogen into water and of carbon into carbon dioxide. 

It is obvious that simple flames must be hollow in ordinary cases, 
such as that of a gas issuing from a tube into the air, the hollow being 
occupied by the combustible gas to which the oxygen does not penetrate. 

All the names which are ordinarily turned to useful account are com- 
pound flames, and involve several distinct phenomena. Before examining 
these more particularly, it will be advantageous to point out the conditions 
which regulate the luminosity of flames. 

In order that a flame may emit a brilliant light, it is essential that it 
should contain particles which, either from their own nature, or from the 
conditions under which they are placed, do not admit of indefinite ex- 
pansion by the heat of the flame, but are capable of being heated to 
incandescence. Thus the flame of the oxyhydrogen blowpipe (p. 39) emits 
a very pale light, but if the mixture of oxygen and hydrogen be restrained 
from expanding when fired, as in the Cavendish eudiometer (p. 34), it 
gives a bright flash ; or if the flame be directed upon some solid body 
little affected by the heat, such as lime, the light is very intense. 

Phosphorus and arsenic burn with very luminous flames, in consequence 
of the formation of very dense vapours of phosphoric and arsenious oxides 
during the combustion ; the density of the vapours being here attended 
with the same result as that produced by the restrained expansion of the 
steam formed in the Cavendish eudiometer. 

It is not necessary that the incandescent matter should 
be a product of the combustion ; any extraneous solid in 
a finely-divided state will confer illuminating power upon 
a flame. Thus the flame of hydrogen may be rendered 
highly luminous by blowing a little very fine charcoal 
powder into it, from the bottle represented in fig. 104. 

The luminosity of all ordinary flames is due to the 
presence of highly heated carbon in a state of very 
minute division, and it remains to consider the changes 
by which this finely-divided carbon is separated in the Fig. 104. 

flame. 

A candle, a lamp, and a gas burner, exhibit contrivances for procuring 
light artificially in different degrees of complexity, the candle being the 




104 



STRUCTURE OF FLAME. 



most complex of the three. When a new candle is lighted, the first 
portion of the wick is burnt away until the heat reaches that part which 
is saturated with the wax or tallow of which the candle is composed ; 
this wax or tallow then undergoes destructive distillation, yielding a 
variety of products, among which olefiant gas is found in abundance. 
The flame furnished by the combustion of these products melts 
the fuel around the base of the wick, through which it then 
mounts by capillary attraction, to be decomposed in its turn, 
and to furnish fresh gases for the maintenance of the flame. 
In a lamp, the fuel being liquid at the commencement, the 
process of fusion is dispensed with ; and in a gas burner, where 
the fuel is supplied in a gaseous form, the process of destructive 
distillation has been already carried on at a distance. It will 
be seen, however, that the final result is similar in all three 
cases, the flame being maintained by such gases as acetylene, 
marsh gas, and olefiant gas arising from the destructive distilla- 
tion of wax, tallow, oil, coal, &c. 

On examining an ordinary flame, that of a candle, for instance, 
it is seen to consist of three concentric cones (fig. 105), the 
innermost around the wick, appearing almost black, the next 
emitting a bright white light, and the outermost being so pale as to be 
scarcely visible in broad daylight. 

The dark innermost cone consists 
$ merely of the gaseous combustible to 

| which the air does not penetrate, and 

1 which is therefore not in a state of 

combustion. 

The nature of this cone is easily shown by 
experiment : a strip of cardboard held across 
the flame near its base will not burn in the 
centre where it traverses the innermost cone ; 
a piece of wire gauze depressed upon the flame 
near the wick (fig. 106) will allow the passage 
of the combustible gas, which may be kindled 
above it. The gas may be conveyed out of the 
flame by means of a glass tube, inserted into 

the innermost cone, and may be kindled at the other extremity of the tube, which 

should be inclined downwards (fig. 107). 



Fig. 105. 




Fig. 106. 




Fig. 107. 

A piece of phosphorus in a small spoon held in the interior of the flame of a spirit- 
lamp will melt and boil, but will not burn unless it be removed from the flame, and 
may then be extinguished hy replacing it in the flame. 



EXPERIMENTS OX FLAME. 



105 




The combustible gas from the interior of a flame may be collected in a flask (fig. 
108) furnished with two tubes, one of which (A) is drawn out to a point for insertion 
into the flame, whilst the other (B), which passes to the 
bottom of the flask, is bent over and prolonged by a piece 
of vulcanised tubing so that it may act as a siphon. The 
flask is filled up with water, the jet inserted into the interior 
of a flame, and the siphon set running by exhausting it with 
the mouth. As the water flows out through the siphon, the 
gas is drawn into the flask, and after removing the tube 
from the flame, the gas may be expelled by blowing down 
the siphon tube, and may be burnt at the jet. When a 
candle is used for this experiment, some solid products of 
destructive distillation will be found condensed in the flask. 

In the second or luminous cone, combustion is ^is. 108. 

taking place, but it is by no means perfect, being 

attended by the separation of a quantity of carbon, which confers lumi- 
nosity upon this part of the flame. The presence of free carbon is shown 
by depressing a piece of porcelain upon this cone, when a black film of 
soot is deposited. The liberation of the carbon is due to the decomposi- 
tion of the olefiant gas and similar hydrocarbons by the heat, which 
separates the carbon from the hydrogen, and this latter undergoing 
combustion evolves sufficient heat to raise the separated carbon to a white 
heat, the supply of air which penetrates into this portion of the flame 
being insufficient to effect the combustion of the whole of the carbon. 

Some very simple experiments will illustrate the nature of the luminous portion of 
flame. 

Over an ordinary candle flame (fig. 109) a tube may be adjusted so as to convey 
the finely divided carbon from the luminous part of the flame into the flame of 




Fig. 109. Fig. 110. Fig. ill. 

hydrogen, which will thus be rendered as luminous as the candle flame, the dark 
colour of the carbon being apparent in its passage through the tube. 

A bottle furnished with two straight tubes (fig. 110) is connected with a reservoir 
of hydrogen. One of the tubes is provided with a small piece of wider tube contain- 
ing a tuft of cotton wool. On kindling the gas at the orifice of each tube, no differ- 
ence will be seen in the flames until a drop of benzene (C 6 H 6 ) is placed upon the 
cotton, when its vapour, mingling with the hydrogen, will furnish enough carbon to 
render the flame brilliantly luminous. 

Fig. Ill shows a more convenient apparatus for the same purpose ; the hydrogen 



106 



EXPERIMENTS ON FLAME. 



"being passed in through c, burns from the tube a with non-luminous flame, and 
from the tube b, after passing over a piece of cotton moistened with benzene, with a 
luminous flame. 

The pale outermost cone, or mantle, of the flame, in which the separated 
carbon is finally consumed, may be termed the cone of perfect combustion, 
and is much thinner than the luminous cone, the supply of air to this 
external shell of flame being unlimited, and the combustion therefore 
speedily effected. 

The mantle of the flame may be rendered more visible by burning a little sodium 
near the flame, when the mantle is tinged strongly yellow. 

By means of a siphon about one-third of an inch in diameter (fig. 112), the nature 
of the different portions of an ordinary candle flame may be very elegantly shown. 
If the orifice of the siphon be brought just over the 
extremity of the wick, the combustible gases and 
vapours will pass through it, and may be collected in a 
small flask, where they can be kindled by a taper. 
On raising the orifice into the luminous portion of the 
flame, voluminous clouds of black smoke will pour over 
into the flask, and if the siphon be now raised a little 
above the point of the flame, carbonic acid gas can be 
collected in the flask, and may be recognised by shaking 
with lime-water. 

The reciprocal nature of the relation between the 
combustible gas and the air which supports its combus- 
tion, may be illustrated in a striking manner by burning 
a jet of air in an atmosphere of coal gas. 
A quart glass globe with three necks is connected at A (fig. 113) with the gas-pipe 
by a vulcanised tube. The second neck (B), at the upper part of the globe, is con- 
nected by a short piece of vulcanised tube with a piece ol glass tube about \ inch 
wide, from which the gas may be burnt. Into the third and lowermost neck is 




Fig. 112. 





Fig. 113. — Air burning in Fig. 114. — To make a three-necked flask, 

coal gas. 

inserted, by means of a cork, a thin brass tube C (an old cork-borer), about \ inch 
in diameter. When the gas is turned on, it may be lighted at the upper neck ; and 
if a lighted match be then quickly thrust up the tube C, the air which enters it will 
take fire, and burn inside the globe. 

A very inexpensive apparatus for this purpose may be constructed from a common 
Florence oil-flask. By applying a blowpipe flame at A (fig. 114), so as to heat to 
whiteness a spot as large as a threepenny-piece, and quickly blowing into the neck 
of the flask, the heated portion of. the glass may be made to bulge out. A similar 
protuberance is then to be formed at B. A sharp-pointed flame is directed upon A, 
and the glass burst by blowing into the flask whilst it is still exposed to the flame. 
By fusing the edges of the hole thus produced, and turning them outwards with the 
end of a file, a short neck may be formed capable of receiving a cork. When this is 
cool, it is closed with a cork, and a second similar neck is produced at B. 



GAS BUHNERS. 



107 




Fig. 115. — -Argand burner. 



From this review of the structure of flame, it is evident that, in order 
to secure a name which shall be useful for illumination, attention must 
be paid to the supply of oxygen (or air), and to the composition of the 
fuel employed. The use of the chimney of an Argand burner (fig. 115) 
affords an instance of the necessity for attention 
to the proper supply of air. Without the 
chimney, the flame is red at the edges, and 
smoky, for the supply of air is not sufficient to 
consume the whole of the carbon which is 
separated, and the temperature is not competent 
to raise it to a bright white heat, defects which 
are remedied as soon as the chimney is placed 
over it and the rapidly-ascending heated column 
of air draws in a liberal supply beneath the 
burner, as indicated by the arrows. 

By using two chimneys, and causing the air 
to pass down between them, so as to be heated 
to about 500° F. before reaching the flame, an 
equal amount of light may be obtained from a 
much smaller supply of gas. 

The smokeless gas burners employed in laboratories and kitchens exhibit 
the result of mixing the gas with a considerable proportion of air before 
burning it, the luminous part of the flame then entirely disappearing, with 
great augmentation of the temperature of the flame, 
since the carbon is burnt simultaneously with the 
hydrogen, and the size of the flame is diminished. 

The most efficient burner of this kind {Bunsen's burner, 
fig. 116) is that in which the gas is conveyed through a 
narrow jet into a wide tube, at the base of which there are 
four large holes for the admission of air. When a good 
supply of gas is turned on, a quantity of air, about twice the 
volume of the gas, is drawn in through the lower apertures, 
and the mixture of air and gas may be kindled at the orifice 
of the wide tube, its rapid motion preventing the flame from 
passing down within the tube. This tube is sometimes 
surmounted by a rosette burner to distribute the flame, 
with the fingers, a luminous flame is at once produced. 

The luminosity of the flame may also be destroyed by supplying nitrogen instead 
of air to the Bunsen burner, when the diminution of light is due partly to the 
increased area of the flame and partly to the cooling effect of the nitrogen. 

The temperature of the Bunsen flame is estimated to be 1200° C. in the inner blue 
flame, and 1350° C. in the outer layer or mantle of the flame. 

The gauze burner (fig. 117) consists of an open cylinder 
surmounted by wire gauze. When this is placed over the 
gas burner, a supply of air is drawn in at the bottom by the 
ascending stream of gas, and the mixture burns above the 
gauze with a very hot smokeless flame, the metallic meshes 
preventing the flame from passing down to the gas below. 

The luminosity of a flame is materially affected 
by the pressure of the atmosphere in which it burns, 
a diminution of pressure causing a loss of illuminat- 
ing power. If the light of a given flame burning 
in the air when the barometer stands at 30 inches 
be represented by 100, each diminution of one 
inch in the height of the barometer will reduce the luminosity by five ; 




Fig. 116. — Bunsen's 
burner. 



By closing the air-holes 




f%0m 



Fig. 117.— Gauze 
burner. 



108 



COMPOSITION OF ILLUMINATING FUEL. 



and conversely, when the barometer rises one inch, the luminosity 
will be increased by five. This is not due to any difference in the rate 
of burning, which remains pretty constant, but to the more complete 
interpenetration of the rarefied air and the gases composing the flame; 
this gives rise to the separation of a smaller quantity of incandescent 
carbon. In air at a pressure of 120 inches of mercury, the flame of 
alcohol is highly luminous, the high density of the air discouraging the 
intermixture of the flame gases with it, and thus allowing the separation 
of a portion of carbon. 

In considering the influence exerted by the composition of the fuel 
upon the character of its flame, it will be necessary to bear in mind that 
some kinds of fuel consist of carbon and hydrogen only, whilst others 
contain a considerable proportion of oxygen. 

The following table exhibits the composition of some of the principal 
substances concerned in producing ordinary illuminating flames : — 



Fuel. 


Formula. 


Carbon. 


Hydrogen. 


Oxygen. 


Marsh gas, . 


CH 4 


30 


10 




Olefiant gas, 






C 2 H 4 


60 


10 




Paraffin, 






C1GH34 


30 


10 




Turpentine, . 






C 10 H 16 


75 


10 




Benzene, 






C 6 H 6 


3 20 


10 




Wax, . 






CW^Oa* 


60 


10 


3'5 


Stearine, 






CWH 110 O 6 


621 


10 


8 7 


Oleine, 






C57H104O6 


65-8 


10 


9-2 


Alcohol, 






C 2 H 6 


40 


10 


27 


Wood naphtha, 






CH 4 


30 


10 


40 



It may be stated generally that when the number of atoms of carbon is 
less than one-third that of hydrogen, the flame will be free from smoke, 
as in the case of marsh gas. When there is more carbon than this, the 
flame is very liable to smoke, unless managed with great judgment. 
Those hydrocarbons which contain, like turpentine, benzene, and the 
paraffin oils, a very large proportion of carbon, 
always burn with much smoke, and require special 
contrivances to render them applicable for illumin- 
ating purposes, such as lamps with tall narrow 
chimneys of peculiar construction to afford a strong 
current of air. Benzene (coal naphtha) vapour 
must be mixed with air if it is required to burn 
with a smokeless flame. 

If a piece of cotton wool, moistened with benzene, be 
placed in a flask provided with two tubes (tig. 118), it will 
be found, on gently warming the flask by dipping it into 
hot water, and blowing through one of the tubes, that the 
mixture of benzene vapour and air issuing from the other 
tube will burn with a smokeless bright flame. 

If coal gas, which is essentially a mixture of hydrogen, marsh gas, and 
olefiant gas, and generally contains rather too much hydrogen in propor- 

* This is the composition of myricine, which forms the greater part of bees' wax. 




Fiff. 118. 



THE BLOWPIPE FLAME. 109 

tion to its carbon, be enriched with carbon by passing over benzene (light 
coal naphtha), or napthalene, it burns with a far more luminous flame 
(naphthalised gas). 

When the fuel contains oxygen, the carbon may exist in larger propor- 
tion to the hydrogen without giving rise to the production of smoke, since 
this oxygen will dispose of a portion of the carbon during the combustion. 
Thus, wax is much less liable to smoke than olefiant gas, although con- 
taining the same proportion of carbon to hydrogen, whilst stearine (the 
chief part of tallow) and oleine (forming the bulk of oils) may be burnt 
in ordinary candles and lamps, although still richer in carbon, because 
they contain more oxygen also. 

Alcohol yields a flame of no illuminating value, although it contains 
more carbon in proportion to its hydrogen than is present in marsh gas, 
because its oxygen helps to consume the carbon during the combustion, 
and prevents it from separating in the incandescent state. By adding 
about one-tenth of its bulk of benzole or turpentine, however, alcohol may 
be made to burn with a brilliant flame. 

76. The blowpipe flame. — The principles already laid down will render 
the structure of the blowpipe flame easily intelligible. It must be 
remembered that in using the blowpipe, the stream of air is not propelled 
from the lungs of the operator (where a great part of its oxygen would 
have been consumed), but simply from the mouth, by the action of the 
muscles of the cheeks. The first apparent effect upon the flame is 
entirely to destroy its luminosity, the free supply of air affecting the 
immediate combustion of the carbon. The size of the flame, moreover, is 
much diminished, and the combustion being concentrated into a smaller 
space, the temperature must be much 
higher at any given point of the 
flame. In structure, the blowpipe 
flame is similar to the ordinary flame, 
consisting of three distinct cones, the 
innermost of which (A, fig. 119) is 
filled with the cool mixture of air and 
combustible gas. The second cone, 
especially at its point (E), is termed Fig< n 9 . —Blowpipe flame, 

the reducing flame, for the supply of 

oxygen at that part is not sufficient to convert the carbon into carbon 
dioxide, but leaves it as carbonic oxide, which speedily reduces almost all 
metallic oxides placed in that part of the flame to the metallic state. 
The outermost cone (0) is called the oxidising flame, for there the supply 
of oxygen from the surrounding ah is unlimited, and any substance prone 
to combine with oxygen at a high temperature is oxidised when exposed 
to the action of that portion of the flame ; the hottest point of the blow- 
pipe flame, where neither fuel nor oxygen is in excess, appears to be a 
very little in advance of the extremity of the second (reducing) cone. 
The difference in the operation of the two flames is readily shown by 
placing a little red lead (oxide of lead) in a shallow cavity scooped upon 
the surface of a piece of charcoal (fig. 120), and directing the flames upon 
it in succession ; the inner flame will reduce a globule of metallic lead, 
which may be reconverted into oxide by exposing it to the outer flame.* 

* By directing the reducing name upon the metallic oxide in the cavity, and allowing 




110 



HOT-BLAST BLOWPIPE. 



The immense service rendered by this instrument to the chemist and 
mineralogist is well known. 

By forcing a stream of oxygen through a flame, from a gas-holder or 
bag, an intensely hot blowpipe flame is obtained, in which pipeclay and 
platinum may be melted, and iron burns with great brilliancy. 





Fig. 121.— Hot-blast blowpipe. 



Fig. 120. — Reduction of metals on charcoal. 
Fletcher's hot-blast blowpipe (fig. 121) produces a much higher temperature than 
the ordinary blowpipe. Coal gas is supplied through the tube g, and is kindled at 

the Bunsen burners b b and at the orifice /, the 
supply to the former being regulated by the stop- 
cock c, and to the latter by the stopcock d. The 
flames of the Bunsen burners heat the spiral copper 
tube e to redness, so that the air blown in through 
the flexible tube a is strongly heated before being 
projected into the flame through a blowpipe jet 
at /. Thin platinum wires melt easily in this 
flame, and thin iron wires burn away rapidly. 

77. Determination of the composition of 
gases containing carbon and hydrogen. — In 
order to ascertain the proportions of carbon 
and hydrogen present in a gas, a measured 
volume of the gas is mixed with an excess of 
oxygen, the volume of the mixture carefully noted, and explosion deter- 
mined by passing the electric spark ; the gas remaining after the explosion 
is measured and shaken with potash, which absorbs the carbonic acid gas 
from the volume of which the proportion of carbon may be calculated. 
Tor example, 

0*4 cubic inch of marsh gas, mixed with 
1*0 „ oxygen, and exploded, left 

0"6 ., gas ; shaken with potash, it left 

0-2 „ oxygen, 

showing that 0*4 cubic inch of carbonic acid gas had been produced, 
quantity of carbonic acid would contain 0*4 cubic inch of oxygen, 
ducting this last from the total amount of oxygen consumed (0*8 cubic 
inch), we have 0'4 cubic inch for the volume of oxygen consumed by the 
hydrogen. Now, 0*4 cubic inch of oxygen would combine with 0*8 cubic 
inch of hydrogen, which represents therefore the amount of hydrogen in 
the marsh gas employed. It has thus been ascertained that the marsh 
gas contains twice its volume of hydrogen. 

Sp. gr. (to H) or weight of 1 volume of marsh gas, . . =8 

weight of 2 volumes (one molecule), . . =16 

2 volumes of marsh gas contain 4 volumes H, weighing . 4 



This 
De- 



2 volumes of marsh gas contain x volume C, weighing 



12 



the oxidising flame to sweep over the surface of the charcoal, as shown in the figure, a 
yellow incrustation of oxide of lead is formed upon the surface of the charcoal, which 
affords additional evidence of the nature of the metal. 



PRODUCTS OF DISTILLATION OF COAL. 



Ill 



^ 



For the purpose of illustration, the analysis of marsh gas maybe effected in a TJre's 
eudiometer (fig. 122), but a considerable excess of oxygen should be added to mode- 
rate the explosion. The eudiometer having been filled 
with water, O'l cubic inch of marsh gas is introduced 
into it, as described at p. 36, and having been transferred 
to the closed limb and accurately measured after equal- 
ising the level of the water, the open limb is again filled 
up with water, the eudiometer inverted in the trough, 
and 1'2 cubic inch of oxygen added; this is also trans- 
ferred to the closed limb and carefully measured. The 
electric spark is passed through the mixture (see p. 
36), the open limb being closed by the thumb. The 
level of the water in both limbs is then equalised, and 
the volume of gas measured. The open limb is filled 
up with a strong solution of potash, and closed by the 
thumb, so that the gas may be transferred from the 
closed to the open limb and back, until its volume is 
no longer diminished by the absorption of carbon dioxide, 
oxygen having been measured, the calculation is effected as 

The results are more exact when the eudiometer is filled with mercury instead of 
water. 




Cy, 



Fig. 122. 
Siphon eudiometer. 

The volume of residual 
above described. 



Coal Gas. 

78. The manufacture of coal gas is one of the most important appli- 
cations of the principle of destructive distillation, and affords an excellent 
example of the tendency of this process to develop new arrangements 
of the elements of a compound body. The action of heat upon coal, in 
a vessel from which air is excluded, gives rise to the production of a very 
large number of compounds containing some two or more of the five 
elements of the coal, in different proportions, or in different forms of 
arrangement. Although no clue has yet been obtained to indicate the 
true arrangement of these elements in the original coal (or, as it is termed, 
the constitution of the coal), it is certain that these various compounds do 
not exist in it before the application of heat, but are really the results of 
its action; that they are indeed "products and not educts. 

The most important forms assumed by the carbon and hydrogen when 
coal is strongly heated, are, — 



/Hydrogen, 
| Marsh gas, 
Gases -{ Olefiantgas, 
| Acetylene, 
L Butylene, 



CH 4 



C 4 H g 



Liquids 



[ Benzene, 
\ Toluene, 



C«H« 



I .f: 



I Naphthalene, C 10 H 8 
t3 J Anthracene, C 14 H 1() 
^ 1 Paraffin, . C 16 H 34 
M [Coke, . . C 



The nitrogen of the coal reappears in the forms 
Gases 5 Nitrogen, 



of- 



I Ammonia, 

i Aniline, 
Quinoline, 
Hydrocyanic acid, 



NH 3 
C 6 H 7 N 
C 9 H 7 N 
CHN 



The oxygen contributes to the production of 

Carbonic oxide, . CO 

Carbon dioxide, . CO, 



Gases 



Liquids 



Alkaline. 



( Water, 

< Acetic acid, . 

( Carbolic acid, 



H o 

c.;h 4 o 2 



Sulphur is found among the products as, 



Sulphuretted hydrogen gas, 



Liquid ) 



(very volatile) \ Carbon bisulphide, CS. 2 , 

The illuminating gas obtained from «oal consists essentially of free hydro- 
gen, marsh gas, olefiant gas, and carbonic oxide, with small quantities of 



112 



COMPOSITION OF COAL GAS. 



acetylene, benzene vapour, and some other substances. Its specific 
gravity is about -4, and varies inversely as its illuminating value. 

A fair general idea of its composition is given by the following table: — 



Gas from Cannel Coal. 



Hydrogen, 
Marsh gas, 
Carbonic oxide, 
Olefiant gas, . 
Carbonic acid gas, 
Nitrogen, 
Oxygen, 



45 '8 47 volumes. 


40'948 


4-167 




5-504 




1-950 




1-445 


f 


0-139 


' 



100-0 



The only constituents which contribute directly to the illuminating 
value of the gas are the marsh gas, olefiant gas, and similar hydrocarbons, 
acetylene, and benzene vapour. 

The most objectionable constituent is the sulphur present as sulphur- 
etted hydrogen and bisulphide of carbon, for this is converted by com- 
bustion into sulphuric acid, which seriously injures pictures, furniture, 
&c. The object of the manufacturer of coal gas is to remove, as far as 
possible, everything from it, except the constituents mentioned as essential, 
and at the same time to obtain as large a volume of gas from a given 
weight of coal as is consistent with good illuminating value. 

The mode of purifying the gas and the general arrangements for its 
manufacture, will be described in a later part of the work. 




Fig. 1 23. —Destructive distillation of coal. 

The destructive distillation of coal may be exhibited with the arrangement repre- 
sented in fig. 123. The solid and liquid products (tar, ammoniacal liquor, &c.) are 
condensed in the globular receiver (A). The first bent tube contains, in one 
limb (B), a piece of red litmus paper to detect ammonia; and in the other (C) 

a piece of paper impregnated with lead acetate, which 
will be blackened by the sulphuretted hydrogen. 
The second bent tube (D) contains enough lime-water 
to fill the bend, which will be rendered milky by the 
carbonic acid gas. The gas is collected over water, 
in the jar E, which is furnished with a jet from 
which the gas may be burnt when forced out by 
depressing the jar in water. 

The presence of acetylene in coal gas may be 
shown by passing the gas from the supply-pipe (A, 
fig. 124), first through a bottle (B) containing a little 
ammonia, then through a bent tube (C) with enough 
water to fill the bend, and a piece of bright sheet 
copper immersed in the water in each limb. After a short time the bright red flakes 
of the copper acetylide will be seen in the water. 




Fnr. 124. 




QUARTZ — SAND — FLINT. 113 



SILICOK 

79. la many of its chemical relations to other bodies, this element 
will be found to bear a great resemblance to carbon; but whilst carbon is 
remarkable for the great variety of compound forms in which it is met 
with in nature, silicon is always found in combination with oxygen, as 
silica (Si0 2 ), either alone or as silicates. 

Silica (Si0 2 = 60 parts by weight). — The purest natural variety of silica 
is the transparent and colourless variety of quartz known as rock crystal, 
the most widely diffused ornament of the mineral world, often seen 
crystallised in beautiful six-sided prisms, terminated by six-sided pyra- 
mids (fig. 125), which are 
always easily distinguished 
by their great hardness, 
scratching glass almost as 
readily as the diamond. 
Coloured of a delicate 
purple, probably by a little 
organic matter, these crys- Fig. 125.— Crystal of quartz, 

tals are known as amethyst; 

and when of a brown colour, as Cairngorm stones or Scotch pebbles Losing 
its transparency and crystalline structure, we meet with silica in the form 
of chalcedony and of carnelian, usually coloured, in the latter, with oxide 
of iron. 

Hardly any substance has so great a share in the lapidary's art as silica, 
for in addition to the above instances of its value for ornamental purposes, 
we find it constituting jasper, agate, cat's eye, onyx, so much prized for 
cameos, opal, and some other precious stones. In opal the silica is com- 
bined with water. 

Sand, of which the whiter varieties are nearly pure silica, appears to 
have been formed by the disintegration of siliceous rocks, and has generally 
a yellow or brown colour, due to the presence of oxide of iron. 

The resistance offered by silica to all impressions has become proverbial 
in the case of flint, which' consists essentially of that substance coloured 
with some impurity. Flints are generally found in compact masses, distri- 
buted in regular beds throughout the chalk formation ; their hardness, 
which even exceeds that of quartz, formerly rendered them useful for 
striking sparks with steel, by detaching small particles of the metal, which 
are so heated by the percussion as to continue to burn (see p. 29) in the 
air, and to inflame tinder or gunpowder upon which they are allowed to 
fall. 

The part taken by silica in natural operations appears to be chiefly a 
mechanical one, for which its stability under ordinary influences peculiarly 
fits it, for it is found to constitute the great bulk of the soil which serves 
as a support and food reservoir of land plants, and enters largely into the 
composition of the greater number of rocks. 

But that this substance is not altogether excluded from any share in 
life, is shown by its presence in the shining outer sheath of the stems of 
the grasses and cereals, particularly in the hard external coating of the 
Dutch rush used for polishing; and this alone would lead to the inference 
that silica could not be absolutely insoluble, since the capillary vessels 
of plants are known to be capable of absorbing only such substances as are 

H 



114 SIRICA RENDERED SOLUBLE. 

in a state of solution. Many natural waters also present us with silica in 
a dissolved state, and often in considerable quantity, as, for example, in 
the Geysers of Iceland, which deposit a coating of silica upon the earth 
around their borders. 

Pure water, however, has no solvent action upon the natural varieties 
of silica. The action of an alkali is required to bring it into a soluble 
form. 

To effect this upon the small scale, a few crystals of common washing- 
soda (sodium carbonate) may be powdered and dried; a little of the dried 
powder is placed upon a piece of platinum foil slightly bent up (fig. 126), 
and is fused by directing the flame of a blowpipe upon the under side of 
the foil. As soon as the carbonate of soda is perfectly liquefied, a small 
quantity of very finely powdered white sand is thrown into it, when brisk 
effervescence will be observed, and the particles of sand will dissolve * 
fresh portions of sand may now be added as long as they produce effer- 
vescence, which is due to the escape of the carbonic acid gas. The piece 
of platinum foil, when cool, may be placed in a little warm water, and 



Fig. 126. — Fusion on platinum foil. 

allowed to soak for some time, when the melted mass will gradually 
dissolve, forming a solution of sodium silicate. This solution will be 
found decidedly alkaline to test-papers. 

If a portion of the solution of sodium silicate in water be poured into 
a test-tube, and two or three drops of hydrochloric acid added to it, with 
occasional agitation, effervescence will be produced by the expulsion of 
any carbonic acid gas still remaining, and the solution will be converted 
into a gelatinous mass by the separation of silicic acid. But if another 
portion of the solution be poured into an excess of dilute hydrochloric 
acid (i.e., into enough to render the solution distinctly acid), the silicic 
acid will remain dissolved in the water, together with the sodium chloride 
formed. 

In order to separate the sodium chloride from the silicic acid, the 
process of dialysis * must be resorted to. 

Dialysis is the separation of dissolved substances from each other by 
taking advantage of the different rates at which they pass through moist 
diaphragms or septet. 

If the mixed solution of sodium chloride and silicic acid were poured 
upon an ordinary paper filter, it would pass through without alteration ; 
but if parchment paper be employed, which is not pervious to water, 
although readily moistened by it, none of the liquid will pass through. 

* From diaXvu), to part asunder. 




DIALYSED SILICA. 115 

If the cone of parchment paper be supported upon a vessel filled with 
distilled water (fig. 127), so that the water may be in contact with the 
outer surface of the cone, the hydrochloric acid and the sodium chloride 
will pass through the substance of the parchment paper, and the water 
charged with them may be seen descending in dense 
streams from the outside of the cone. After a few hours, 
especially if the water be changed occasionally, the whole 
of the hydrochloric acid and sodium chloride will have 
passed through, and a pure solution of silicic acid in water 
will remain in the cone. 

This solution of silicic acid is very feebly acid to blue 
Jitmus paper, and not perceptibly sour to the taste. It 
has a great tendency to set into a jelly in consequence of 
the sudden separation of silicic acid. If it be slowly 
evaporated in a dish, it soon solidifies ; but, by conducting 
the evaporation in a flask so as to prevent any drying of pj„ 12 7. 

the silicic acid at the edges of the liquid, it may be 
concentrated until it contains 14 per cent, of silicic acid. When this 
solution is kept, even in a stoppered or corked bottle, it sets into a trans- 
parent gelatinous mass, which gradually shrinks and separates from the 
water. When evaporated, in vacuo, over sulphuric acid, it gives a trans- 
parent lustrous glass which is composed of 22 per cent, of water and 78 
per cent, of silica (H 2 O.Si0 2 ). 

This hydrate of silica cannot be redissolved in water, and is only soluble 
to a slight extent in hydrochloric acid. If it be heated to expel the water, 
the silica which remains is insoluble both in water and in hydrochloric 
acid, but is dissolved when boiled with solution of potash or soda, or their 
carbonates. 

Silica in the naturally crystallised form, as rock crystal and quartz, 
is insoluble in boiling solutions of the alkalies, and in all acids except 
hydrofluoric ; but amorphous silica (such as that found at Farnham) is 
readily dissolved by boiling alkalies. These represent, in fact, two dis- 
tinct modifications of silica. A transparent piece of rock crystal may be 
heated to bright redness without change, but if it be powdered previously 
to being heated, its specific gravity is diminished from 2*6 to 2*4, and it 
becomes soluble in boiling alkalies, having been converted into the amor- 
phous modification. 

Crystals of quartz have been obtained artificially by the prolonged 
action of water upon glass at a high temperature under pressure. When 
fused with the oxy hydrogen blowpipe, silica does not crystallise, being 
thus converted into the amorphous variety of sp. gr. 2*3. 

To prepare the amorphous modification of silica artificially, white sand in very 
fine powder may be fused, in a platinum crucible, with six times its weight of a mix- 
ture of equal weigbts of the potassium and sodium carbonates, the mixture being 
more easily fusible than either of the carbonates separately. The crucible may be 
heated over a gas burner supplied with a mixture of gas and air, or may be placed in 
a little calcined magnesia contained in a fireclay crucible, which may be covered up 
and introduced into a good fire. The platinum crucible is never heated in direct 
contact with fuel, since the metal would become brittle by combining with carbon, 
silicon, and sulphur derived from the fuel. The magnesia is used to protect the 
platinum from contact with tbe clay crucible. When the action of the silica upon 
tbe alkaline carbonates is completed, which will be indicated by the cessation of the 
effervescence, the platinum crucible is allowed to cool, placed in an evaporating dish, 
and soaked for a night in water, when the mass should be entirelv dissolved. Hydro- 



116 



ACID CHARACTER OF SILICA. 




Fig. 128. 



chloric acid is then added to the solution, with occasional stirring, nntil it is distinctly 
acid to litmus paper. On evaporating the solution, it will, at a certain point, solidify 
to a gelatinous mass of hydrated silica, which would be 
spirted out of the dish if evaporation over the flame were 
continued. To prevent this, the dish is placed over an 
empty iron saucepan (fig. 128) so that the heat from' the 
flame may be equally distributed over the bottom of the 
dish. When the mass is quite dry, the dish is allowed to 
cool, and some water is poured into it, which dissolves 
the chlorides of potassium and sodium (formed by the 
action of the hydrochloric acid upon the silicates), and 
leaves the silica in white flakes. These may be collected 
upon a filter (fig. 129), and washed several times with 
distilled water. The filter is then carefully spread out 
upon a hot iron plate, or upon a hot brick, and allowed 
to dry, when the silica is left as a dazzling white powder, 
which must be strongly heated in a porcelain or platinum 
crucible to expel the last traces of water. It is remarkable for its extreme lightness, 
especially when heated, the slightest current of air easily blowing it away. 

80. For effecting such fusions as that 
just described, an air-gas blowpipe (A, fig. 
130) supplied with air from a double action 
bellows (B), worked by a treadle (C), will 
be found most convenient. Where gas is 
not at hand, the fusion may be effected 
in a small furnace (fig. 131), surmounted 
with a conical chimney, and fed with 
charcoal. 

81. Silicates. — The acid proper- 
ties of silicic acid are so feeble that 
it is a matter of great difficulty to 
determine the proportion of any base 
which is required to react with it in 
order to form a chemically neutral 
salt. Like carbonic acid, it does not 
destroy the action of the alkalies 
upon test-papers, and we are there- 
fore deprived of this method of 
ascertaining the proportion of alkali 
which neutralises it in a chemical 
sense. In attempting to ascertain 

the quantity of alkali with which silica combines, from that of the carbon 
dioxide which it expels when heated with an alkaline carbonate, it is 
found that the proportion of carbon dioxide expelled varies considerably, 
according to the temperature and the proportion of alkaline carbonate 
employed. 

By heating silica with, sodium hydrate (NaHO), it is found that 60 
parts of silica expel 36 parts of water, however much sodium hydrate is 
employed, and the same proportion of water is expelled from barium 
hydrate Ba(HO) 2 when heated with silica. 

The formula Si0 2 represents 60 parts by weight of silica, and 36 parts 
represent two molecules of water. Hence it would appear that the action 
of silica upon sodium hydrate is represented by the equation, 4jNTaHO 
+ Si0 2 = Na 4 Si0 4 + 2H 2 0; and that upon barium hydrate by 2Ba(HO) 2 
+ Si0 9 = Ba 2 Si0 4 + 2H 2 : and since it is found that several of the crystal- 
lised mineral silicates contain a quantity of metal equivalent to H 4 , it is 




Fig. 129. — Washing precipitate. 



SILICON. 



117 



usual to represent silicic acid as a tetrabasic acid, H 4 Si0 4 , containing 
4 atoms of hydrogen which may be replaced by metals. 

The circumstance that silica is not capable of being converted into 
vapour at a high temperature, enables it to decompose the salts of many 
acids which, at ordinary temperatures, are able to displace silicic acid. 

The silicates form by far the greatest number of minerals. The 
different varieties of clay consist of aluminium silicate; felspar is a silicate 
of aluminium and potassium; meerschaum is a silicate of magnesium. 

The different kinds of glass are composed of silicates of potassium, 
sodium, calcium, lead, &c. 

None but the silicates of the alkali metals are soluble in water. 

Scarcely any of the silicates are represented by formulae which express 
their derivation from the acid H 4 Si0 4 ; they are mostly irregular com- 
binations of metallic oxides with Si0 o . 





Air-gas blowpipe table. 



Fig. 131.. — Charcoal furnace. 



82. Silicon or silicium (Si = 28 parts by weight). — From the remarkably 
unchangeable character of silica, it is not surprising that it was long re- 
garded as an elementary substance. In 1813, however, Davy succeeded in 
decomposing it by the action of potassium, and in obtaining an impure 
specimen of silicon. It has since been produced, far more easily, by con- 
verting the silica into potassium silico-fluoride (K 2 SiF 6 ), and decomposing 
this at a high temperature with potassium or sodium, which combines 
with the fluorine to form a salt capable of being dissolved out by water, 
leaving the silicon in the form of a brown powder (amorphous silicon), 
which resists the action of all acids, except hydrofluoric, which it decomposes, 
forming silicon fluoride, and evolving hydrogen (Si + 4HF = SiF 4 + H 4 ). 
It is also dissolved by solution of potash, with evolution of hydrogen, and 
formation of potassium silicate. It burns brilliantly when heated in 
oxygen, but not completely, for it becomes coated with silica which is 
fused by the intense heat of the combustion. When heated with the 
blowpipe on platinum foil, it eats a hole through the metal, with which 
it forms the fusible platinum silicide. 

If potassium silico-fluoride be fused with aluminium, a portion of the 



118 CHEMICAL RELATIONS OF SILICON. 

latter combines with tlie fluorine, and the remainder combines with the 
silicon, forming aluminium silicide. By boiling this with hydrochloric and 
hydrofluoric acids in succession, the aluminium is extracted, and crystalline 
scales of silicon, with a metallic lustre resembling black lead, are left 
(graphitoid silicon). In this form the silicon has a specific gravity of 
about 2*5, and refuses to burn in oxygen, or to dissolve in hydrofluoric 
acid. A mixture of nitric and hydrofluoric acids, however, is capable of 
dissolving it. Like graphite, this variety of silicon conducts electricity, 
though amorphous silicon is a non-conductor. The amorphous silicon 
becomes converted into this incombustible and insoluble form under the 
action of intense heat. It is worthy of remark that the combustibility .of 
amorphous carbon (charcoal) is also very much diminished by exposure 
to a high temperature. 

Unlike carbon, however, silicon. is capable of being fused at a tempera- 
ture somewhat above the melting-point of cast-iron ; on cooling, it forms 
a brilliant metallic-looking mass, which may be obtained, by certain pro- 
cesses, crystallised in octahedra so hard as to scratch glass like a diamond. 

In their chemical relations to other substances there is much resem- 
blance between silicon and carbon. Silicon, however, is capable of 
displacing carbon, for if potassium carbonate be fused with silicon, the 
latter is dissolved, forming potassium silicate, and carbon is separated. 
Silicon also resembles carbon in its disposition to unite with certain metals 
to form compounds which still retain their metallic appearance. Thus 
silicon is found together with carbon in cast-iron, and it unites directly 
with aluminium, zinc, and platinum, to form compounds resembling 
metallic alloys. Nitrogen enters into direct union with silicon at a high 
temperature, though it refuses to unite with carbon except in the presence 
of alkalies. 

Silicon nitride (SiN) has been obtained by heating silica with carbon in a blast 
furnace, and treating the product successively with hydrofluoric acid and potash, when 
the nitride is left as a green infusible powder which is attacked by potash at a red 
heat, yielding potassium silicate, hydrogen, and ammonia. When heated in chlorine, 
it is converted into a white substance soluble in hydrofluoric acid, and apparently 
containing Si 3 N" 4 . A similar body is also formed in the preparation of the green 
nitride. 

In their relation to hydrogen, carbon and silicon are widely different, 
for silicon is only known to form one compound with hydrogen, and that 
of a very unstable character. 

The silicon hydride has been found to have a composition corresponding 
with the formula SiH 4 . It derives its interest chiefly from the property 
of taking fire spontaneously in contact with the air; in which it burns 
with a brilliant white flame, giving off clouds of silica, and depositing a 
brown film of silicon upon a cold surface. 

Silicon hydride is prepared by decomposing magnesium silicide with dilute hydro- 
chloric acid. The magnesium silicide is obtained by fusing magnesium chloride (MgCl 2 ) 
with sodium silico-fluoride (Na 2 SiF 6 ), and metallic sodium, when the latter combines 
with the chlorine and fluorine, leaving the magnesium free to unite with the silicon. 

The magnesium chloride may be prepared by dissolving ordinary magnesium 
carbonate in hydrochloric acid; adding three parts of ammonium chloride for each 
part of carbonate, evaporating to dryness in a porcelain dish, fusing the residue, and 
pouring it out on to a clean stone. Being very deliquescent, it must be kept in a 
well-closed bottle. 

Sodium silico-fluoride is made by neutralising hydro-fluosilicic acid with sodium 
carbonate, and evaporating to dryness. 



HYDRIDE- OF SILICON. 



119 



' To increase the fusibility of the mixture, some fused common salt will be required. 
Dried salt may be melted in a fireclay crucible, at a bright red heat, and poured out 
upon a clean dry stone. 

Eight parts of the magnesium chloride, 7 of sodium silico-fiuoride, 2 of fused 
chloride of sodium, and 4 of sodium in slices, are rapidly weighed, shaken together 
in a dry bottle, and thrown into a red hot clay crucible, which is then covered and 
heated as long as the yellow flame of sodium vapour is perceptible. After cooling, 
the crucible is broken, when a dark-coloured layer of magnesium silicide will be found 
beneath a white layer of chloride and fluoride of sodium. The silicide must be 
rapidly detached, and preserved in a well-stopped bottle. 

The magnesium silicide is coarsely powdered, and introduced into a Woulfe's 
bottle (fig. 132) provided with a funnel tube, and a short wide tube for delivering 
the gas. The bottle is filled up with water (previously 
boiled to expel air, and allowed to cool), and placed in 
the pneumatic trough (containing boiled water), so 
that both bottle and tubes may remain filled with 
water. A gas-jar, filled with boiled water, having been 
placed over the delivery -tube, some strong hydrochloric 
acid is added through the funnel, great care being taken 
that no air shall enter. The silicon hydride is at once 
evolved, and must be allowed to stand over water for 
some little time, to allow the froth, caused by a slight 
separation of silica, to subside. The gas may then be 
transferred to a capped jar, with a stopcock, from 
which it may be allowed to pass into the air for the 
examination of its flame. 

"When cast-iron, containing silicon, is boiled with 
hydrochloric acid until the whole of the iron is dis- 
solved, a grey frothy residue is left. If this be collected on a filter, well washed and 
dried, it is found to consist of black scales of graphite, mixed with a very light 
white powder. On boiling it with potash, hydrogen is evolved and the white powder 
dissolves, forming a solution containing potassium silicate. This white powder appears 
to be identical with a substance obtained by other processes, and called leucone * 
which is believed to have the composition Si 3 H 4 5 , and has been regarded as a 
hydrate of protoxide of silicon, 3Si0.2H 2 0. Its action upon solution of potash would 
be explained by the equation — 

Si 3 H 4 5 + 12KHO = 3K 4 Si0 4 + H 6 + 5H 2 0. 
Leucone is slowly converted into silicic acid, even by the action of water, hydrogen 
being disengaged. 

Another compound, containing silicon, hydrogen, and oxygen, has been named 
silicone. It is a yellow substance, the general characters of which resemble those of 
the compound last described. When exposed, under water, to the action of sunlight, 
hydrogen is evolved, and the yellow body becomes converted into leucone. 




lig. 132. 



BOROK 

83. Closely allied to silicon is another element, boron, which has at 
present never been found in animal or vegetable bodies, but appears to 
be entirely confined to the mineral kingdom. 

Anhydrous Boracic Acid (£203 = 69*8 parts by weight). — A saline sub- 
stance called borax (Xa 2 B 4 7 . 10 Aq.) has long been used in medicine, 
in working metals, and in making imitations of precious stones ; this 
substance was originally imported from India and Thibet, where it was 
obtained in crystals from the waters of certain lakes, and came into this 
country under the native designation of tinccd, consisting of impure borax, 
surrounded with a peculiar soapy substance, which the refiner of borax 
makes it his business to remove. 

In 1702, in the course of one of those experiments to which, though 
empirical in their nature, scientific chemistry is now so deeply indebted, 

* AeuKos, white. 



120 



BOEON. 



Homberg happened to distil a mixture of borax and green vitriol (ferrous 
sulphate), when he obtained a new substance in pearly plates, which was 
found useful in medicine, and received the name of sedative salt. A 
quarter of a century later, Lemery found that this substance might be 
separated from borax by employing sulphuric acid instead of ferrous 
sulphate ; but another quarter of a century elapsed before it was shown 
that in borax these pearly crystalline scales were combined with soda, and 
were possessed of acid properties which entitled them to receive the name 
boracic acid. 

Much more recently this acid has been obtained in a free state from 
natural sources, and is now largely imported into this country from the 
volcanic districts in the north of Italy, where it issues from the earth in 
the form of vapour, accompanied by violent jets of steam, which are 
known in the neighbourhood as soffioni. It would appear easy enough, 
by adopting arrangements for the condensation of this steam, to obtain the 
boracic acid which accompanies it, but it is found necessary to cause the 
steam to deposit its boracic acid by passing it through water, for w^hich 
purpose basins of brickwork (lagunes, fig. 133) are built up around the 
soffioni, and are kept filled with water from the neighbouring springs or 




Fig. 133. — Boracic lagune and evaporating pans. 

brooks ; this water is allowed to flow successively into the different lagunes, 
which are built upon a declivity for that purpose, and it thus becomes 
impregnated with about 1 per cent, of boracic acid. The necessity for 
expelling a large proportion of this water, in order to obtain the boracic 
acid in crystals, formed for a long time a great obstacle to the success of 
this branch of industry in a country where fuel is very expensive. In 
1817, however, Larderello conceived the project of evaporating this water 
by the steam-heat afforded by the soffioni themselves, and several hundred 
tons of boracic acid are now annually produced in this manner. The 
evaporation is conducted in shallow leaden evaporating pans (A, fig. 133), 
under which the steam from the soffioni is conducted through the flues (F) 
constructed for that purpose. As the demand for boracic acid increased 
on account of the immense consumption of borax in the porcelain manu- 
facture, the experiment was made, with success, of boring into the volcanic 
strata, and thus producing artificial soffioni, yielding boracic acid. 

The crystals of boracic acid, as imported from these sources, contain 
salts of ammonia and other impurities. They dissolve in about three 
times their weight of boiling water, and crystallise out on cooling, since 



BORACIC ACID. 121 

they require 26 parts of cold water to dissolve them. These crystals are 
represented by the formula 3H 2 O.B 2 3 (or H 3 B0 3 ). If they are sharply 
heated in a retort, they partly distil over unchanged, together with the 
water derived from the. decomposition of another part ; but if they be 
heated to 212° F. only, they effloresce, and become converted into 
H 2 O.B 2 3 . When this is further heated, the whole of the water passes off, 
carrying with it a little boracic acid, and the B 2 3 fuses to a glass, which 
remains perfectly transparent on cooling [vitreous boracic acid). This is 
slowly volatilised by the continued action of a very high temperature. It 
dissolves very slowly in water. Boracic acid is an antiseptic, i.e., it 
hinders putrefaction, and is applied either alone or in combination with 
glycerine, for the preservation of milk, meat, and other foods. It is also 
said to kill grass. 

A characteristic property of boracic acid is that of imparting a green 
colour to names. Its presence may thus be detected in the steam issuing 
from a boiling solution of boracic acid in water ; for if a spirit-lamp flame 
or a piece of burning paper be held in the steam, the flame will acquire a 
green tint, especially at the edges. 

The colour is more distinctly seen when the crystallised boracic acid is heated on 
platinum foil in a spirit-flame or an air-gas flame ; and still better when the crystals 
are dissolved in boiling alcohol, and the solution burnt on a plate. The presence of 
boracic acid in borax may be ascertained by mixing the solution of borax with strong 
sulphuric acid to liberate the boracic acid, and adding enough alcohol to make the 
mixture burn. Another peculiar property of boracic acid is its action upon turmeric. 
If a piece of turmeric paper be dipped in solution of boracic acid and dried at a gentle 
heat, it assumes a fine brown-red colour, which is changed to green or blue by potash 
or its carbonate. In applying this test to borax, the solution is slightly acidified 
with hydrochloric acid, to set free the boracic acid, before dipping the paper. 

Borates. — Boracic acid, like silicic, must b'e classed among the feeble 
acids. It colours litmus violet only, like carbonic acid, and does not 
neutralise the action of the alkalies upon test-papers. At high tempera- 
tures, fused boracic anhydride combines with the alkalies and metallic 
oxides to form transparent glassy borates, which have, in many cases, very 
brilliant colours, and upon this property depend the chief uses of boracic 
acid in the arts. 

Unlike the silicates, the borates are comparatively rare in the mineral 
world. No very familiar mineral substance contains boracic acid. A 
double borate of sodium and calcium, called horo-natrocalcite (jSTa 2 B 4 7 . 
Ca 2 B 8 0i 4 .18H 2 0), is imported from Peru for the manufacture of borax, 
and the mineral known as boracite is a magnesium borate. 

In determining the proportion of base which boracic acid requires to 
form a chemically neutral salt, the same difficulties are met with as in the 
case of silicic acid (p. 116); but since it is found that 69 - 8 parts of 
boracic anhydride (the weight represented by B 2 3 ) displace 54 parts of 
water (three molecules) from sodium hydrate and from barium hydrate, 
both employed in excess, it would appear that the boracic acid requires 
three molecules of an alkali fully to satisfy its acid character. 

The action of B 2 3 upon an excess of NaHO would be represented by 
the equation 6NaHO + B 2 3 = 2Na 3 B0 3 + 3H 2 0. Hence boracic acid is 
a tribasic acid * represented by the formula HgBOg, which is the composi- 
tion of the crystallised acid, but the formulae of the common borates 
cannot be made to accord with this view. 

* A tribasic acid is one which contains three atoms of hydrogen replaceable by metals. 



122 DIAMOND OF BORON. 

84. Boron (B-10'9 parts by weight). — It was in 'the year 1808 that 
Gay-Lussac and Thenard succeeded, by fusing boracic anhydride with 
potassium, in extracting from it the element boron, as an olive-green 
powder {amorphous boron), which has a general, resemblance to silicon, 
but, unlike that element, may be oxidised by nitric acid. It also requires 
a higher temperature to fuse it than is required by silicon. The brilliant 
copper-coloured scales obtained by a process similar to that which fur- 
nishes the grapbitoid silicon, and formerly regarded as graphitoid boron, 
consist really of a compound of boron with aluminium (A1B 2 ). 

The most remarkable form of boron is the crystallised variety or diamond 
of boron, which is obtained by very strongly heating amorphous boron 
with aluminium, and afterwards extracting the aluminium from the mass 
with hydrochloric acid. These crystals are brilliant transparent octahedra, 
which are sometimes nearly colourless, and resemble the diamond in their 
power of refracting light, and in their hardness, which is so grea,t that 
they will scratch rubies, and will even wear away the surface of the 
diamond.* This form of boron cannot be attacked by any acid, but is 
dissolved by fused alkalies. The flame of the oxyhydrogen blowpipe does 
not fuse it, and it only undergoes superficial conversion into boracic 
anhydride when heated to whiteness in oxygen. When heated to redness 
in chlorine, however, it burns, forming boron trichloride. Boron closely 
resembles silicon in its chemical relations to the other elements. It forms 
a compound with hydrogen which is a spontaneously inflammable gas, burn- 
ing with a green flame, and obtained by heating fused boracic anhydride 
with magnesium and treating the mass with hydrochloric acid. Boron 
shows greater disposition to combine with nitrogen than is manifested by 
silicon. It absorbs nitrogen readily when heated to redness, forming a 
white infusible insoluble powder, the boron nitride (BN). 

85. The elements carbon, boron, and silicon form a natural group, pos- 
sessing many properties in common. They are all capable of existing in 
the amorphous and the crystalline forms ; all incapable of being converted 
into vapour ; all exhibit a want of disposition to dissolve ; all form feeble 
acid oxides by direct union with oxygen ; and all unite with several of 
the metals to form compounds which resemble each other. Boron and 
silicon are capable of direct union with nitrogen, and so is carbon if an 
alkali be present. Recent researches attribute to silicon the power of 
occupying the place of carbon in some organic compounds, and the 
formulae of leucone and silicone (Si 3 H 4 5 and Si 6 H 6 4 ) strongly remind 
us of the organic compounds of carbon with hydrogen and oxygen. In 
many of its physical and chemical characters silicon is closely allied with 
the metals, and it will be found that tin and titanium bear a particular 
resemblance to it in their chemical relations. 

NITROGEN". 

N = 14 parts by weight = l volume ; 14 grains = 467 cub. in. at 60° F. and 30" 
Bar. ; 14 grammes = ll - 2 litres at 0°C. and 760 mm. Bar. 

86. This element, which has already been referred to as forming four- 
fifths of the volume of air, is elsewhere found in nature in the forms of 
saltpetre or potassium nitrate (KN0 3 ), and Chili saltpetre or sodium 

* The author has known them to cut through the bottom of the beaker-glass used in 
separating them from the aluminium. 



NITROGEN. 



123 




nitrate (NaN0 3 ). It also occurs as ammonia (NH 3 ) in the atmosphere 
and in the gaseous emanations from volcanoes. It is contained in the 
greater number of animal, and in many vegetable, substances, and therefore 
has a most important share in the chemical phenomena of life. 

Nitrogen is generally obtained by burning phosphorus in a portion of 
air confined over water (fig. 134). The phosphorus is floated on the water 
in a small porcelain dish, kindled, and covered with a bell-jar. The 
nitrogen remains mixed with clouds of 
phosphoric anhydride ^2^5)5 which ma y 
be removed by allowing the gas to stand 
over water. 

When nitrogen is required in larger 
quantity, it is more conveniently prepared 
by passing air from a gas-holder over 
metallic copper heated to redness in a 
tube. The negative properties of this 
gas, however, are so very uninteresting, 
and render it so useless for most chemical 
purposes, that it will be unnecessary to 
give further details respecting its pre- 
paration. The remarkable chemical in- 
activity of free nitrogen has* been alluded to in the article on atmospheric 
air. It has been seen, however, to be capable of combining directly with 
boron and silicon, and magnesium and titanium unite with it even more 
readily at a high temperature.* It is conspicuous among the elements for 
forming, with hydrogen, a powerful alkali (ammonia, jS t H 3 ), whilst the 
feeble chemical ties which hold it in combination with other elements, 
joined to its character of a permanent gas, render many of its compounds 
very unstable and explosive, as is the case with the so-called chloride and 
iodide of nitrogen, gun-cotton, the fulminates of silver and mercury, nitro- 
glycerine, &c. 

The discovery of nitrogen was made in 1772, by Rutherford (Professor 
of Botany in the University of Edinburgh), who was led to it by the 
observation that respired air was still unfit to support life when all the 
carbonic acid had been absorbed from it by a caustic alkali. Hence the 
name azote (a priv. and £0077, life) formerly bestowed upon this gas. 

Nitrogen has been liquefied by the cold produced by its expansion from 
a compression of 300 atmospheres at 13° C. 



Fig. 134. — Preparation of nitrogen. 



Ammonia. 

NH 3 = 17 parts by weight = 2 volumes. 

87. The proportion of ammonia existing in atmospheric air is so small 
that it is difficult to determine it with precision ; it appears, however, not 
to exceed one-hundredth of a grain in a cubic foot; for although ammonia 
is constantly sent forth into the air by the putrefaction of animal and 
vegetable substances containing nitrogen, it is soon absorbed by water, and 

* Small quantities of ammonia have recently been produced by the combination of 
nitrogen with hydrogen under the influence of electric discharges. G. S. Johnson has 
shown that if any substance capable of absorbing ammonia be present, such as H 2 S0 4 , a 
mixture of N with H 3 may be entirely converted into NH 3 by passing the induced spark 
for some time. 



124 



PREPAKATION OF AMMONIA. 



even by earth and other porous solids. Plants do not appear to be capable 
of absorbing from the atmosphere the nitrogen which it contains so 
abundantly in the un combined form, but to derive their chief supply of 
that element from the ammonia, and nitrates or nitrites contained in the 
air, the soil, and the water. During the life of an animal, it restores to the 
air the nitrogen which formed part of its wasted organs, in part directly 
as ammonia in the breath and in the exhalation from the skin,* whilst 
another portion is separated as urea and uric acid in the urine, to be 
eventually converted into ammonia when the excretion undergoes putrefac- 
tion. Dead animal and vegetable matter, when putref3dng, restores its 
nitrogen to the air, chiefly in the forms of ammonia and substances closely 
allied to it, but partly also, it is said, in the free state. 

The liquor ammonias, or solution of ammonia in water, which is so largely 
used in medicine and the arts, is obtained chiefly from the ammoniacal 
liquor resulting from the destructive distillation of coal for the manufac- 
ture of gas. The ammoniacal liquor of the gas-works contains ammonia 
in combination with carbonic and hydrosulphuric acid. As the first step 
towards extracting the ammonia in a pure state, the liquor is neutralised 
with hydrochloric acid, which combines with the ammonia, expelling the 
carbonic and hydrosulphuric acid gases. Since the latter has a very bad 
smell and is injurious to health, the neutralisation is generally effected 
in covered vats furnished with pipes, which convey 
the gases into a furnace where the hydrosulphuric 
acid is burnt, forming water and sulphurous acid 
gas. The solution is evaporated to expel part of 
the water, and allowed to cool in wooden vessels 
lined with lead, where ammonium chloride is 
deposited in crystals which contain a good deal of 
tarry matter. These crystals are moderately heated 
in an iron pan to deprive them of tar, and are 
finally purified by sublimation, that is, by con- 
verting them into vapour and allowing this vapour 
to condense again into the solid form. For this 
purpose the crystals are heated in a cylindrical 
iron vessel covered with an iron dome lined with 
fireclay. The ammonium chloride rises in vapour 
below a red heat, and condenses upon the dome in 
the form of 'the fibrous cake known in commerce 
of sal ammoniac. 
To obtain ammonia from this salt, an ounce of it is reduced to coarse 
powder, and rapidy mixed with 2 ounces of powdered quicklime. 
The mixture is gently heated in a dry Florence flask (fig. 135), and 
the gas being little more than half as heavy as air (sp. gr. 0*59) may 
be collected in dry bottles by displacement of air, the bottles being 
allowed to rest upon a piece of tin plate which is perforated for the 
passage of the tube. To ascertain when the bottles are filled, a pie'ce of 
red litmus paper may beheld at some little distance above the mouth, 
when it will at once acquire a • blue colour if the ammonia escapes. The 
bottles should be closed with greased stoppers. 




135. — Preparation 
of ammonia. 



* Some doubt exists as to the exhalation of ammonia from the lungs and skin of man 
under normal conditions. 



PROPERTIES OF AMMONIA. 



125 



The action is explained by the following equation :- 



2NH4CI 

Ammonium 
chloride. 



+ CaO = CaCL 



Chloride of 
calcium. 



+ H 2 



+ 2NH ( 



OL 1 




Fig. 136. 



The readiest method of obtaining gaseous ammonia for the study of its properties 
consists in gently heating the strongest liquor ammonia in a retort or flask provided 
with a bent tube for collecting the 
gas by displacement (fig. 136). The 
gas is evolved from the solution at a 
very low temperature, and may be 
collected unaccompanied by steam. 

Ammonia is readily distin- 
guished by its very characteristic 
smell, and its powerful alkaline 
action upon red litmus and tur- 
meric papers. It is absorbed by 
water in greater proportion by 
volume than any other gas, one 
volume of water absorbing more 
than 700 volumes of ammonia 
at the ordinary temperature, and 
becoming 1 \ volumes of solution 
of ammonia. No chemical com- 
bination appears to take place between the water and ammonia, for the 
gas gradually escapes on exposing the solution to the air, and no definite 
compound of the two has been noticed. Moreover, the quantity of 
ammonia retained by the water is dependent upon the temperature and 
pressure, as would be expected if the ammonia were merely dissolved and 
not combined with the water. The escape of the gas from the solution 
is attended with great production of cold, much 
heat becoming latent in the conversion of the 
ammonia from the liquid to the gaseous state. 

The rapid absorption of ammonia by water is well 
shown by filling a globular flask (fig. 137), with the 
gas, placing it with its mouth downwards in a small 
capsule of mercury which is placed in a large basin. If 
this basin be filled with water, it cannot come into 
contact with the ammonia until the mouth of the flask 
is raised out of the mercury, when the water will 
quickly enter and fill the flask. The water should be 
coloured with reddened litmus to exhibit the alkaline 
reaction of the ammonia. 

That the amount of ammonia in solution varies with 
the pressure, may be proved by filling a barometer tube, 
over 30 inches long, with mercury to within an inch of 
the top, filling it up with strong ammonia, closing the mouth of the tube, and 
inverting it with its mouth under mercury ; on removing the finger, the diminished 
pressure caused by the gravitation of the column of mercury in the tube will cause 
the solution of ammonia to boil, from the escape of a large quantity of the gas, which 
will rapidly depress the mercury. If the pressure be now increased by gradually 
depressing the tube in a tall cylinder of mercury (fig. 138), the water will again 
absorb the ammoniacal gas. 

To exhibit the easy expulsion of the ammoniacal gas from water by heat, a 
moderately thick glass tube about 12 inches long and J inch in diameter, may be 
nearly filled with mercury, and then filled up with strong solution of ammonia ; on 
closing it with the thumb, and inverting it into a vessel of mercury (fig. 139) the 
solution will, of course, rise above the mercury to the closed end of the tube. By 
grasping this end of the tube in the hand, a considerable quantity of gas may be 




Fig. 137. 



126 



SPECIFIC GRAVITY OF LIQUIDS DETERMINED. 



expelled, arid the mercury will be depressed. If a little hot water be poured over the 
top of the tube, the latter will become filled with ammoniacal gas, which will be 
absorbed again by the water when the tube is allowed to cool, the mercury returning 
to fill the tube. 

The solution of ammonia, which, is an article of 
commerce, may be prepared by conducting the gas 
into water contained in a two-necked bottle, the 
second neck being connected with a tube passing 
into another bottle containing water, in which any 
escaping ammonia may be condensed. The strength 
of the solution is inferred from its specific gravity, 
which is lower in proportion as the quantity of 
ammonia in the solution is greater. 




A-4 





Fig. 138 Fig. 139. 

Thus, at 57° F., a solution of sp. gr. 0*8844 contains 36 parts by weight of 
ammonia in 100 parts of solution {liquor ammonia? fortissimus) ; the sp. gr. 0*8976 
indicates 30 per cent. ; 0*9106, 25 per cent. ; 0*9251, 20 per cent. ; 0*9414, 15 per 
cent. ; 0*9593, 10 per cent {British Pharmacopoeia); 0*979, 5 per cent. The specific 
gravity is ascertained by comparing the weights of equal volumes of water and of the 
solution at the same temperature. For this purpose a light stop- 
pered bottle is provided, capable of containing about two fluid 
ounces. This is thoroughly dried, and counterposed in a balance 
by placing in the opposite pan a piece of lead, which may be cut 
down to the proper weight. The bottle is then filled with solution 
of ammonia, the temperature observed with a thermometer and 
recorded, the stopper inserted, and the bottle weighed. It is then 
well rinsed out, filled with distilled water, the temperature 
equalised with that of the ammonia by placing the bottle either in 
warm or cold water, and the weight ascertained as before. The 
specific gravity is obtained by dividing the weight of the solution of 
ammonia by that of the water. The ammonia meter (fig. 140) is a 
convenient instrument for rapidly ascertaining the specific gravity 
of liquids lighter than water. It consists of a hollow glass float 
with a long stem, weighted with a bulb containing shot or mercury, 
so that when placed in distilled water it may sink to 1000° of the 
scale marked on the stem, this number representing the specific 
gravity of water. When placed in a liquid lighter than water, it must, of course, 
Sink lower in order to displace more liquid (since solids sink until they have displaced 




Fig. 140, 



LIQUEFACTION OF AMMONIA. 



127 



their own weight of liquid). By trying it in liquids of known specific gravities, the 
mark upon the scale to which it sinks may be made to indicate the specific gravity 
of the liquid. The ammonia meter generally has a scale so divided that it indicates 
at once the percentage weight of ammonia. In this country the specific gravity of 
a liquid is always supposed to be taken at 60° F. 

The common name for solution of ammonia, spirit of harfs horn, is 
derived from the circumstance that it was originally obtained for medicinal 
purposes by distilling shavings of that material. 

When ammonia is exposed to a temperature of — 40° F. (i.e., 72° below 
the freezing-point), or to a pressure of 6J atmospheres at 50°, it con- 
denses to a clear liquid, which solidifies at a temperature of - 103° F. 
to a white crystalline mass. The . comparative ease with which it may 
be liquefied has led to its application in Carre's freezing apparatus (fig. 
141), in which the gas generated by heating a concentrated solution of 
ammonia in a strong iron boiler (A) is liquefied by its own pressure in an 
iron receiver (B) placed in cold water. When the boiler is taken off the 
fire and cooled in water, the liquefied ammonia evaporates very rapidly 
from the receiver back into the boiler, thereby producing so much cold that 
a vessel of water (C) placed in spirit of wine contained in a cavity in the 
receiver, is at once congealed into ice. A refrigerator constructed upon 
this principle is employed in the salt gardens of the south of France, in 
order to render their crystallising operations independent of the temperature 
of the air. 




Fig. 141. — Carre's freezing apparatus. 



Fig. 142. 



The liquefaction of ammonia is very easily effected by heating the ammoniated 
silver chloride in one limb of a sealed tube, the other limb of which is cooled in a 
freezing mixture. A piece of stout light green glass tube (A, fig. 142), about 12 
inches long and ^ inch in diameter, is drawn out, at about an inch from one 
end, to a narrow, neck. About 300 grains of silver chloride (dried at 400° F.) are 
introduced into the tube, so as to lie loosely in it. For this purpose a gutter of stiff 
paper (B) should be cut so as to slide loosely in the tube, the silver chloride 
placed upon it, and when it has been thrust into the tube (held horizontally) the 
latter should be turned upon its axis, so that the silver chloride may fall out of 
the paper, which may be then withdrawn. The tube is now drawn out to a narrow 
neck at about an inch from the other end, as in C, and afterwards carefully bent, as 
in D, care being taken that none of the chloride falls into the short limb of 
the tube, which should be about 4 inches long. The tube is then supported by 
a holder, so that the long limb may be horizontal, and is connected by a tube and 
cork with an apparatus delivering dry ammonia, prepared by heating 1000 grains of 
sal ammoniac with an equal weight of quicklime in a flask, and passing the gas, 



128 



COMBUSTION OF AMMONIA. 



first into an empty bottle (A, fig 143) standing in cold water, and afterwards 
through a bottle (B) filled with lumps of quicklime to absorb all aqueous vapour. 
The long limb of the tube must be surrounded with filtering paper, which is kept 
wet with cold water. The current of ammonia should be continued at a moderate 
rate, until the tube and its contents -no longer increase in weight, which will occupy 
about three hours— about 35 grains of ammonia being absorbed. The longer limb 




Fig. 143. 

is sealed by the blowpipe flame whilst the gas is still passing, and then, as quickly 
as possible, the shorter limb, keeping that part of the tube which is occupied by the 
ammoniated silver chloride still surrounded by wet paper. 

AVhen the shorter limb of this tube is cooled (fig. 144), in a mixture of ice 
and salt (or of 8 ounces of sodium sulphate and 4 measured ounces of common 
hydrochloric acid), whilst the longer limb is gently heated from end to end by waving 
a spirit-flame beneath it, the ammonia evolved by the heat from the ammoniated 
silver chloride, which partly fuses, . will condense into a beautifully clear liquid 
in the cold limb. When this is withdrawn from the freezing mixture, and the tube 
allowed to cool, the liquid ammonia will boil and gradually disappear entirely, the 
gas being again absorbed by the silver chloride, so that the tube is ready to be 
used, again. 





-Liquefaction of ammonia. Fig. 145. 

A small quantity of liquefied ammonia may be more conveniently obtaiued, at 
lecture, by means of a tube prepared as above, but containing about twelve inches of 
fragments of well-dried wood charcoal saturated with dried ammonia gas. The shorter 
limb of the tube should be drawn out to a long narrow point before sealing. This 
limb being immersed in the freezing mixture, the other is placed in a long test-tube 
containing water, which is heated to boiling. The ammonia soon returns to the char- 
coal when the tube cools. 

Ammonia is feebly combustible in atmospheric air, as may be seen by 
holding a taper just within the mouth of an inverted bottle of the gas, 



DECOMPOSITION OF AMMONIA. 



129 



which burns with a peculiar livid flickering light around the flame, but 
will not continue to burn when the flame is removed. During its com- 
bustion the hydrogen is converted into water, and the nitrogen set free. 
In oxygen, however, ammonia burns with a continuous flame. 

This is very well shown by surrounding a tube delivering a stream of ammonia 
(obtained by heating strong solution of ammonia in a retort) with a much wider 
tube open at both ends (fig. 145) 
through which oxygen is passed by 
holding a flexible tube from a gas-bag 
or gas-holder underneath it. On 
kindling the stream of ammonia it 
will give a steady flame of 10 or 12 
inches long. 

A similar experiment may be made 
with a smaller supply of oxygen, by 
lowering the tube delivering ammonia 
into a bottle or jar of oxygen, and 
applying a light to it just as it enters 
the mouth of the jar (fig. 146). 

The elements of ammonia are 
easily separated from each other 
by passing the gas through a red 
hot tube, or still more readily by exposing it to the action of the high 
temperature of the electric spark, when the volume of the gas rapidly 
increases until it is exactly doubled, 2 volumes of ammonia being decom- 
posed into 1 volume of nitrogen and 3 volumes of hydrogen. 

For this experiment, a measured volume of ammonia gas is confined over 
mercury (fig. 147), in a tube through which platinum wires are sealed for the 
passage of the spark from an induction-coil. The volume of the gas is doubled in 






Fig. 147. 

a few minutes, and if the tube be furnished with a stopcock (A), the presence of 
free hydrogen may be shown by filling the open limb with mercury and kindling the 
gas as it issues from the jet.* 

* The eudiometer for passing electric sparks in rapid succession must have the platinum 
wires passed through the glass as shown in fig. 147, or it will be cracked by the heat of the 
sparks. The outlet tube B, closed by a small screw clamp C, pinching a caoutchouc connec- 
tor, allows the mercury to be drawn off when necessary, to equalise the level in the two limbs. 

I 



130 AMALGAM OF AMMONIUM. 

As might be expected from its powerfully alkaline character, ammonia 
exhibits a strong attraction for acids, which it neutralises perfectly. If 
a bottle of ammonia gas, closed with a glass plate, be inverted over a 
similar bottle of hydrochloric acid gas, and the glass plates withdrawn 
(fig 148), the gases will combine, with disengagement of much heat, 
forming a white solid, ammonium chloride (NH 4 C1), in which the acid 
and alkali have neutralised each other. Again, if ammonia be added to 
diluted sulphuric acid, the latter will be entirely neutralised, and by 
evaporating the solution, crystals of ammonium sulphate (NH 4 ) S0 4 
may be obtained. 

The substances thus produced by neutralising the acids with solution 
of ammonia bear a strong resemblance to the salts formed by neutralising 
the same acids with solutions of potash and soda, a circumstance which 
would encourage the idea that the solution of ammonia must contain an 
alkaline hydrate similar to KHO or NaHO. 

Berzelius was the first to make an experiment which appeared strongly 
to favour this view (commonly spoken of as the ammonium theory of 
Berzelius). The negative pole of a galvanic battery was placed in contact 
with mercury at the bottom of a vessel containing a strong solution of 
ammonia, in which the positive pole of the battery was immersed. Oxygen 
was disengaged at this pole, whilst the mercury in contact with the 
negative pole swelled to four or five times its original bulk, and became 
a soft solid mass, still preserving, however, its metallic appearance.* 
So far, the result of the experiment resembles that obtained when 
potassium hydrate is decomposed under similar circumstances, the oxygen 
separating at the positive pole, and the potassium at the negative, 
where it combines with the mercury. Beyond this, however, the 
analogy does not hold ; for in the latter case the metallic potassium can 
be readily separated from the mercury, whilst in the former, all attempts 
to isolate the ammonium have failed, for the soft solid mass resolves 
itself, almost immediately after its preparation, into mercury, ammonia 
(NH 3 ), and hydrogen, one atom of the latter being separated for each 
molecule of ammonia. This would also tend to support the conclusion 
that a substance having the composition NH 3 + H or NH 4 had united 
with the mercury ; and since the latter is not known to unite with any non- 
metallic substance without losing its metallic appearance, it would be fair to 
conclude that the soft solid was really an amalgam of ammonium. How- 
ever, the increase in the weight of the mercury is so slight, and the 
" amalgam," whether obtained by this or by other methods, is so unstable, 
that it would appear safer to attribute the swelling of the mercury to a 
physical change caused by the presence of the ammonia and hydrogen 
gases. It is difficult to believe that the solution of ammonia does really 
contain ammonium hydrate (NH 3 + H 2 = NH 4 HO), when we find it 
evolving ammonia so easily ; but it is equally difficult, upon any other 
hypothesis, to explain the close resemblance between the salts obtained by 
neutralising acids with this solution and those furnished by potash and soda. 

The ordinary mode of exhibiting the production of the so-called amalgam of 
ammonium consists in acting upon the ammonium chloride (NH 4 C1), with sodium 

* This experiment is more conveniently made with a strong solution of ammonium 
sulphate in a common plate. A sheet of platinum connected with the positive pole of the 
battery (five or six Grove's cells) is immersed in the solution, a piece of filter-paper is laid 
upon it, on which is a globule of mercury into which the negative pole is plunged. 



ESTIMATION OF NITROGEN. 131 

amalgam. A little pure mercury is heated in a test-tube, and a pellet of sodium 
thrown into it, when combination takes place with great energy. When the amalgam 
is nearly cool it may be poured into a larger tube containing a moderately strong 
solution of ammonium chloride ; the amalgam at once swells to many times its former 
bulk, forming a soft solid substance lighter than the water, which may be shaken out 
of the tube as a cylindrical mass, decomposing rapidly with effervescence, evolving 
ammonia and hydrogen, and soon recovering its original volume and liquid con- 
dition. 

88. Atomic weight and volume of nitrogen. — Two volumes (one 
molecule) of ammonia, when decomposed by a succession of electric 
sparks, yield a mixture of one volume (one atom) of nitrogen, and three 
volumes (three atoms) of hydrogen. 22*4 litres of ammonia would yield 
11*2 litres of nitrogen, weighing 14 grammes, and, since this is the 
smallest weight of nitrogen which can be found in 22 - 4 litres of any of 
its gaseous compounds, 14 is taken as the atomic weight of nitrogen. 

89. Determination of nitrogen in organic substances. — An exact know- 
ledge of the composition of ammonia is of great importance, because the 
general method of ascertaining the proportion of nitrogen present in animal 
and vegetable substances consists in converting that element into ammonia, 
which, being collected and weighed, furnishes by calculation the weight of 
nitrogen present. 

To ascertain the proportion of nitrogen present in an organic substance, a weighed 
quantity of it is mixed with a large proportion of soda-lime (a mixture of sodium 
hydrate and calcium hydrate), and D c 

introduced into a tube of German , - ,_-=^- ±^^-- ~^ r ^ :r: ^ s =E^°3 

glass (A, fig. 149) to which is Ob^ &==2 4H "'"■' - 
attached, by a perforated cork, a '%^F I l^ ~TT^ 
bulb apparatus (B) containing I l\ 

gen of the substance is evolved in """"^^flKS^S^^^^SlB^ - 

combination with the hydrogen -p. , . n -,_,. ,. c ., 

of the hydrates, in the form of Fl - 149. -Estimation of nitrogen, 

ammonia, which is absorbed by the hydrochloric acid in the bulbs. When the 
whole length of the tube has been heated, the point (C) is nipped off, and air drawn 
through by applying suction to the orifice (D) of the bulb apparatus, so that all the 
ammonia may be carried into the hydrochloric acid. Its weight is then ascertained, 
either_ by evaporating the liquid in a weighed dish placed over a steam bath, and 
weighing the ammonium chloride, or more accurately by converting it into the double 
chloride of platinum and ammonium. Sometimes a solution of sulphuric acid of 
known strength is substituted for the hydrochloric acid in the bulbs, and the weight 
of the ammonia is ascertained by determining the quantity of acid which has been 
neutralised. 

To illustrate the change which takes place when the organic substance is heated 
with the hydrates, let it be supposed that urea is the substance submitted to analysis 
(urea) CH 4 N 2 + 2NaHO = Na 2 C0 3 + 2NH 3 . The caustic soda alone would be too 
fusible, and would corrode the glass too rapidly. 

In the analysis of an organic substance containing carbon, hydrogen, 
nitrogen, and oxygen, the proportions of carbon and hydrogen having been 
ascertained by the method described at p. 84, and that of nitrogen by the 
process given above, the sum of the carbon, hydrogen, and nitrogen is 
deducted from the entire weight of the substance, to obtain the proportion 
of oxygen. The weights thus found are divided by the atomic weights 
of the several elements to obtain the empirical formula, which is converted 
into a rational formula on the principle illustrated at p. 85. 



2-0 - 


- 12 


0-66 - 


- 1 


4-67 - 


- 14 


2-67 - 


- 16 



132 OXIDATION OF AMMONIA. 

For example, 10 grs. of urea were found to contain 2 grs. of carbon, 0'66 
gr. of hydrogen, and 4*67 grs. of nitrogen. 

10 grs. of urea minus 7*33 (carbon, hydrogen, and nitrogen) = 2*67 grs. 
of oxygen. 

Dividing each of these numbers by the atomic weight of the element 
to which it refers, we have — 

0*165 atomic proportion of carbon, 
0*66 „ „ hydrogen, 

0-33 ,, . „ nitrogen, 

0-165 „ „ oxygen, 

leading to the empirical formula, in its simplest form, CH 4 T^ 2 0, for urea. 
But urea is an organic base, capable of uniting with acids to form salts, 
and it is found that to neutralise one molecular weight (36 -5 parts) of 
hydrochloric acid, 60 parts of urea are necessary. This quantity would 
contain 12 parts (one atom) of carbon, 4 parts (four atoms) of hydrogen, 
28 parts (two atoms) of nitrogen, and 16 parts (one atom) of oxygen, so 
that the above formula would correctly represent the molecule of urea. 

90. Formation of ammonia in the rusting of iron. — Although free 
nitrogen and hydrogen can only with difficulty be made to form 
ammonia by direct combination, this compound is produced when the 
nitrogen meets with hydrogen in the nascent state ; that is, at the instant 
of its liberation from a combined form. Thus, if a few iron filings be 
shaken with a little water in a bottle of air, so that they may cling round 
the sides of the bottle, and a piece of red litmus paper be suspended be- 
tween the stopper and the neck, it will be found to have assumed a blue 
colour in the course of a few hours, and ammonia may be distinctly 
detected in the rust which is produced. It appears that the water is 
decomposed by the iron in the presence of the carbonic acid of the air 
and water, and that the hydrogen liberated enters at once into combination 
with the nitrogen, held in solution by the water, to form ammonia. 

If a few inches of magnesium tape be kindled and held over a plate to collect the 
product, it will be found a mixture of MgO and magnesium nitride, which evolves 
NH 3 when boiled with water ; Mg 3 N 2 + 3H 2 = 3MgO + 2NH 3 . 

In his experiments on the electrolysis of distilled water, Davy found that nitric 
acid was formed around the positive pole, by oxidation of the nitrogen of the air con- 
tained in the water, while ammonia was formed at the negative pole by combination 
of the hydrogen with nitrogen. 

91. Production of nitrous and nitric acids from ammonia. — If a few 
drops of a strong solution of ammonia be poured into a pint bottle, and 
ozonised air (from the tube for ozonising by induction, fig. 48) be passed 
into the bottle, thick white clouds will speedily be formed, consisting of 
ammonium nitrite, the nitrous acid having been produced by the oxida- 
tion of the ammonia at the expense of the ozonised oxygen — 

2xh 3 + o 3 = h 2 o + :nh 4 no 2 

Ammonium nitrite. 

If copper filings be shaken with solution of ammonia in a bottle of air, 
white fumes will also be produced, together with a deep blue solution 
containing copper oxide and ammonium nitrite ; the act of oxidation 
of the copper appearing to have induced a simultaneous oxidation of the 
ammonia. 



OXIDATION OF AMMONIA. 



13: 



A coil of thin platinum wire made round a pencil, if heated to redness 
at the lower end and suspended in a flask (fig. 150) with a little strong 
ammonia at the bottom, will continue to glow for a 
great length of time, in consequence of the combina- „J 

tion of the ammonia with the oxygen of the air taking /J~: v i 

place at its surface, attended with great evolution of 
heat. Thick white clouds of ammonium nitrite are 
formed, and frequently red vapour of nitrous anhydride 
(N 2 3 ) itself. A coil of thin copper wire acts in a 




si miliar manner. 

If a tube delivering oxygen gas be passed down to the bottom 
of the flask (fig. 151), the action will be far more energetic, the 
heat of the platinum rising to whiteness, when an explosion 
of the mixture of ammonia and oxygen will ensue. After the 
explosion the action will recommence, so that the explosion will repeat itself as often 
as may be wished. It is unattended with danger if the mouth of the flask be. pretty 
large.* By regulating the stream of oxygen, the bubbles 
of that gas may be made to burn as they pass through the 
ammonia at the bottom of the flask. 

The oxidation of ammonia may also be shown by the 
arrangement represented in fig. 152. Air is slowly passed 
from the gas-bag B, through very weak ammonia in the 
bottle a, into a hard glass tube having a piece of red litmus 
paper at b, and a plug of platinised asbestos in the centre, 
heated by a gas burner ; a piece of blue litmus paper is 
placed at c, and the tube is connected with a large globe (d). 
The red litmus at b is changed to blue by the ammonia, 
whilst the blue litmus at c is reddened by the nitrous acid 
produced in its oxidation, and clouds of ammonium nitrite 
accompanied by red nitrous fumes, appear in d. To obtain 
all the results in perfection, small quantities of ammonia must be successively 
introduced into a. 





Fig. 152. — Oxidation of ammonia. 

(The burner represented in the figure is a Bunsen burner (p. 107), surmounted by a 
T-piece with several holes.) 

When hydrogen or coal gas burns in air, small quantities of nitrous and nitric acids 
are produced, apparently by the oxidation of atmospheric nitrogen. 

In the presence of strong bases, and of porous materials to favour oxi- 
dation, ammonia appears to be capable of suffering further oxidation and 
conversion into nitric acid, which acts upon the base to form a nitrate, 
thus — 

2STH 3 + CaO + 8 = Ca(NCg 2 + 3H 2 . 

Calcium nitrate. 

This formation of nitrates from ammonia is commonly referred to as 
nitrification, and appears to be concerned in the formation of the natural 

* It is advisable to surround the flask with a cylinder of coarse wire gauze. 



134 COMPOUNDS OF NITROGEN AND OXYGEN. 

supplies of saltpetre which are of so great importance to the arts.* Eecent 
investigations indicate that the presence of some minute fungus or 
organised ferment plays an important part in the process. 

This ferment consists of minute round or oval corpuscles, which appear to propagate 
by budding, like yeast. It is abundant in soils, in sewage, and in water contami- 
nated with organic matter. Feeble alkalinity, such as is due to the presence of 
calcium carbonate, is favourable to its action. 

When the nitrification of ammonia takes place in cold dilute solutions, in the dark, 
nitrates only are formed ; but in the case of strong solutions, or at higher tempera- 
tures, or under exposure to light, nitrites are produced. The formation of nitrites or 
nitrates seems to depend, in part, upon the condition of the ferment ; in some cases, 
it produces nitrites only, even if light be excluded. A solution of potassium nitrite 
may be converted into nitrate, in the dark, by adding a little solution in which 
nitrites have lately changed into nitrates, and which therefore contains the nitrifying 
ferment, f 

Compounds op Nitrogen and Oxygen. 

92. Though these elements in their pure state exhibit no attraction for 
each other, five compounds, which contain them in different proportions, 
have been obtained by indirect processes. 

When a succession of strong electric sparks from the induction-coil is 
passed through atmospheric air in a flask (especially if the air be mixed 
with oxygen), a red gas is formed in small quantity, which 
is either nitrous anhydride (N 9 s ) or nitric peroxide 
(N0 2 )4 

If the experiment be made in a graduated eudiometer (fig. 153), 
standing over water coloured with blue litmus, the latter will very 
soon be reddened by the acid formed, and the air will be found to 
diminish very considerably in volume, eventually losing its power 
of supporting combustion, in consequence of the removal of oxygen. 
A U-tube having one limb surmounted by a stoppered globe into 
which platinum wires are sealed, allows the air to be tested with 
a small taper to show that the oxygen has been removed. 

When a few inches of magnesium tape are burnt in a gas-jar of 
Fig. 153. air. red fumes may be perceived on looking down the jar at the 

close of the combustion, and the presence of N 2 3 or N() 2 may be 
shown by drawing the residual air through a mixture of potassium iodide with a 
little starch and acetic acid, when the iodine is set free and blues the starch. This 
renders it probable that the electric spark causes the combination of nitrogen and 
oxygen on account of its high temperature. 

When hydrogen gas, mixed with a small quantity of nitrogen, is 
burnt, the water collected from it is found to have an acid taste and 
reaction, due to the presence of a little nitric acid, resulting from the- 
combination of the nitrogen with the oxygen of the air under the in- 
fluence of the intense heat of the hydrogen flame. 

Since all the compounds of nitrogen and oxygen are obtained, in prac- 
tice, from nitric acid, the chemical history of that substance must precede 
that of the oxides of nitrogen. 

Xitrio Acid. 

93. This most important acid is obtained from saltpetre, which is 
found as an incrustation upon the surface of the soil in hot and dry 

* The charcoal which has been used in the sewer ventilators (see p. 67) has been found 
to contain abundance of nitrates. 

+ Warington on Nitrification, Jour. Chem. Soc, 1879. 

X Brodie has shown that perfectly dry air yields oxides of nitrogen under the influence 
of the induction tube (p. 54). 




PREPARATION OF NITRIC ACID. 



135 



climates, as in some parts of India and Peru. The salt imported into this 
country from Bengal and Oude consists of nitrate of potash or potassium 
nitrate (KN"0 3 ), whilst the 
Peruvian or Chilian saltpetre is 
nitrate of soda or sodium nitrate 
(NaN0 3 ). Either of these will 
serve for the preparation of 
nitric acid. 

On the small scale, in the 
laboratory, nitric acid is pre- 
pared by distilling potassium 
nitrate with an equal weight of 
concentrated sulphuric acid. 




Fig. 154. — Preparation of nit 



acid. 



In order to make the experiment, four ounces of powdered nitre, thoroughly dried, 
may be introduced into a pint stoppered retort (fig. 154) and two and a half mea- 
sured ounces of concentrated sulphuric acid poured upon it. As soon as the acid has 
soaked into the nitre, a gradually increasing heat may be applied by means of an 
Argand burner, when the acid will distil over. It must be preserved in a stoppered 
bottle. 

When the acid has ceased distilling, the retort should be allowed to cool, and filled 
with water. On applying a moderate heat for some time, the saline residue will be 
dissolved. The solution may then be poured into an evaporating dish, and evapo- 
rated down to a small bulk. On allowing the concentrated solution to cool, crystals 
of bisulphate of potash or hydro-potassic sulphate (KHS0 4 ) are deposited, a salt which 
is very useful in many metallurgic and analytical operations. 

The decomposition of potassium nitrate by an equal weight of concen- 
trated sulphuric acid is explained by the equation — 

KN0 3 + H 2 S0 4 = H1S0 3 + KHS0 4 . 

It would appear at first sight that one-half of the sulphuric acid might 
be dispensed with, but it is found that when less sulphuric acid is 
employed, so high a tem- 
perature is required to 
effectthe complete decom- 
position of the saltpetre 
(the above equation then 
representing only the first 
stage of the action), that 
much of the nitric acid is 
decomposed ; and the nor- 
mal potassium sulphate 
(K 2 S0 4 ) which would be 
the final result, is not 
nearly so easily dissolved 
out of the retort by water 
as the bisulphate. 

For the preparation of 
large quantities of nitric 

acid, sodium nitrate is substituted for potassium nitrate, 
cheaper, and furnishing a larger proportion of nitric acid. 

The sodium nitrate is introduced into an iron cylinder (A, fig. 155) lined with fire- 
clay to protect it from the action of the acid, and half its weight of sulphuric acid 
(oil of vitriol) is poured upon it. Heat is then applied by a furnace, into which the 




Fig. 155. — Preparation of nitric acid. 

being much 



136 PROPERTIES OF NITRIC ACID. 

cylinders are built in pairs, when the nitric acid passes off in vapour, and is con- 
densed in a series of stoneware bottles (B), surrounded with cold water. 

2NaN0 3 + H 2 S0 4 = Na 2 S0 4 + 2HN0 3 

Sg£ Oil of vitriol. 5gj™ Nitric acid. 

.The sodium sulphate left in the retort is useful in the manufacture of glass. 

In the preparation of nitric acid, it will be observed at the beginning 
and towards the end of the operation that the retort becomes filled with 
a red vapour. This is due to the decomposition by heat of a portion of the 
colourless vapour of nitric acid, into ^vater, oxygen, and nitric peroxide, — 

2HN0 3 = H 2 + + 2NO a , 
this last forming the red vapour, a portion of which is absorbed by 
the nitric acid, and gives it a yellow colour. The pure nitric acid 
is colourless, but if exposed to sunlight it becomes yellow, a portion 
suffering this decomposition. In consequence of the accumulation of the 
oxygen in the upper part of the bottle, the stopper is often forced out 
suddenly when the bottle is opened, and care must be taken that drops 
of this very corrosive acid be not spirted into the face. 

The strongest nitric acid (obtained by distilling perfectly dry nitre 
with an equal weight of pure oil of vitriol, and collecting the middle 
portion of the acid separately from the first and last portions, which are 
somewhat weaker) emits very thick grey fumes when exposed to damp 
air, because its vapour, though itself transparent, absorbs water very 
readily from the air, and condenses into very minute drops of diluted 
nitric acid which compose the fumes. The weaker acids commonly sold 
in the shops do not fume so strongly. An exact criterion of the strength 
of any sample of the acid is afforded by the specific gravity, which may 
be ascertained by the methods described for ammonia, using a hydrometer 
adapted for liquids heavier than water. Thus, the strongest acid (HN0 3 ) 
has the specific gravity 1*52 ;* whilst the ordinary aquafortis or*diluted 
nitric acid has the sp. gr. 129, and contains only 46*6 per cent, of HN0 3 . 
The concentrated nitric acid usually sold by the operative chemist (double 
aquafortis) has the sp. gr. 1*42, and contains 67*6 per cent, of HN0 3 . 

A very characteristic property of nitric acid is that of staining the skin 
yellow. It produces the same effect upon most animal and vegetable 
matters, especially if they contain nitrogen. The application of this in 
dyeing silk of a fast yellow colour may be seen by dipping a skein of 
white silk in warm diluted nitric acid, and afterwards immersing it in 
dilute ammonia, which will convert the yellow colour into a brilliant 
orange. When sulphuric or hydrochloric acid is spilt upon the clothes, a 
red stain is produced, and a little ammonia restores the original colour ; but 
nitric acid stains are yellow, and ammonia intensifies instead of removing 
them, though it prevents the cloth from being eaten into holes. 

Nitric acid changes most organic colouring matters to yellow, but, unless 
very concentrated, it merely reddens litmus. If solutions of indigo and 
litmus are Warmed in separate flasks, and a little nitric acid added to each, 
the indigo will become yellow and the litmus red. Here the indigo, 
(C 8 H 5 NO) acquires oxygen from the nitric acid, and is convertedinto 
isatine (C 8 H 5 N0 2 ). 

* It is extremely difficult to obtain the HN0 3 free from any extraneous water, as it 
undergoes decomposition not only when vaporised at the boiling-point, but even at ordinary 
temperatures. 



ACTION OF NITRIC ACID UPON METALS. 137 

When nitric acid is heated, it begins to boil at 184° F. (84° C), but it 
cannot be distilled unchanged, for a considerable quantity is decomposed 
into nitric peroxide, oxygen, and water, the two first passing off in 
the gaseous form, whilst the water remains in the retort with the nitric 
acid, which thus becomes gradually more and more diluted, until it con- 
tains 68 per cent, of HN0 3 , when it passes over unchanged at the 
temperature of 248° F. (120° C.). The specific gravity of this acid is 1*42. 
If an acid weaker than this be submitted to distillation, water will pass off 
until acid of this strength is obtained, when it distils over unchanged. 

The specific gravity of the vapour of nitric acid, at 86° C, has been 
determined as 29*6 (H = l), which is sufficiently near to half of 63, to 
show that the molecule HN0 3 would occupy exactly two volumes if it 
had not suffered partial decomposition by heat. 

The facility with which nitric acid parts with a portion of its oxygen, 
renders it very valuable as an oxidising agent. Comparatively few sub- 
stances which are capable of forming compounds with oxygen can escape 
oxidation when treated with nitric acid. 

A small piece of phosphorus dropped into a porcelain dish containing 
the strongest nitric acid (and placed at some distance to avoid danger), 
soon begins to act upon the acid, generally with such violence as to burst 
out into flame, and sometimes to shatter the dish ; the result of this action 
is phosphoric acid, the highest state of oxidation of phosphorus. 

When sulphur is heated with nitric acid, it is actually oxidised to a 
greater extent than when burnt in pure oxygen, for in this case it is con- 
verted into sulphurous acid gas (S0 2 ), whilst nitric acid converts it into 
sulphuric acid H 2 S0 4 . 

Charcoal, which is so unalterable by most chemical agents at the 
ordinary temperature, is oxidised by nitric acid. If the strongest nitric 
acid be poured upon finely powdered charcoal, the latter takes fire at once. 

Even iodine, which is not oxidised by free oxygen, is converted into 
iodic acid (HI0 3 ) by nitric acid. 

But it is especially in the case of metals that the oxidising powers of 
nitric acid are called into useful application. 

If a little black oxide of copper be heated in a test-tube with nitric 
acid, it dissolves, without evolution of gas, yielding a blue solution, which. 
contains copper nitrate — 

2HNO, + CuO = H 2 + Cu(N0 3 ) 2 . 

But when nitric acid is poured upon metallic copper (copper turnings) 
very violent action ensues, red fumes are abundantly evolved, and the 
metal dissolves in the form of copper nitrate, nitric oxide being formed — 
8HN0 3 + Cu 3 = 3Cu(N0 3 ) 2 + 4H 2 + 2NO . 

The nitric oxide itself is colourless, but as soon as it comes into contact 
with the oxygen of the air, it is converted into the red nitric peroxide, 
K"0 + *= N0 2 . 

All the metals in common use are acted upon by nitric acid, except 
gold and platinum, so that this acid is employed to distinguish and 
separate these metals from others of less value. The ordinary ready 
method of ascertaining whether a trinket is made of gold, consists in 
touching it with a glass stopper wetted with nitric acid, which leaves 
gold untouched, but colours base alloys blue, from the formation of 
copper nitrate. The touchstone allows this mode of testing to be 



loS ACTION OF NITRIC ACID ON ORGANIC SUBSTANCES. 

applied with great accuracy. It consists of a species of black basalt', 
obtained chiefly from Silesia. If a piece of gold be drawn across its sur- 
face, a golden streak is left, which is not affected by moistening with 
nitric acid ; whilst the streak left by brass, or any similar base alloy, 
would be rapidly dissolved by the acid. Experience enables an operator 
to determine, by means of the touch-stone, pretty nearly the amount of 
gold present in the alloy, comparison being made with the streaks left 
by alloys of known composition. 

Though all the metals in common use, except gold and platinum, are oxidised by 
nitric acid, they are not all dissolved ; there are two metals, tin and antimony, which 
are left by the acid in the state of insoluble oxides, which possess acid properties, and 
do not unite with the nitric acid. 

If some concentrated nitric acid be poured upon tin filings, no action will be 
observed ; * but on adding a little water, red fumes will be evolved in abundance, 
and the tin will be converted into a white powder, which is tie binoxide of tin or 
stannic oxide (Sn0 2 ), putty powder. 

If the white mixture of stannic oxide with nitric acid be made into a paste with 
slaked lime, the smell of ammonia will be exhaled ; and experiments with other 
metals have shown it to be a general principle, that when any metal capable of 
decomposing water is dissolved in diluted nitric acid, ammonia is always formed, its 
quantity increasing with the degree of dilution of the nitric acid ; of course the 
ammonia combines with the excess of acid present to form ammonium nitrate, and 
the lime was added in the above experiment in order to displace the ammonia from 
its combination, and to exhibit its odour. This conversion of nitric acid into 
ammonia becomes the more interesting when it is remembered that the ammonia 
can be reconverted into nitric acid (p. 132). 

By dissolving zinc in very diluted nitric acid, a very large quantity of ammonia 
may be obtained. The change is easily followed if we suppose the nascent hydrogen, 
produced by the action of the zinc upon the water, to act upon the nitric acid, 
converting its oxygen into water, and its nitrogen into ammonia, thus — HN0 3 + H 8 
= 3H 2 + NH 3 . The exalted attractions possessed by substances in the nascent 
state, that is, at the instant of their passing from a state of combination, are very 
remarkable, and will be found to receive frequent application, t 

Action of nitric acid upon organic substances. — The oxidising action 
of nitric acid upon some organic substances is so powerful as to be 
attended with inflammation; if a little of the 
strongest nitric acid be placed in a porcelain 
capsule, and a few drops of oil of turpentine be 
poured into it from a test-tube fixed to the end 
of a long stick, the turpentine takes fire with 
a sort of explosion. By boiling some of the 
strongest acid in a test-tube (fig. 156), the 
mouth of which is loosely stopped with a plug 
of raw silk or of horse-hair, the latter may be 
made to take fire and burn brilliantly in the 
vapour of nitric acid. 

In many cases the products of the action of 

* It is a fact which has scarcely been explained in a satisfactory manner, that the con- 
centrated nitric acid often refuses to act upon metals which are violently attacked by the 
diluted acid. 

f When a solution of potassium nitrate is mixed with a strong solution of caustic potash, 
and heated with granulated zinc, ammonia is abundantly disengaged, being produced from 
the nitric acid by the nascent hydrogen resulting from the action of the zinc upon the 
caustic potash. 

Recent experiments have indicated the existence of substances intermediate between 
the nitric acid and the ammonia into which it is finally converted. One of these, named 
hydroxylamine, NH 3 0, has been examined. It is a well-defined base, forming crystalline 
salts with the acids. 




ANHYDROUS NITRIC ACID. 139 

nitric acid exhibit a most interesting relation to the substances from 
which they have been produced, one or more atoms of the hydrogen of 
the original compound having been removed in the* form of water by the 
oxygen of the nitric acid, whilst the spaces thus left vacant have been 
filled up by the nitric peroxide resulting from the deoxidation of the nitric 
acid, producing what is termed a nitro-substitution compound. A very 
simple example of this displacement of H by N0 2 is afforded by the 
action of nitric acid upon benzene. A little concentrated nitric acid is 
placed in a flask,. and benzene cautiously dropped into it; a violent action 
ensues, and the acid becomes of a deep red colour ; if the contents of 
the flask be now poured into a large vessel of water, a heavy yellow oily 
liquid is separated, having a powerful odour, like that of bitter almond 
oil. This substance, which is used to a considerable extent in perfumery 
under the name of essence of Mirbane, is called nitro-benzeite, and its 
formula, C 6 H 5 (N0 2 ), at once exhibits its relation to benzene, C 6 H 6 .* 

But the change does not stop here, for by continuing the action of the 
acid, dinitro-benzene C 6 H 4 (X0 2 ) 2 is obtained, in which two atoms of 
hydrogen have been displaced by nitric peroxide. 

It is by an action of this description that nitric acid gives rise to gun- 
cotton, and other explosive substances of the same class, when acting upon 
the different varieties of woody fibre, as cotton, paper, saw-dust, &c. 

The preparation and composition of gun-cotton will be described here- 
after. 

94. The oxidising effects of nitric acid are not confined to the free acid, 
but are shared to some extent by the nitrates. A mixture of nitrate of 
lead with charcoal explodes when sharply struck, from the sudden evolu- 
tion of carbonic acid gas, produced by the oxidation of the carbon. If a 
few crystals of copper nitrate be sprinkled with water and quickly wrapped 
up in tin-foil, the latter will, after a time, be so violently oxidised as to 
emit brilliant sparks. 

But in the case of the nitrates of alkali metals, the oxidation takes 
place only at a high temperature. If a little nitre be fused in an earthen 
crucible or an iron ladle, and, when it is at a red heat, some powdered 
charcoal, and afterwards some flowers of sulphur, be thrown into it, the 
energy of the combustion will testify to the violence of the oxidation. 
In this manner the carbon is converted into potassium carbonate (K 2 C0 3 ), 
and the sulphur into potassium sulphate (K. ? S0 4 ). See Gunpowder. 

95. Anhydrous nitric acid or nitric anhydride (N 2 5 ) is obtained by gently heating 
silver nitrate in a slow cuiTent of chlorine, great care being taken to exclude every 
trace of water ; 2AgX0 3 + Cl 2 = 2AgCl + + X 2 5 . 

It may also be obtained by adding anhydrous phosphoric acid to the strongest 
nitric acid cooled in snow and salt, and carefully distilling at as low a temperature as 
possible into a receiver cooled in snow and salt. 

The anhydride is condensed as a crystalline solid. It forms transparent colourless 
prisms which liquefy at 85° F., and boil at 113°. By a slightly higher temperature 
it is readily decomposed ; and it has been said to decompose even at the ordinary 
temperature, in sealed tubes, which were shattered by the evolved gas. 

When the anhydride is brought in contact with water, much heat is evolved, and 
nitric acid is produced. 

The specific gravity of the vapour of nitric anhydride being unknown, it is only a 
surmise that its molecule is represented by N 2 5 . Its formation by the action of 

* C 6 H 6 + HN0 3 = C 6 H 5 (N0 2 ) + H.,0 
C 6 H e + 2(HXO s ) = C 6 H 4 (N0 2 ) 2 + 2H 2 0. 



140 



NITROUS OXIDE. 



chlorine upon silver nitrate appears to take place in two stages — (1) Ag.N0 2 + Cl 2 
= AgCl + N0 2 C1 (azotyle chloride) + ; and (2) N0 2 C1 + Ag. N0 2 . = AgCl + N0 2 .N0 2 . 
(nitric anhydride). 

The disposition of HN0 3 to give N0 2 as a product of its decomposition, and to 
exchange it for the hydrogen of organic substances, leads to the belief that it is really 

TT \ 

formed upon the type of a molecule of water „ ( 0, in which half the hydrogen 
is displaced by N0 2 . The relation between the anhydride, the acid, and the 
nitrates, would then be a very simple one ; nitric anhydride ^r^-. 2 [ ; nitric 

acid,^ j ; saltpetre, -^-q J 0. 

Nitrates. — Its powerful action on bases places nitric acid among the 
strongest of the acids, though the disposition of its elements to assume the 
gaseous state at high temperatures, conjoined with the feeble attraction 
existing between nitrogen and oxygen, causes its salts to be decomposed, 
without exception, by heat. 

The nature of the decomposition varies with the metal contained in the 
nitrate. The nitrates of alkali metals are first converted into nitrites by 
the action of heat ; thus KN0 3 gives KN0 2 and ; the nitrites them- 
selves being eventually decomposed, evolving nitrogen and oxygen, and 
leaving the oxide of the metal. The nitrates of copper and lead evolve 
nitric peroxide (N0 2 ) and oxygen, the oxides being left. The nitrate of 
mercury leaves red oxide of mercury, which is decomposed at a higher tem- 
perature into mercury and oxygen. 

Nitric acid is a monobasic acid, because it contains only one atom of 
hydrogen to be replaced by a metal. 

Comparatively few of the nitrates are in common use ; the following 
table contains those most frequently used : — 



Chemical Name. 


Common Name. 


Formula. 


Potassium nitrate 
Sodium nitrate 
Strontium nitrate 
Basic bismuth nitrate 
Silver nitrate 


Nitre, saltpetre 
j Cubic nitre ) 
| Peruvian saltpetre \ 

Nitrate of strontian 
j Trisnitrate of bismuth ) 
( Flake white \ 

Lunar caustic 


KN0 3 
NaN0 3 

Sr(N0 3 ) 2 

Bi(N0 3 ) 3 . 2Bi(OH) 3 

AgN0 3 



96. Nitrous oxide or laughing gas (N 2 = 44 parts by weight =2 
volumes) is prepared by heating ammonium nitrate, when it is resolved 
into water and nitrous oxide ; * NH 4 N0 3 = 2H 2 + N 2 0. 

Nitrate of ammonia or ammonium nitrate is obtained by adding fragments of 
ammonium carbonate to nitric acidf diluted with an equal volume of water, until the 
carbonate no longer effervesces in the liquid, which is then evaporated down until a 
drop solidifies on a cold surface, when the whole may be poured out upon a clean 
stone and the mass broken up and preserved in a well -stoppered bottle, because it is 
liable to attract moisture from the air. To obtain the nitrous oxide, an ounce of the 
salt may be gently heated in a small retort, when it melts, boils, and gradually dis- 
appears entirely in the forms of steam and nitrous oxide. The latter may be collected 
with slight loss over water. Crystallised ammonium nitrate may be employed instead 
of the fused salt. 

* By passing the mixture of nitrous oxide and aqueous vapour over hydrate of potash at 
a dull red heat, nitric acid and ammonia are reproduced. 

f Which must remain clear when tested with silver nitrate, showing it to be free from 
chlorine. 



NITRIC OXIDE. 



141 



In the preparation of nitrous oxide, if the temperature be too high, the gas may- 
contain nitric oxide and nitrogen ; NH 4 N0 3 = NO + N + 2H 2 0. To purify the gas, it 
should be passed through a strong solution of ferrous sulphate, to absorb the nitric 
oxide, and afterwards through potash to absorb acid vapours. 

Nitrous oxide is perfectly colourless, but has a slight odour and a 
sweetish taste. Its characteristic anaesthetic property is well known. 
It accelerates the combustion of a taper like oxygen itself, and will 
even kindle into flame a spark at the end of a match. When C is burnt 
into C0 2 by 2N 2 0, it evolves 40,400 more units of heat than when burnt 
in 0, showing that, contrary to the usual law, heat is evolved in the 
decomposition of the N 2 0, amounting to 20,200 units per molecule. 
Nitrous oxide can readily be distinguished from oxygen by shaking it 
with water, which absorbs, at the ordinary temperature, about three- 
fourths of its volume of the nitrous oxide. It is absorbed in larger 
quantity by alcohol. It is also much heavier than oxygen, its specific 
gravity being 1'53, and is liquefied by a pressure of 40 atmospheres at 
45° F., and solidified at - 150° F. It is now sold in a liquid state in 
wrought-iron vessels for use as an anaesthetic in dental surgery. 

The liquid nitrous oxide possesses properties similar to those of liquid carbon 
dioxide with respect to its rapid evaporation ; but it may be drawn into test-tubes in a 
liquid state from the receiver. A lighted match thrown into the liquid burns with 
great brilliancy. When mixed with carbon disulphide and evaporated in vacuo, it 
produces the lowest temperature hitherto obtained - 220° F. 

97. Nitric oxide (NO = 30 parts by weight = 2 volumes) is usually 
obtained by the action of copper upon diluted nitric acid (see page 137). 

300 grains of copper turnings or clippings are introduced into a retort, and 3 
measured ounces of a mixture of concentrated, nitric acid with an equal volume of 
water are poured upon them. A 
very gentle heat may be applied 
to assist the action, and the gas 
may be collected over water (see 
fig. 157), which absorbs the red 
fumes (N0 2 ) formed by the union 
of the NO with the oxygen of the 
air contained in the retort. 

Nitric oxide is distinguish- 
ed from all other gases by the 
production of a red gas, when 
the colourless nitric oxide is 
allowed to come in contact ~ 
with uncombined oxygen, the " 
presence of which, in mixtures 
of gases, may be readily de- 
tected by adding a little nitric oxide. The red gas consists chiefly of 
nitric peroxide (N0 9 ), but it often contains also some (N 2 3 ) nitrous 
anhydride. 

The combination of nitric oxide with oxygen may be exhibited by decanting a pint 
bottle of oxygen, under water, into a tall jar filled with water coloured with blue 
litmus, and adding to it a pint bottle of nitric oxide (fig. 158). Strong red fumes are 
immediately produced, and on gently agitating the cylinder, the fumes are absorbed 
by the water, reddening the litmus. The oxygen will now have been reduced to half 
its volume, and if another pint of nitric oxide be added, the remainder of the oxygen 
will be absorbed, showing that two volumes of nitric oxide combine with one volume of 
oxygen, forming the nitric peroxide which is absorbed by the water. 




142 



PROPERTIES OF NITRIC OXIDE. 



The addition of nitric oxide to atmospheric air was one of the earliest 
methods employed for removing the oxygen in order to determine the 
composition of air; but important variations were observed in the results, 
in consequence of the occasional formation of N 2 3 in addition to the N0 2 . 

The rough analysis of air by this method may be instructively performed with two 
similar gas cylinders, each divided into ten equal volumes. Into one are introduced 
five volumes of air, and into the other five volumes of nitric oxide. On decanting 
the air, under water, into the nitric oxide (fig. 159), the red nitric peroxide will be 
formed and absorbed by the water, the ten volumes of gas shrinking to seven, showing 
that three volumes have been absorbed, of which one volume would of course repre- 
sent the oxygen contained in the five volumes of air. 




Fig. 158. 



Fig. 159. 



The nitric oxide prepared by the action of copper on nitric acid generally contains 
nitrous oxide, and will seldom give correct results in the above experiment. Pure 
nitric oxide may be obtained by heating in a retort 100 grains potassium nitrate, 
1000 grains of ferrous sulphate, and three measured ounces of diluted sulphuric acid 
(containing one measure of acid to three measures of water), which will yield above 
two pints of gas. 

2KN0 3 + 6FeS0 4 + 4H 2 S0 4 = K 2 S0 4 + 3Fe 2 (S0 4 ) 3 + 2NO + 4H 2 . 
In all its properties nitric oxide is very different from nitrous oxide. 
It is much lighter, having almost exactly the same specific gravity as air, 
viz., 1 "04, and is not dissolved to an important extent by water. It is more 
difficult to liquefy, requiring a pressure of 104 atmospheres at - 11° C. 
When a lighted taper is immersed in nitric oxide it is extinguished, 
although this gas contains twice as much oxygen as nitrous oxide, which 
so much accelerates the combustion of a taper ; for the elements are held 
together by a stronger attraction in the nitric oxide, so that its oxygen is 
not so readily available for the support of combustion. (The nitric oxide 
prepared from copper and nitric acid sometimes contains so much nitrous 
oxide that a taper burns in it brilliantly.) Even phosphorus, when just 
kindled, is extinguished in nitric oxide, but when allowed to attain to full 
combustion in air, it burns with extreme brilliancy in" the gas. Indeed, 
nitric oxide appears to be the least easy of decomposition of the whole 
series of oxides of nitrogen, which accounts for it being the most common 
result of the decomposition- of the other oxides. Nitrous oxide itself, 
when passed through a red hot tube, is partly converted into nitric oxide ; 
and when a taper burns in a bottle of nitrous oxide, the upper part of the 
bottle is often filled with a red gas, indicating the formation of nitric oxide, 
and its oxidation by the air entering the bottle. 



NITROUS ANHYDRIDE. 



143 




^L.Q^' 



Fig. 160. 



The difference in the stability of the two gases is also shown by their 
behaviour with hydrogen. A mixture of nitrous oxide with an equal 
volume of hydrogen explodes 
when in contact with flame, yield- 
ing steam and nitrogen, but a 
mixture of equal volume of nitric 
oxide and hydrogen burns quietly 
in air, the hydrogen not decom- 
posing the nitric oxide. An ex- 
cess of hydrogen, however, is 
capable of decomposing nitric 
oxide, ammonia and water being 
formed. 

If two volumes of nitric oxide be 
mixed with five volumes of hydrogen 
and the gas passed through a tube 
having a bulb filled with platinised 
asbestos (fig. 160),*' the mixture issuing 

from the orifice of the tube will produce the red vapours by contact with the air, 
which will strongly redden blue litmus ; but if the platinised asbestos be heated 
with a spirit-lamp, the hydrogen, encouraged by the action of the platinum (91) will 
decompose the nitric oxide, and strongly alkaline vapours of ammonia will be produced, 
restoring the blue colour to the reddened litmus; NO + H 5 = NH 3 + H 2 0. It will 
be remembered that when oxygen is in excess, ammonia is converted, under the 
influence of platinum, into water and nitrous acid (91). 

Nitric oxide is readily absorbed by ferrous salts (salts of protoxide of 
iron) with which it forms dark brown solutions. If a little solution of 
ferrous sulphate (FeS0 4 ) be shaken in a cylinder of nitric oxide closed 
with a glass plate, the gas will be immediately absorbed and the solution 
will become dark brown. On applying heat, the brown compound is 
decomposed. A compound of 4FeS0 4 and NO has been obtained in small 
brown crystals, which lose all their nitric oxide in vacuo. 

98. Nitrous anhydride (N 2 3 = 76 parts by weight). — Ammonium 
nitrite is said to exist in minute quantity in rain water, and nitrites are 
occasionally found in well-waters, where they have probably been formed 
by th,e oxidation of ammonia (91). Small quantities of ammonium nitrite 
appear to be formed by the combustion in air of gases containing hydro- 
gen, this element uniting with the atmospheric oxygen and nitrogen. 

Nitrous anhydride may be obtained by heating starch with nitric acid, 
but the most convenient process consists in gently heating nitric acid (sp. 
gr. 1-35) with an equal weight of white arsenic, and passing the gas, first 
through a U-tube (fig. 161) surrounded with cold water, to condense uu- 
decomposed nitric acid, then through a similar tube containing calcium 
chloride, to absorb aqueous vapour, and afterwards into a U-tube sur- 
rounded with a freezing mixture of ice and salt. Through a small tube 
opening into the bend of this U-tube, the condensed nitrous anhydride 
drops into a tube drawn out to a narrow neck, so that it may be drawn off, 
and sealed by the blowpipe — 

2HN0 3 + As 2 3 + 2H 2 = 2H 3 As0 4 + N 2 3 



White arsenic. 



Arsenic acid. 



* Asbestos which has been wetted with solution of platinic chloride, dried, and heated 
to redness, to reduce the platinum to the metallic state. 



144 



NITROUS ANHYDRIDE. 



Tilden prepares nitrous anhydride by decomposing the acid nitrosyle 
sulphate (see Aqua Regia) with a small quantity of water — 
2NOHS0 4 + H 2 = 2H 2 S0 4 + N 2 3 . 
Mtrous anhydride is a blue liquid which boils below 32° ¥., becoming 
converted into a red vapour, and partly decomposed into NO and N0 2 . 
Water at about 32° F. dissolves the acid without decomposing it, yielding 
a blue solution, which is decomposed, as the temperature rises, into nitric 
acid, which remains in the liquid, and nitric oxide which escapes with 
effervescence, 3N 2 3 + H 2 = 2HN0 3 + 4TO . 

The blue solution is believed 'to contain nitrous acid, HN0 2 , resulting 
from the reaction N 2 3 + H 2 = 2HN0 2 ; but this compound has not 
been obtained in a pure state. 

A very dilute solution of nitrous acid may be preserved for some time 
and even distilled without decomposition. 




Fig. 161. — Preparation of nitrous anhydride. 

The salts of nitrous acid, or nitrites, are interesting on account of their 
production from the nitrates by the action of heat (p. 140). 

If potassium nitrate be fused in a fireclay crucible and heated to redness, it will 
evolve bubbles of oxygen, and slowly become converted into potassium nitrite 
(KN0. 2 ). The heat may be continued until a portion removed on the end of an 
iron rod, and dissolved in water, gives a strongly alkaline solution. The fused mass 
may then be poured upon a dry stone, and when cool, broken into fragments and 
preserved in a stoppered bottle. On heating a fragment of the nitrite with diluted 
sulphuric acid, red vapours will be disengaged, but these contain little nitrous acid,- 
the greater part of this being decomposed by the water into nitric acid and nitric 
oxide. 

When nitrous acid acts upon ammonia, both compounds suffer decomposition, 
water and nitrogen being the results ; NH 3 + HN0 2 = N 2 + 2H 2 0. 

This is sometimes taken advantage of in preparing nitrogen gas by boiling mixed 
solutions of sal ammoniac and potassium nitrite ; NH 4 C1 + KN0 2 = KC1 + 2H 2 + N. 2 . 

In experiments upon organic compounds, nitrous acid is sometimes employed as a 
convenient agent for effecting simultaneously the removal of 3 atoms of hydrogen 
from a compound, and the insertion of 1 atom of nitrogen. 

When solutions of nitrites are heated in contact with air, they gradually absorb 
oxygen, becoming converted into nitrates. 

When a solution of sodium nitrate, NaN0 3 , is acted on by sodium amalgam, it is 
first reduced to sodium nitrite, NaN0 2 , and then to sodiitm hyponitrite, NaNO, which 
gives a yellow precipitate of silver hyponitrite, AgNO, on addition of silver nitrate 
to the solution after neutralisation with nitric acid. The sodium salt may be pre- 
pared in large quantity by fusing sodium nitrate with iron filings in an iron crucible, 

By boiling 



PROPERTIES OF NITRIC PEROXIDE. 14 

the fused mass with water, filtering, and evaporating to a small bulk, needle-shaped 
crystals are obtained on cooling, which have the formula KaN0.3Aq. 

The corresponding acid, HNO, has not been obtained, the attempts to prepare it 
having resulted in the formation of nitrous oxide and water ; 2HNO = N 2 + H20- 

99. Nitric peroxide (N0 2 = 46 parts by weight = 2 volumes), also 
called hyponitric acid and peroxide of nitrogen or pemitric oxide : for- 
merly known as nitrous acid. — By passing a mixture of nitric oxide with 
half its volume of oxygen, free from every trace of moisture, into a per- 
fectly dry tube cooled in a mixture of ice and salt, the dark red gas is 
condensed into colourless prismatic crystals which melt at 10° F. into 
a nearly colourless liquid. This gradually becomes yellow as the tempera- 
ture rises, and at the ordinary temperature has a deep orange colour. 
It is very volatile, boiling at 71° IT., and being converted into a red- 
brown vapour, which was long mistaken for a permanent gas, on account 
of the great difficulty of condensing it when once mixed with air or 
oxygen. Nitric peroxide is also obtained mixed with one-fourth of its 
volume of oxygen, by heating lead nitrate (fig. 162) ; 
Pb(]N T 03) 2 = PbO + 2N0 2 + . 

The vapour of nitric peroxide is much heavier 
than atmospheric air. 




Its specific gravity (compared with hydrogen at the same 
temperature) diminishes as the temperature rises. At 275° 
F. it is 23 times as heavy as hydrogen, showing its mole- 
cular weight to be 46. This variation in density, in con- 
junction with the other changes, with increase of tempera- 
ture, lead to the belief that the molecule of nitric peroxide 
at low temperatures (in its liquid state) is N 2 4 , and becomes * ig. lb A —Preparation 
decomposed into 2N0 2 at high temperatures. ot nitric P er0X1( l e - 

Its colour varies with the temperature, becoming very dark at 100° F. 
The smell of the vapour is very characteristic. It supports the 
combustion of strongly burning charcoal or phosphorus, and oxidises 
most of the metals, potassium taking fire in it spontaneously. The 
nitric peroxide must, therefore, rank as a powerful oxidising agent, 
and it is the presence of this substance in the red fuming nitric acid 
that imparts to it higher oxidising powers than those of the colourless 
nitric acid. 

The so-called nitrous acid of commerce is really nitric acid holding in 
solution a large proportion of nitric peroxide, and is prepared by intro- 
ducing sulphur into the retorts containing the mixture of sodium nitrate 
and sulphuric acid employed in the preparation of the nitric acid, a por- 
tion of which is deoxidised and converted into nitric peroxide. "Water 
in excess immediately decomposes the nitric peroxide into nitrous acid 
and nitric acid ; 2N0 2 + H 2 = HN0 3 + HN0 2 . 

When water is gradually added to liquid nitric peroxide, it effervesces, 
from escape of nitric oxide, and becomes green, blue, and ultimately 
colourless ;' 3N0 2 + H 2 = NO + 2HX0 3 . If the red nitric acid of com- 
merce be gradually diluted with water, it will be found to undergo 
similar changes, always becoming colourless at last. The nitric acid 
which has been used in a Grove's battery always has a green colour, 
from the large amount of nitric peroxide which has accumulated in it, in 
consequence of the decomposition of the acid by the hydrogen disengaged 
during the action of the battery; H + HM) 3 = H 2 + N0 2 . If this 
green acid be diluted with a little water it becomes blue, and a larger 

K 



146 GENERAL SUMMARY OE OXIDES OF NITROGEN. 

quantity of water renders it colourless, causing the evolution of nitric 
oxide. Similar colours are obtained by passing nitric oxide into nitric 
acid of different degrees of concentration, apparently because nitric 
peroxide is formed and dissolved by the acid. 

When silver, mercury, and some other metals are dissolved in cold nitric 
acid, a green or blue colour is often produced, leading a novice to suspect 
the presence of copper, the colour being really caused by the solution, in 
the unaltered nitric acid, of the nitric peroxide produced by the deoxida- 
tion of another portion. 

Nitric peroxide was formerly believed to be an independent acid 
capable of forming salts. It is true that its vapours have a strongly acid 
reaction to test-papers, but when brought into contact with alkalies, it pro- 
duces a mixture of nitrate and nitrite — 

2NO a + 2KHO = KN0 3 + KN0 2 + H 2 . 

100. General review of the oxides of nitrogen. — Nitric oxide, nitrous 
acid, and nitric peroxide, are very remarkable for their relations to 
oxygen. Nitric oxide is one of the very few substances which combine 
with dry oxygen at the ordinary temperature, aud yet the nitric peroxide 
which is thus produced is very ready to yield its oxygen to other sub- 
stances. Nitrous acid, as might be expected, is intermediate in this 
respect, being capable of acting as a reducing agent upon powerfully 
oxidising substances, and as an oxidising agent upon substances having 
a great attraction for oxygen. Thus a solution of potassium nitrite 
acidified with sulphuric acid will bleach potassium permanganate, reducing 
the permanganic acid tomanganous oxide (MnO); whilst if added to ferrous 
sulphate, the nitrite converts the ferrous into ferric salt, and this solution, 
which was capable of reducing the potassium permanganate before, is now 
found to be without effect upon it, unless an excess of the nitrite has 
been added. 

The oxides of nitrogen, as illustrating combination in multiple propor- 
tions by weight and volume.- — In its most general form, the Law of Multiple 
Proportions may be thus stated. When a substance (A) combines with 
another substance (B) in more than one proportion, the quantities of B 
which combine with a constant quantity of A, are multiples of the 
smallest combining quantity of B by some whole number. 

In the oxides of nitrogen this law is exemplified, in the simplest form, 
since the quantities of oxygen which combine with a constant quantity of 
nitrogen are multiples of the least combining quantity of oxygen by 2", 
3, 4, and 5. 







" N 





Nitrous oxide, . 


. N 2 


28 


16 


Nitric oxide (two molecules), 


• N a o a 


28 


16 x 2 


Nitrous anhydride. 


. N.,0 3 


28 


16 x 3 


Nitric peroxide, . 


. na 


28 


16 x 4 


Nitric anhydride, 


. na 


• 28 


16 x 5 



It was shown at p. 131 that there is ground for representing the atomic weight of 
nitrogen as = 14. 

When nitrous oxide is passed through a red hot porcelain tube, its volume is 
increased by one-half, and the resulting gas is found to be a mixture of 1 volume 
of oxygen and 2 volumes of nitrogen. Hence it is inferred that, in nitrous oxide, 
2 volumes or atoms (28 parts) of nitrogen are united with 1 volume or atom (16 parts) 
of oxygen, to form 2 volumes or one molecule of nitrous oxide (representing 44 parts 
by weight). 



CHLORINE. . 147 

When charcoal is strongly heated in nitric oxide, the volume of the gas remains 
unchanged ; but it is found on analysis to have become converted into a mixture 
of equal volumes of carbonic acid gas and nitrogen (2N0 + C = C0 2 + N 2 ). Since 
1 volume of carbonic acid gas contains 1 volume of oxygen (page 91), the experiment 
proves that 1 volume of oxygen and 1 volume of nitrogen exist in 2 volumes of 
nitric oxide, or that 1 atom of nitrogen (or 14 parts) is combined with 1 atom of 
oxygen (16 parts) in 2 volumes (one molecule, or 30 parts by weight) of nitric oxide. 

The direct evidence of the composition of nitrous anhydride is not so satisfactory 
as that in the two preceding cases. This gas has been obtained, however, by the 
direct union of 1 volume of oxygen with 4 volumes of nitric oxide, leading to the 
conclusion that it contains N 2 3 . 

Nitric peroxide has been analysed by passing the vapour produced from a known 
weight of the liquid, over red hot metallic copper, which absorbed the oxygen, leaving 
the nitrogen to be collected and measured. It was thus found that 14 parts by weight 
(one atom =1 volume) of nitrogen were combined with 32 parts by weight (two 
atoms = 2 volumes) of oxygen, a result which is confirmed by the direct union of 2 
volumes of NO (one molecule) with 1 volume of oxygen (one atom.) to form N0 2 . 

Nitric anhydride, or anhydrous nitric acid, was analysed by a method similar to 
that employed for nitric peroxide, and was found to contain 28 parts by weight 
(2 atoms) of nitrogen, combined with 80 parts (5 atoms) of oxygen. The volume 
occupied by the molecule of nitric anhydride in the state of vapour has not been 
determined, on account of the want of stability of this compound. 

The facility with which nitrous anhydride and nitric peroxide can be decomposed with 
formation of nitric oxide, renders it probable that they really contain that compound. 
To express this, they may plausibly be represented as formed after the same plan as a 

TT \ 

molecule of water. Just as in „ ( 0, the two atoms of hydrogen are linked together 

by the diatomic oxygen, so in nitrous anhydride, ^q I 0, two molecules of nitric 
oxide are linked together by the atom of oxygen, whilst in nitric peroxide (N 2 4 ) a 
molecule of NO is bound up with a molecule of N0 2 thus ^-r^ [ 0. If nitric 

anhydride be represented by -^ 2 | 0, it is easy to understand the behaviour of 

these three oxides with the alkalies. Thus, by the action of nitrous anhydride on 

caustic potash, we obtain potassium nitrite -»™ [ 0, whilst nitric acid gives potassium 

K ) 
nitrate, -^ > 0, and nitric peroxide gives a mixture of both salts. 

From the experiments of Berthelot, it appears that the decomposition of all the 
oxides of nitrogen is attended by evolution of heat, which is greatest for nitric oxide. 

CHLOKIKE. 

CI = 35 -5 parts by weight = 1 volume ; 35'5grs. =46 7 cub. in. at 60° F. and 30" Bar. ; 
35*5 grammes = 11 "2 litres at 0° C. and 760 mm. Bar. 

101. This element is never fonnd in the uncombined state, but is very 
abundant in the mineral world in the forms of sodium chloride (common 
salt) and potassium chloride. In these forms also it is an important con- 
stituent of the fluids of the animal body, but as it is not found in sufficient 
proportion in vegetable food, or in the solid parts of animal food, a 
quantity of salt must be added to these in order to form a wholesome 
diet. Sodium chloride is indispensable as a raw material for several of 
the most useful arts, such as the manufactures of soap and glass, bleaching, 
&c. ; in fact, it is the source of three of the most generally useful chemical 
products, viz., chlorine, hydrochloric acid, and soda. 

About the middle of the 17th century, a German chemist named 
Glauber distilled some common salt with sulphuric acid, and obtained a 
strongly acid liquid to which he gave the name muriatic acid (from muria, 
brine), and which was proved to be identical with the acid long known to 



148 



PREPARATION OE CHLORINE. 



the alchemists as spirit of salt. The saline mass which was left after the 
experiment was then termed Glauber's salt, hut afterwards received its 
present name of sodium sulphate. 

It was undoubtedly a natural inference from this experiment that com- 
mon salt was composed of muriatic acid and soda, and that the sulphuric 
acid had a greater attraction for the soda than the muriatic acid, which 
was therefore displaced by it. In accordance with this view, common 
salt was called muriate of soda, without further question, until the year 
1810, when the experiments of Davy proved that it was really composed 
of the two elementary substances, chlorine and sodium, and must there- 
fore be styled, as it now is, sodium chloride, and represented by the 
formula NaCl. It was further shown by Davy that the muriatic acid 
was really composed of chlorine and hydrogen, and that it was, in fact 
(HC1), chloride of sodium (NaCl), in which the sodium had been dis- 
placed by hydrogen. 

Preparation of chlorine. — In order to extract chlorine from common 
salt, it is heated with black oxide of manganese and diluted sulphuric 
acid, when the sulphates of sodium and manganese are left in solution, 
and chlorine escapes in the form of gas — 

2NaCl + Mn0 2 + 2H 2 S0 4 - Na 2 S0 4 + MnS0 4 + 2H 2 + Cl 2 . 

600 grains of common salt may be mixed with 450 grains of binoxide of manganese, 
introduced into a retort (fig. 163), and a cold mixture of 1£ oz. by measure of strong 
sulphuric acid with 4 oz. of water poured upon it. The retort having been well 




Fig. 163.— Preparation of chlorine. 

shaken, to wet the powder thoroughly with the acid, a very gentle heat is applied, 
and the gas collected in bottles filled with water and inverted in the pneumatic 
trough. When the bottles are filled, the stoppers, previously greased, must be 
inserted into them under water. The first bottle or two will contain the air from the 
retort, and will therefore have a paler colour than the pure chlorine afterwards col- 
lected. It is advisable to keep a jar filled with water standing ready on the shelf of 
the trough, so that any excess of chlorine may be passed into it instead of being 
allowed to escape into the air, causing serious inconvenience. The bottles of moist 
chlorine must always be preserved in the dark. Chlorine may also be conveniently 
prepared by gently heating 500 grains of binoxide of manganese with 4 oz. (measured) 
of common hydrochloric acid — 

Mn0 2 + 4HC1 = MnCl 2 + 2H 2 + Cl 2 . 
Either of the above methods will furnish about five pints of chlorine, 
as a carrier ofs process for the manufacture of chlorine, the manganese is made to act 
as a carrier of oxygen from the atmosphere to the hydrogen of the hydrochloric acid, 




LIQUEFACTION OF CHLORINE. 149 

setting the chlorine free. For this purpose the chloride of manganese obtained in 
the above process is decomposed by lime; MnCl 2 + CaO = CaCl 2 + MnO. By mixing 
the MnO with more lime, and blowing atmospheric air through the mixture, Mn0 2 
is reproduced, and may be employed for decomposing a fresh quantity of HC1. In 
Deacons process, a mixture of air and hydrochloric acid gas is passed over heated 
fire-brick which has been soaked in solution of copper sulphate and. sodium sulphate, 
and dried. The final result is expressed by the equation 2HC1 + (N 4 + 0) = H 2 + C1 2 
+ N 4 , so that the chlorine obtained is mixed with twice its volume of nitrogen, 
which is stated, however, not to interfere seriously with its useful application. The 
action of the copper-salt has not been clearly explained, but it appears to depend upon 
the instability of the chlorides of copper under the influence of heat and oxygen. 

Properties of chlorine. — The physical and chemical properties of chlorine 
are more striking than those of any element hitherto considered. Its 
colour whence it derives it name (xAwpos, pale green), is bright greenish- 
yellow, its odour insupportable. It is twice and a half as heavy as air 
(sp. gr. 2 "47), and may be reduced to the liquid state by a pressure of only 
four atmospheres at 60° F. If a bottle of chlorine be 
held mouth downwards in water, its stopper removed, 
one-third of the chlorine decanted into a jar, and the 
rest of the gas shaken with the water in the bottle, 
the mouth of which is closed by the palm of the hand 
(fig. 164), the water will absorb nearly twice its 
volume of chlorine, producing a vacuum in the bottle, 
which will be held firmly against the hand by atmo- 
spheric pressure. If air be then allowed to enter, and 
the bottle again shaken as long as any absorption 
takes place, a saturated solution of chlorine (liquor chlori, chlorine water) 
will be obtained. By exposing this yellow solution to a temperature 
approaching 32° F., yellow crystals of hydrate of chlorine (C1.5H 2 0) are 
obtained, the liquid becoming colourless. 

When the water in the pneumatic trough, over which chlorine is being collected, 
happens to be very cold, the gas is often so foggy as to be quite opaque, in conse- 
quence of the deposition of minute crystals of the hydrate. On standing, the gas 
becomes clear, crystals of the hydrate being deposited like hoar-frost upon the sides 
of the bottle ; the gas also becomes clear when the bottles are slightly warmed. 

The hydrate of chlorine affords a convenient source of liquid chlorine. A number 
of bottles of saturated solution of chlorine, prepared as above, are exposed on a cold 
winter's day until the hydrate has crystallised. The crystals are thrown upon a 
filter cooled to nearly 32°, allowed to drain, and rammed into a pretty strong tube 
closed at one end, about 12 inches long, and ^ an inch in diameter, previously 
cooled in ice or snow. The tube having been nearly filled with the crystals, is kept 
surrounded with snoAV, whilst its upper end is gradually softened in the blowpipe 
flame and drawn off so as to be strongly sealed. When this tube is immersed in 
water at 100° F., the chlorine separates from the water, and two layers of liquid are 
formed, the lower one consisting of amber-yellow liquid chlorine (sp. gr. 1 *33), and 
the upper, about three times its volume, of a pale yellow aqueous solution of chlorine. 
On allowing the tube to cool again, the crystalline hydrate is reproduced, even at 
common temperatures, being more permanent under pressure. It may even be sub- 
limed in a sealed tube. 

Liquid chlorine may also be obtained in a state in which it can be preserved, by 
disengaging the chlorine in a sealed tube. (as in the liquefaction of ammonia) from 
about 200 grains of platinic chloride previously dried, at 400° F. The chloride 
is heated with a spirit-lamp in one limb of the tube, whilst the other is immersed 
in a freezing mixture. The face and hands of the operator should be protected 
against the bursting of the tube. 

The most characteristic chemical feature of chlorine is its powerful 
attraction for many other elements at the ordinary temperature. Among 
the non-metals, hydrogen, bromine, iodine, sulphur, selenium, phosphorus, 



150 



EXPERIMENTS WITH CHLOKINE: 



and arsenic, combine spontaneously with chlorine, and nearly all the 
metals behave in the same way. 

If a piece of dry phosphorus be placed in a deflagrating spoon, and immersed in a 
bottle of chlorine (fig. 165), it will take fire spontaneously, combining with the chlorine 

to form phosphorous' chloride (PC1 3 ). A tall glass 
shade may be placed over the bottle, which should 
stand in a. plate containing water, so that the 
fumes may not escape into the air. 

If phosphorus be placed in a bottle of oxygen to 
which a small quantity of chlorine has been added, 
it will burst out after a minute or two into most 
brilliant combustion. 

Powdered antimony (the metal, not the sulphide), 
sprinkled into a bottle of chlorine (fig. 166), de- 
scends in a brilliant shower of white sparks, the 
antimony burning in the chlorine to form anti- 
monious chloride (SbCl 3 ). A little water should 
be placed at the bottom of the bottle to prevent 
it from being cracked, and the fumes should be 
restrained by a shade standing in water. 
If a flask, provided with a stopcock (fig. 167), be filled with leaves of Dutch metal 
(an alloy of copper and zinc resembling gold leaf), exhausted of air, and screwed on 
to a capped jar of chlorine standing over water, it will be found, on opening the 




Pig. 165. 





Fig. 166. 



Pig, 167. 



stopcocks so that the chlorine may enter the flask, that the metal burns with a red 
light, forming thick yellow fumes containing cupric chloride (CuCl 2 ) and zinc chloride 
(ZnCl 2 ). If a gold leaf be suspended in chlorine, it will not be immediately attacked, 
but will gradually become converted into auric chloride (AuCl 3 ). 

102. The most important useful applications of chlorine depend upon 
its powerful chemical attraction for hydrogen. The two gases may be 
mixed without combining, if kept in the dark ; but when the mixture is 
exposed to light, they combine to form hydrochloric acid gas (HC1), with 
a rapidity proportionate to the intensity of the actinic rays (or rays capable 
of inducing chemical change) in the light employed. Exposed to gas-light 
or ordinary diffused daylight, the hydrogen and chlorine combine slowly ; 
but direct sunlight causes sudden combination, attended with explosion, 
resulting from the expansion which the hydrochloric acid formed suffers 
by the heat evolved in the act of combination. The light of magnesium 
burning in air, and some other artificial lights, also cause sudden com- 
bination. 



SYNTHESIS OF HYDROCHLORIC ACID. 



151 



Two pint gas-bottles should be ground so that their mouths may be fitted accu- 
rately to each other, and filled respectively with dry hydrogen and dry chlorine, both 
gases having been dried by passing through oil of vitriol, and collected, the hydrogen 
by upward, and the chlorine by downward, displacement of air. The mouths should 
be slightly greased before the bottles are filled with gas, and afterwards closed with 
glass plates. On placing the bottles together, and removing the plates so that the 
gases may come in contact (see fig. 148), the yellow colour of the chlorine will be 
permanent as long as the mixture is kept in the dark, but on exposure to daylight 
the colour will gradually disappear, the hydrochloric acid gas being colourless. If 
the bottles be now closed with glass plates, the small quantity of gas which escapes 
during the operation will be seen to fume strongly in air, a property not possessed 
either by hydrogen or chlorine ; and when the necks of the bottles are immersed in 
water, and the glass plates withdrawn, the water will gradually absorb the gas, and be 
forced into the bottles so as to fill them, with the exception of a small space occupied 
by the air accidentally admitted, showing that the hydrochloric acid gas possesses 
the joint volumes of the hydrogen and chlorine. If the water be tinged with blue 
litmus, it will be strongly reddened as it enters the bottles. 

The sudden union of the gases with explosion may be safely exhibited in a Flor- 
ence flask. The flask is filled with water, which is then poured out into a measure. 
Exactly half the water is returned 
to the flask, and its level in the 
latter carefully marked with a dia- 
mond or file. The flask having been 
again filled with water, is closed with 
the thumb and inverted in the pneu- 
matic trough, so that hydrogen may 
be passed up into it to displace one- 
half of the water. A short-necked 
funnel is then inserted, under the 
water, into the neck of the flask, 
and chlorine rapidly decanted up 
from a gas-bottle (fig. 168) until the 
rest of the water has been displaced. 
The flask is now raised from the 
water and quickly closed with a cork 
(fig. 169), through which pass two 
gutta-percha-covered copper wires, 

the ends of which have been stripped and brought sufficiently near to each other 
to allow of the passage of the electric spark within the flask. The ends external to 
the flask are also stripped and 
bent into hooks, for convenient 
connexion with the conducting 
wires. The flask is placed upon 
the ground, and covered with a 
wooden box to prevent the pieces 
from flying about. On connecting 
the copper wires with the con- 
ducting wires from an induction- 
coil or on electrical machine, it 
will be heard, on passing the spark, 
that the mixture has violently ex- 
ploded ; on raising the box, it will 
be found filled with strong fumes 
of hydrochloric acid, and a heap of 
small fragments of glass will repre- 
sent the flask. 

A flask filled in the same way with the mixture of hydrogen and chlorine may be 
attached to the end of a long stick, and thrust out into the sunlight, when it explodes 
with great violence. 

To illustrate the direct combination of hydrogen and chlorine under the influence 
of artificial light, it is better to employ the mixture of exactly equal volumes of the 
two gases obtained by decomposing hydrochloric acid by the galvanic current. The 
voltameter (A, fig. 170) is filled with concentrated hydrochloric acid, and its con- 
ducting wires (B) connected with the terminals of a Grove's battery of five or six 




Fig. 168. 




Fig. 1 



152 



EXPLOSION OF CHLORINE AND HYDROGEN. 



cells. Chlorine is at once evolved at the positive pole (or that connected with the 
platinum in the battery), and hydrogen at the negative pole (attached to the zinc of 
the battery). It is ad visible to place the voltameter in a vessel of cold water, to 
prevent the hydrochloric acid from becoming too hot. The gas evolved during the 
first five minutes should be allowed to pass into a waste-jar, because, until the liquid 

becomes saturated with chlorine, 
the evolved gas does not contain 
exactly equal volumes of the 
constituent elements. A very 
thin glass bulb (C), about 2 
inches in diameter, blown upon 
a stout piece of tube, the ends of 
which have been drawn out to 
narrow open points (fig. 171), is 
then connected with the volta- 
meter by means of a caoutchouc 
tube. A similar caoutchouc tube 
is attached to the free end of the 
bulb. When the colour of the 
gas in the bulb (which should be 
shaded from sunlight) shows that it is completely filled, jthe caoutchouc tubes are 
well closed by nipper-taps (fig. 172), and the bulb detached from the voltameter. In 
this condition it may be kept in the dark for a long time without alteration or escape 
of gas. The mixture may be most effectively exploded by exposing it to the flash of 
light evolved by firing a mixture of nitric oxid.e gas with vapour of carbon disulphide.* 
For this purpose a cylinder may be filled with nitric oxide' (page 141) over water, 
closed with a glass plate, and placed mouth upwards upon the table : the glass plate 
being lifted for an instant, a few drops of bisulphide of carbon are poured into the 
cylinder, which is then shaken. The bulb containing the explosive mixture is 
suspended at some distance from the operator, and the gas cylinder is placed within 
a few inches of it (fig. 173). On applying a light to the cylinder, the flash Will cause 




Fig. 170. 




Fig. 172. Fig. 173. 

the immediate explosion of the mixture in the bulb, with production of strong fumes 
of hydrochloric acid. 

If the bulb be thin, no injury will be inflicted by the pieces of glass, or the 
operator may easily protect his face by a screen. 

The attraction of chlorine for hydrogen enables it to effect the decom- 
position of water. The solution of chlorine in water may be preserved 
in the dark without change ; but when exposed to light, it loses the 
smell of chlorine and becomes converted into weak hydrochloric acid, 
the oxygen being liberated; H 2 + C1 2 = 2 HCl + O.f The decomposi- 

* A mixture of equal volumes of chlorine and hydrogen may be exploded in a strong 
cylinder by the light of a piece of magnesium tape. The cylinder should be closed with a 
thin plate of mica, and placed on the table with its mouth upwards. 

f A portion of this oxygen combines with chlorine, producing hypochlorous acid and, 
as recently stated, perchloric acid. 



ACTION OF CHLORINE UPON HYDROGEN COMPOUNDS. 



153 



tion^ takes place much more quickly at a red heat, so that oxygen is 
obtained in abundance by passing a mixture of chlorine and steam 
through a red hot tube. 

For this experiment a porcelain tube is employed, which is loosely filled with 
fragments of broken porcelain, to expose a large heated surface. This tube is 
gradually heated to redness in a charcoal furnace (fig. 174). One end of it receives 
the mixture of chlorine with steam, obtained by passing the chlorine evolved from 
hydrochloric acid and manganese dioxide in A, through a flask (B) of boiling water. 
The other end of the tube is connected with a bottle (C) containing solution of 
potash, to absorb any excess of chlorine and the hydrochloric acid formed ; from this 
bottle the oxygen is collected over the pneumatic trough. 




Fig. 174. — Steam decomposed by chlorine. 

Since water is decomposed by chlorine, it is not surprising that most 
other hydrogen compounds are attacked by it. Ammonia (NH 3 ) is acted 
upon with great violence. If a stream of ammonia gas issuing from a tube 
connected with a flask in which solution of ammonia is heated (see fig. 146) 
be passed into a bottle of chlorine, it takes fire immediately, burning 
with a peculiar flame, and yielding thick white clouds of ammonium 



chloride; 4N"H 3 + CL 



3NH 4 C1 + K 



A piece of folded filter-paper 



dipped in strong ammonia, and immersed in a bottle of chlorine, will 
exhibit the same effect. When the chlorine is allowed to act upon 
ammonium chloride, its operation is less violent, and one of the most 
explosive substances is produced, which was formerly believed to be a 
chloride of nitrogen, but is probably a compound formed by the removal 
of a part of the hydrogen from ammonia, and the introduction of chlorine 
in its stead. 

Many of the compounds of hydrogen with carbon are also decomposed 
with violence by chlorine. When a piece of folded filter-paper is dipped 
into oil of turpentine (C 10 H 16 ), and afterwards into a bottle of chlorine, it 
bursts into a red flame, liberating voluminous clouds of carbon and 
hydrochloric acid. Acetylene (C 2 H 2 ) was found to explode spontaneously 
with chlorine when exposed to light (page 94). The striking decomposi- 
tion of olefiant gas (C 2 H 4 ) by chlorine on the approach of a flame has 
already been noticed (page 97). When a lighted taper is immersed in 
pure chlorine, it is extinguished; but if a little air be present, it continues to 



154 



BLEACHING BY CHLOBINE. 



"burn with a small red flame, the hydrogen only of the wax combining 
with the chlorine, whilst the carbon separates in black smoke, mixed 
with the hydrochloric fumes. When chlorine is brought in contact with 
the flame of a spirit-lamp, it renders the flame luminous by causing the 
separation of solid particles of carbon (page 105). It has been seen, in 
the case of defiant gas, that chlorine sometimes combines directly with 
the hydrocarbons. 

When marsh gas (CH 4 ) is diluted with an equal bulk of carbon dioxide 
to prevent violent action, and 4 volumes of chlorine are added for 
each volume of marsh gas, an oily liquid is gradually formed under the 
influence of daylight. This oily liquid is a mixture of chloroform and 
carbon tetrachloride, the production of which is explained by the follow- 
ing equations : — 

CH 4 + Cl 6 = 3HC1 + CHC1 3 {Chloroform). 

OH 4 + Cl 8 = 4HC1 + CC1 4 {Carbon tetrachloride). 

It is evident from these equations that chlorine is capable, not only of 
removing hydrogen from a compound, but also of taking its place, atom 
for atom — a mode of action which gives rise to a very large number of 
chlorinated products from organic substances. 

The attraction of chlorine for hydrogen enables the moist gas to act as 
an oxidising agent. Thus, if marsh gas and chlorine be mixed in the 
presence of water, and exposed to daylight, the water is decomposed, its 
hydrogen combining with the chlorine, and its oxygen with the carbon 
of the marsh gas ; CH 4 + 2H 2 + Cl 8 = C0 2 + 8HC1 . 

103. The powerful bleaching effect of chlorine upon organic colouring 
matters is now easily understood. If a solution of chlorine in water be 
poured into solution of indigo (sulphindigotic acid), the blue colour of the 
indigo is discharged, and gives place to a comparatively light yellow 
colour. The presence of water is essential to the bleaching of indigo by 
chlorine, the dry gas not affecting the colour of dry indigo. The indigo 
is first oxidised at the expense of the water and converted into iscdine, 
which is then acted upon by the chlorine and converted into chlorisatine, 
having a brownish-yellow colour — 



{Indigo) +H 9 + CL 



C s H 5 NO 

CoH=NO„(/*a«»e) + CL 



C 8 H 6 N"0 2 Ratine) + 2HC1] 

C 8 H 4 C1N0 2 (Chlorisatine) + HC1 . 




Fig. 175. 



Nearly all vegetable and animal colouring matters 
contain carbon, hydrogen, nitrogen, and oxygen, 
and are converted by moist chlorine into products 
of oxidation or chlorination which happen to be 
colourless, or nearly so. 

That dry chlorine will not bleach may be shown by 
shaking some oil of vitriol in a bottle of the gas and 
allowing it to stand for an hour or two, so that the acid 
may remove the whole of the moisture. If a piece of 
crimson paper be dried at a moderate heat and suspended 
in the bottle while warm, it will remain unbleached for 
hours ;• but a similar piece of paper suspended in a bottle 
of moist chlorine will be bleached almost immediately. 
If characters be written on crimson paper with a wet 
brush, and the paper placed in a jar beside a bottle of 
chlorine (fig. 175), it will be found on removing the 



stopper that white characters soon make their appearance on the red ground. 



CHLORIDE OF LIME. 155 

If a collection of coloured linen or cotton fabrics, or of artificial flowers, be exposed 
to the action of moist chlorine gas or of chlorine water, those which are dyed with 
organic colouring matters will be bleached at once, whilst the mineral colours will for 
the most part remain unaltered. Green leaves immersed in chlorine acquire a rich 
autumnal brown tint, and are eventually bleached. All flowers are very readily 
bleached by this gas. 

Chlorine is very extensively employed for bleaching linen and cotton, 
the gas acting upon the colouring matter without affecting the fibre ; but 
silk and wool present much less resistance to chemical action, and would 
be much injured by chlorine, so that they are always bleached by 
sulphurous acid gas. 

Neither chlorine itself nor its solution in water can be very conveniently 
employed for bleaching on the large scale, on account of the irritating 
effect of the gas, so that it is usual to employ it in the form of chloride 0/ 
lime, from which it can be easily liberated as it is wanted. 

104. Chloride of lime or bleaching powder is prepared by passing 
chlorine gas into boxes of lead or stone in which a quantity of slaked 
lime is spread out upon shelves. The lime absorbs nearly half its weight 
of chlorine, and forms a white powder, which has a very peculiar smell, 
somewhat different from that of chlorine. 

The formula of chloride of lime is generally written CaOCl 2 . 

The constitution of chloride of lime appears doubtful. When the calcium hydrate 
Ca(HO) 2 , is acted on by chlorine, the simplest reaction would be Ca(HO). 2 + Cl 2 
= CaCl(ClO) + H 9 0, according to which the chloride of lime would result from the 
replacement of one of the HO groups by CI, and of the other by CIO ; but this would 
require the calcium hydrate to absorb nearly an equal weight of chlorine, whereas the 
amount never exceeds half this quantity. 

According to another view, the chloride of lime is a mixture of calcium hypo- 
chlorite Ca(C10) 2 with calcium oxychloride Ca 3 0oCl 2 , produced by the reaction 
4Ca(HO) 2 + Cl 4 = Ca(C10) 2 + Ca 3 2 Cl 2 + 4H 2 0, which would require the absorption of 
nearly half its weight of chlorine by the calcium hydrate. A more recent theory 
regards the chloride of lime as containing calcium chloride, together with the 
compound CaHC10 2 , resulting from the substitution of CI for H in CaH 2 2 ; but since 
calcium chloride absorbs water and becomes wet on exposure to air, whilst good 
chloride of lime remains dry, it is difficult to admit the correctness of this view. The 
analyses which support this theory would also agree equally well with the formula 
Ca 3 (OH) 2 (OCl) 2 Cl 2 , which would explain the tendency of chloride of lime to yield, 
among the products of its decomposition, calcium chloride CaCl 2 , calcium hypo- 
chlorite Ca(OCl) 2 and calcium hydrate Ca(OH) 2 . 

Practically, the constitution of chloride of lime itself is of less importance than 
that of the solution obtained by treating it with water, which is generally admitted 
to contain calcium hypochlorite Ca(C10) 2 and calcium chloride CaCl 2 ,* with some 
calcium hydrate Ca(HO) 2 , of which a large quantity is left in the undissolved 
residue. 

Taking each of the three views above mentioned, the action of water upon chloride 
of lime would be represented by one of the following equations : (1) 2CaCl(C10) 
= CaCl 2 + Ca(C10) 2 ; (2) Ca(C10) 2 + Ca 3 2 Cl 2 + 2H 2 = Ca(ClO), + CaCl 2 + 2Ca(H0) 2 ; 
(3) 2CaHC10 2 + CaC.l 3 = Ca(C10) 2 + CaCl 2 + Ca(HO) £ . 

If the solution of chloride of lime be added to blue litmus, it will be 
found to exert little bleaching action ; but on adding a little acid (sul- 
phuric, for example), the blue colour will be discharged, the acid setting 
free the chlorine, which acts upon the colouring matter. 

Ca(C10) 2 + Cad 2 + 2H 2 S0 4 = 2CaS0 4 + 2H 2 + Cl 4 . 

Solution of chloride of lime. 

Even carbonic acid will develop the bleaching property of chloride of 
lime, so that the above mixture may be decolorised by breathing into it 
through a glass tube. 



156 DISINFECTION BY CHLORINE. 

When chloride of lime is used for bleaching on the large scale, the stuff 
to be bleached is first thoroughly cleansed from any grease or weaver's dress- 
ing, by boiling it in lime-water and in a weak solution of soda, and is then 
immersed in a weak solution of the chloride of lime. This, by itself, how- 
ever, exerts very little action upon the natural colouring matter of the 
fibre, and the stuff is therefore next immersed in very dilute sulphuric 
acid, when the colouring matter is so far altered as to become soluble in 
the alkaline solution in which it is next immersed, and a repetition of 
these processes, followed up by a thorough rinsing, generally perfects the 
bleaching. 

The property possessed by acids of liberating chlorine from the chloride 
of lime is applied, in calico-printing, to the production of white patterns 
upon a red ground. The stuff having been dyed with Turkey red, the 
pattern is imprinted upon it with a discharge consisting of an acid (tar- 
taric, phosphoric, or arsenic) thickened with gum. On passing the fabric 
through a bath of weak chloride of lime, the colour is discharged only at 
those parts to which the acid has been applied, and where, consequently, 
chlorine is liberated. 

The explanation above given of the bleaching effect of chlorine may 
probably be applied also to its so-called disinfecting properties. The 
atmosphere, in particular localities, is occasionally contaminated with 
poisonous substances, some of which are known only by their injurious 
effects upon the health, their quantity being so small that they do not 
appear in the results of the analysis of such air. Since, however, these 
substances appear to be acted upon by the same agents which are usually 
found to decompose organic compounds, they are commonly believed to 
be bodies of this class, and chlorine has been very commonly employed to 
combat these insidious enemies to health, since Guy ton de Morveau, in 
the latter part of the last century, made use of it to destroy the odour 
arising from the bodies interred in the vaults beneath the cathedral of Dijon. 

Among the offensive and unhealthy products of putrefaction of animal 
and vegetable matter, sulphuretted hydrogen, ammonia, and bodies simi- 
larly constituted, are found. That chlorine breaks up these hydrogen 
compounds is well known, and hence its great value for removing the 
unwholesome properties of the air in badly-drained houses, &c. 

Chloride of lime is one of the most convenient forms in which to apply 
chlorine for the purposes of fumigating and disinfecting. If a cloth 
saturated with the solution be suspended in the air, the carbonic acid gas 
in the latter causes a slow evolution of hypochlorous acid, which is even a 
more powerful disinfectant than chlorine itself. In extreme cases, where 
a rapid evolution of chlorine is required, the bleaching" powder is placed 
in a plate, and diluted sulphuric acid is poured over it, or the powder may 
be mixed with half its weight of powdered alum in a plate, when a pretty 
rapid and regular escape of chlorine will ensue. 

105. The discovery of chlorine, and the discussions which ensued with 
respect to its real nature, contributed very largely to the advancement of 
chemical science. About the year 1770, the Swedish chemist Scheele 
(who afterwards discovered oxygen) first obtained chlorine by heating 
manganese ore with muriatic acid. 

The construction which Scheele put upon the result of this experiment 
was one which was consistent with the chemistry of that date. He sup- 



PREPARATION OF HYDROCHLORIC ACID. 



157 



posed the muriatic acid to have been deprived of phlogiston, and hence 
chlorine was termed by him dephlogisticated muriatic acid. This phlo- 
giston had long been a subject of contention among philosophers, having 
been originally assumed to exist in combination with all combustible 
bodies, and to be separated from them during their combustion. To- 
wards the decline of the phlogistic theory, attempts were made to prove 
the identity of this imaginary substance with hydrogen, which shows 
how very nearly Scheele's reasoning approached to the truth, even with 
the very imperfect light which he then possessed. Berthollet's move- 
ment was retrograde when, ten years afterwards, he styled chlorine oxy- 
genised muriatic or oxy muriatic acid; but the experiments of Gay-Lussac 
and Thenard, and more particularly those of Davy in 1811, proved de- 
cisively that hydrochloric acid was composed of chlorine and hydrogen, 
and that the effect of the black oxide of manganese in Scheele's experi- 
ment was to remove the hydrogen in the form of water, thus setting the 
chlorine at liberty. 

Hydrochloric Acid. 

HC1 = 36*5 parts by weight = 2 volumes. 

106. This acid is found in nature among the gases emanating from 
active volcanoes, and occasionally in the spring and river waters of vol- 
canic districts. For use it is always prepared artificially by the action of 
sulphuric acid upon common salt — 

NaCl + H 2 S0 4 = HC1 + NaHS0 4 

Common salt. Hydrosodic sulphate. 

the sodium of the common salt changing places with the hydrogen of the 
sulphuric acid. 

300 grains of common salt (pre- 
viously dried in an oven) are intro- 
duced into a dry Florence flask (fig. 
176), to which has been fitted, by 
means of a perforated cork, a tube 
bent twice at right angles, to allow 
the gas to be collected by downward 
displacement. Six fluid drachms of 
strong sulphuric acid are poured 
upon the salt, and the cork having 
been inserted, the flask is very 
gently heated, in order to promote 
the disengagement of the hydro- 
chloric acid gas, which is collected 
in a perfectly dry bottle, the mouth . 
of which, when full, may be covered 
with a glass plate smeared with a 
little grease. While being filled, the 
bottle may be closed with a per- 
forated card. 

Common salt in powder sometimes froths to a very inconvenient extent with sul- 
phuric acid ; it is therefore often preferable to employ fragments of rock salt or of 
fused salt, prepared by fusing the common salt in a clay crucible, and pouring on to 
a clean dry stone. 

A very regular supply of hydrochloric acid gas is obtained from \\ oz. of sal 
ammoniac in lumps, and \\ oz. (measured) of sulphuric acid. 

The bottle will be known to be filled with gas by the abundant escape 
of the dense fumes which hydrochloric acid gas, itself transparent, pro- 
duces by condensing the moisture of the air ; for since the gas is much 




Fig 



Preparation of hydrochloric acid gas. 



158 



HYDROCHLORIC OR MURIATIC ACID. 



heavier than air (sp. gr. 1*247), it will not escape in any quantity from 
the bottle until the latter is full. The odour of the gas is very suffocat- 
ing, but not nearly so irritating as that of chlorine. The powerful 
attraction for water is one of the most important properties of hydrochloric 
acid gas. 

If a jar of hydrochloric acid gas be closed with a glass plate and inverted under 
water, it will be found on removing the plate that the gas is absorbed with great 
rapidity, the water being forced up into the bottle by the pressure of the external air 
in proportion as the gas is absorbed. 

A Florence flask is more convenient than a gas-bottle for this experiment. It must 
be perfectly dry, and thoroughly well filled with the gas, which may be allowed to 
escape abundantly from the mouth. The tube delivering the hydrochloric acid gas 
must be slowly withdrawn, so that the vacancy may be filled by gas, and not by air. 
The flask is then closed with the thumb, and opened under water, which will enter it 
with great violence. The experiment may also be made as in the case of ammonia 
(fig. 177, see page 125). 





Fig. 177. 



Fig. 178. — Preparation of solution of 
hydrochloric acid. 



The liquid hydrochloric, or muriatic acid of commerce, is a solution of 
the gas in water, and may be recognised by the grey fumes, with the 
peculiar odour of the acid, which it evolves when exposed to the air. 
One pint of water at a temperature of 40° F., is capable of absorbing 480 
pints of hydrochloric acid gas, forming 1J pint of the solution, having the 
specific gravity 1*21. The strength of the acid purchased in commerce is 
usually inferred from the specific gravity, by reference to tables indicat- 
ing the weight of hydrochloric acid contained in solutions of different 
specific gravities. The strongest hydrochloric acid (sp. gr. 1*21) contains 
43 per cent, by weight of the gas. At - 18° C. it deposits crystals of 
HC1.4Aq. The common acid has usually a bright yellow colour, due 
to the accidental presence of a little ferric chloride (Fe 2 Cl 6 ). 

This acid is produced in enormous quantities in the alkali works, where 
common salt is decomposed by sulphuric acid in order to convert it into 
sodium sulphate, as a preliminary step to the production of sodium 
carbonate. The alkali manufacturer is compelled to condense the gas, for 
it is found to wither up the vegetation in the neighbourhood. For this 
purpose the hydrochloric acid gas is drawn up from the furnace through 
vertical cylinders filled with coke, over which streams of water are made 
to trickle. The water absorbs the acid, and is drawn off from below. 

In preparing a pure solution of the acid for chemical use on a small scale, the 
gas prepared as above may be passed into a small bottlecontaining a very little water, 



HYDEOCHLOEIC ACID. 



159 



to wash the gas, "or remove any sodium sulphate which may splash over, and then into 
a bottle about two-thirds filled with distilled water, the tube delivering the gas pass- 
ing only about -^ inch below the surface, so that the heavy solution of hydrochloric 
acfd may fall to the bottom, and fresh water may be presented to the gas (fig. 178). 
For ordinary use, an acid of suitable strength is obtained by passing the gas from 6 
ounces of common salt and 10 ounces of sulphuric acid into 7 (measured) ounces of 
water until its bulk has increased to 8 ounces. The bottle containing the water 
should be surrounded with cold water, since the absorption of hydrochloric acid by 
water is attended with evolution of heat. 

Pure solution of hydrochloric acid is sometimes prepared on the large scale by 
allowing concentrated sulphuric acid to run into the common hydrochloric acid, when 
the gas is evolved, which is washed and passed into water. 

When the concentrated solution of hydrochloric acid is heated in a re- 
tort it evolves abundance of hydrochloric acid gas, rendering it probable that 
it is not a true chemical compound of water with the acid. The evolution 
of gas ceases- when the remaining liquid contains 20 per cent, of acid (and 
has a sp. gr. of 1-10). If a weaker acid than this be heated, it loses 
water until it has attained this strength, when it distils unchanged* 

The concentrated solution forms a very convenient source from which to procure 
the gas. It may be heated in a flask, and the gas dried by passing through a bottle 
filled with fragments of pumice-stone wetted with concentrated sulphuric acid, being 
collected over the mercurial trough (fig. 17y). 




Fig. 179. 

The avidity with which water absorbs hydrochloric acid is the more 
remarkable, because this gas can be liquefied only under a very high 
pressure, amounting at the ordinary temperature to about 40 atmospheres. 

The liquefied hydrochloric acid has comparatively little action even 
upon those metals which decompose its aqueous solution with great 
violence ; quicklime is unaffected by it, and solid litmus dissolves in it 
with a faint purple colour, instead of the bright red imparted by the 
aqueous hydrochloric acid. Dry hydrochloric acid gas is not absorbed by 
calcium carbonate. 

The injurious action of hydrochloric acid gas upon growing plants is 
probably connected with its attraction for water. If a spray of fresh 
leaves is placed in a bottle of hydrochloric acid, it becomes at once brown 
and shrivelled. 

107. Action of hydrochloric acid upon metals. — Those metals which 
have the strongest attraction for oxygen will also generally have the 

* The proportion of acid thus retained by the water varies directly with the atmospheric 
pressure to which it is exposed during the distillation. 



160 ACTION OF HYDROCHLORIC ACID ON METALLIC OXIDES. 

strongest attraction for chlorine, so that in respect to their capability of 
decomposing hydrochloric acid, they may be ranked in pretty nearly the 
same order as in their action upon water (p. 11). Since, however, the 
attraction of chlorine for the metals is generally superior to that of oxygen, 
the metals are more easily acted upon by hydrochloric acid than by water, 
the metal taking the place of the hydrogen, and a chloride of the metal 
being formed. 

Even silver, which does not decompose water at any temperature, is 
dissolved, though very slowly, by boiling concentrated hydrochloric acid, 
the chloride of silver formed being soluble in the strong acid, though it 
may be precipitated by adding water. 

Gold and platinum, however, are not attacked by hydrochloric acid; but 
if a little free chlorine be present, it converts them into chlorides. 

Iron and zinc decompose the acid very rapidily in the cold, forming 
ferrous chloride and zinc chloride, and liberating hydrogen; Fe + 2HC1 
= FeCl 2 +H 2 . 

When potassium or sodium is exposed to hydrochloric acid gas, it im- 
mediately becomes coated with a white crust of chloride, which partly 
protects the metal from the action of the gas; but when these metals are 
heated to fusion in hydrochloric acid gas, they burn vividlv; Na + HCl 
= KaCl + H. 

The composition of hydrochloric acid may be exhibited by confining a 
measured volume of the gas over mercury (see fig. 82, page 84), and passing 
up a freshly-cut pellet of sodium. On gently agitating 
the tube, the gas diminishes in volume, and after 
a time will have contracted to one-half, and will be 
found to have all the properties of hydrogen. This 
result confirms that obtained by synthesis, as de- 
scribed above, that 2 volumes of hydrochloric acid 
contain 1 volume of hydrogen and 1 volume of 
chlorine. 

The electrolysis of hydrochloric acid is exhibited in the 

V-tube represented in fig. 180, where the platinum plate p in 

the closed limb o is connected with a platinum wire sealed 

into the glass ; the other limb h is open. If the closed limb 

he entirely filled with strong hydrochloric acid, and connected 

with the negative pole of a battery composed of five or six 

Grove's or Bunsen's cells, the positive pole being connected 

with h, hydrogen will rapidly collect in the closed limb, 

whilst the odour of chlorine will be perceived in the open 

limb. As soon as the liquid fills the open limb, the wire h is 

Fig. 180. withdrawn, this limb closed with the thumb, and the hydrogen 

transferred to it by inclining the tube! After testing the 

hydrogen with a match, the poles of the battery may be reversed, when the chlorine 

will collect as gas in the closed limb, as soon as the hydrochloric acid has become 

saturated with it. 

108. Action of hijdrocliloric acid upon metallic oxides. — Asa general 
rule, it may be stated that, when hydrochloric acid acts upon the oxide of 
a metal, the results are water and a chloride of the metal, in which each 
atom of oxygen in the oxide has been displaced by 2 atoms of chlorine. 

Thus, silver oxide acted on by hydrochloric acid gas gives water and 
silver chloride ; Ag 2 + 2HC1 = H 2 + 2AgCl . 

Suboxide of copper (cuprous oxide) yields water and subchloride of 
copper (cuprous chloride) ; Cu 2 + 2HC1 = H 2 + Cu 2 Cl 2 . 




OXIDES OF CHLORINE. 161 

Ferric oxide gives water and ferric chloride ; Fe 2 3 + 6HC1 = 3H 2 
+ Fe 2 CL. 

With stannic oxide, water and stannic chloride are obtained ; SnO., 
+ 4HCl = 2H 2 + SnCl 4 . 

Antimonious oxide is converted into water and antimonious chloride; 

Sb 2 3 + 6HC1 = 3H 2 + 2SbCl 3 . 

109. In cases where the corresponding chloride does not exist, or is not 
stable under the conditions of the experiment, a chloride is formed con- 
taining less chlorine than is equivalent to the oxygen in the oxide, and 
the balance is evolved in the free state. Thus, when manganese sesqui- 
oxide and dioxide are heated with hydrochloric acid — 

Mn 9 3 + 6HC1 = 3H 2 + 2MnCl 2 + CI 2 ; 
Mn0 2 + 4HC1 = 2H 2 + MnCl 2 + Cl 2 . 

Chromic anhydride, a chloride corresponding to which is not known to 
exist, when heated with hydrochloric acid, yields chromic chloride and 
chlorine ; 2Cr0 3 + 12HC1 = 6H 2 + Cr,Cl 6 + Cl 6 . 

Every metallic oxide containing 1 atom of oxygen has a corresponding 
chloride of a stable character, but ihe higher oxides less frequently form 
corresponding chlorides endowed with any stability. 

Compounds of Chlorine with Oxtgex. 

110. It is worthy of notice, that whilst chlorine and hydrogen so readily 
unite, there is no method by which chlorine can be made to combine in a 
direct manner with oxygen, all the compounds of these elements having 
been hitherto obtained only by indirect processes. An excellent illustra- 
tion is thus afforded of the fact, that the more .closely substances resemble 
each other in their chemical relations, the less will be their tendency to 
combine; for chlorine and oxygen are both highly electro-negative bodies, 
and therefore, having both a powerful attraction for the electro-positive 
hydrogen, their attraction for each other is of a very low order. 

111. Hypoehlorous anhydride (C1 2 0) is of some practical interest in 
connexion with chloride of lime, chloride of soda, and other bleaching 
compounds. It is prepared by passing dry chlorine gas over dry preci- 
pitated mercuric oxide, and condensing the product in a tube surrounded 
with a mixture of ice and salt; HgO + Cl 4 = HgCl 2 + C1 2 . 

The hypoehlorous anhydride is thus obtained as a deep red liquid, which 
boils at 19° F., evolving a yellow vapour twice as heavy as air, and having 
a very powerful and peculiar odour. This vapour is remarkably explosive, 
the heat of the hand having been known to cause its separation into 
its constituents, when 2 volumes of the vapour yield 2 volumes of 
chlorine and 1 volume of oxygen. As might be expected, most substances 
which have any attraction for oxygen or chlorine will decompose the gas, 
sometimes with explosive violence. Even hydrochloric acid decomposes 
it : 1 volume of hypoehlorous acid gas is entirely decomposed by 2 
volumes of hydrochloric acid, yielding water and chlorine ; C1 + 2HC1 
= H 2 + C1 4 . Hypoehlorous anhydride is a powerful bleaching agent, 
both its chlorine and oxygen acting upon the colouring matter in the 
manner explained at page 154. 

Hypoehlorous anhydride is absorbed in large quantity by water ; the 
solution is supposed to contain hypoehlorous acid, HCIO, for H 2 + 

L 



162 HYPOCHLOROUS ACID. 

C1 2 = 2HC10 : but HC10 lias not been obtained in the separate state. 
The solution may be very readily prepared by shaking the red oxide of 
mercury with water in a bottle of chlorine as long as the gas is absorbed. 
The greater part of the mercuric chloride which is produced combines 
with the excess of oxide to form a brown insoluble oxychloride, whilst 
the hypochlorous acid and a little mercuric chloride remain in solution. 
This solution is a most powerful oxidising and bleaching agent ; it erases 
writing ink immediately, and does not corrode the paper if it be carefully 
washed. Printing ink, which contains lamp black and grease, is not 
bleached by hypochlorous acid, so that this solution is very useful for 
removing ink stains from books, engravings, &c. 

The action of some metals and their oxides upon solution of hypo- 
chlorous acid is instructive. Iron seizes upon the oxygen, whilst the 
chlorine is liberated ; copper takes both the oxygen and chlorine ; whilst 
silver combines with the chlorine, and liberates oxygen. Oxide of lead 
(PbO) removes the oxygen, becoming peroxide of lead (Pb0 2 ), and liber- 
ating chlorine, but oxide of silver converts the chlorine into chloride of 
silver, and liberates the oxygen ; Ag 2 + Cl 2 = 2AgCl + 2 . 

The salts of hypochlorous acid, or hypochlorites, are not known in a 
pure state, but are obtained in solution by neutralising the solution of 
hypochlorous acid with bases.* They are decomposed even by carbonic 
acid, with liberation of hypochlorous acid. 

When the solution of a hypochlorite is boiled, it becomes converted 
into a mixture of chloride and chlorate ; thus — 



3KC10 = 


= KCIO3 


+ 


2KC1 


Potassium 


Potassium 




Potassium 


ypochlorite. 


chlorate. 




chloride. 



This change is turned to practical account in the manufacture of chlorate 
of potash. It is much hindered by the presence of an excess of alkali. 
The solution of hypochlorous acid itself, when exposed to light, is 
decomposed into chloric acid and free chlorine ; 5HC10 = HC10 3 -r-2H 2 
+ C1 4 . 

112. Chloride of lime (calx chlorata, see p. 155) is the most important 
compound formed by hypochlorous acid. Its formula has already been 
discussed at p. 155. When this compound is distilled with a small 
quantity of diluted sulphuric acid, a solution of hypochlorous acid is 
obtained ; but if an excess of acid be used, free chlorine is the result. 

Bleaching powder is liable to decomposition when kept, evolving 
oxygen, and becoming converted into calcium chloride, which attracts 
moisture greedily, and renders the bleaching powder deliquescent It has 
been known to shatter the glass bottle in which it was preserved, in con- 
sequence of the accumulation of oxygen ;f CaOCl 2 = CaCl 2 + . 

When a solution of a salt of manganese or cobalt is added to solution 
of chloride of lime, a black precipitate of Mn0 2 or Co 2 3 is obtained. If 
this precipitate be boiled with an excess of solution of chloride of lime, it 
causes a rapid disengagement of oxygen, in some manner that has not yet 
been clearly explained. Large quantities of oxygen are easily obtained 

* Calcium hypochlorite has been obtained, in crystals of the formula Ca(C10) 2 .4H. 2 
by evaporating solution of chloride of lime in vacuo over sulphuric acid and potash 
( Kingzett). 

f When rapidly made and hastily packed, it has been known to become so hot as to set 
lire to the casks. 



CHLORATE OF POTASH. 



163 



by adding a few drops of solution of cobalt nitrate to solution of chloride 
of lime, and applying a gentle heat. 

Old chloride of lime always contains calcium chlorate j 6CaOCi 9 
= 5CaCl 2 + Ca(Cl0 3 ) 2 . 

Sodium hypochlorite, which is very useful for removing ink, is prepared 
in solution by decomposing solution of chloride of lime with solution of 
sodium carbonate, and separating the calcium carbonate by filtration. 
The solution is generally called " chloride of soda " (liquor sodcechloratce). 

113. Chloric acid (HC10 3 ). — This acid is appropriately studied here, 
since its salts are usually obtained by the decomposition of the hypo- 
chlorites. The only chlorate which possesses any great practical importance 
is potassium chlorate (KC10 3 ), which is largely employed as a source of 
oxygen, as an ingredient of several explosive compositions, and in the 
manufacture of lucifer matches. 

Potassium chlorate or chlorate of potash. — 
The simplest method of obtaining this salt 
consists in passing an excess of chlorine rapidly 
into a strong solution of potash (fig. 181), 
when the liquid becomes hot enough to 
decompose the hypochlorite first formed into 
potassium chloride, which remains in solution, 
and potassium chlorate, which is deposited in 
tabular crystals, the ultimate result being 
expressed by the equation — 

6KHO + Cl 6 = KC10 3 + 5KC1 + 3H 2 0. 

If potassium carbonate or a weak solution of 
potash be employed, the liquid will require Fig. 181. 

boiling after saturation with chlorine, in order to convert the hypochlorite 
into chlorate. 

The following proportions will be found convenient for the preparation of potassium 
chlorate on the small scale as a laboratory experiment. 300 grains of potassium 
carbonate are dissolved, in a beaker, with 2 measured ounces of water. 600 grains of 
common salt are mixed with 450 grains of binoxide of manganese, and very gently 
heated in a flask (fig. 181) with a mixture of 1 \ ounce (measured) of strong sulphuric 
acid and 4 ounces (measured) of water, the evolved chlorine being passed through a 
rather Avide bent tube into the solution of potassium carbonate. 

At first no action will appear to take place, although the solution absorbs the 
chlorine ; because the first portion of that gas converts the potassium carbonate into 
a mixture of potassium hypochlorite, potassium chloride, and hydropotassic carbonate, 
some crystals of which will probably be deposited — 

2K 2 C0 3 + Clo + H 2 = KC1 + KCIO + 2KHC0 3 . 

On continuing to pass chlorine, these crystals will redissolve, and brisk efferves- 
cence will be caused by the expulsion of the carbonic acid gas; 2KHC0 3 + 01 2 = KC1 
+ KC10 + H 2 + 2C0 2 . 

When this effervescence has ceased, and the chlorine is no longer absorbed by the 
liquid, the change is complete, the ultimate result being represented by the equa- 
tion K 2 C0 3 + C1 2 = KC1+KC10 + C0 2 . The solution (which often has a pink 
colour, due to a little potassium ferrate) is now poured into a dish, boiled for two 
or three minutes, filtered, if necessary, from any impurities (silica, &c. ), derived from 
the potassium carbonate, and set aside to crystallise. The ebullition has converted 
the potassium hypochlorite into chlorate and chloride of potassium ; 3KC10 = KC10 3 
+ 2KC1. The latter, being soluble in about three times its weight of cold water, is 
retained in the solution, whilst the chlorate, which would require about sixteen times 
its weight of cold water to hold it dissolved, is deposited in brilliant rhomboidal 




164 PREPARATION OF CHLORATE OF POTASH. 

tables. These crystals may be collected on a filter, and purified from the adhering 
solution of potassium chloride by pressure between successive portions of filter-paper. 
If they be free from chloride, their solution in water will not be changed by silver 
nitrate, which would yield a milky precipitate of silver chloride if that impurity were 
present. Should this be the case, the crystals must be redissolved in a small quantity 
of boiling water, and recrystallised. 

The above processes for preparing potassium chlorate are far from 
economical, since five-sixths of the potash are converted into chloride, 
being employed merely to furnish oxygen to convert the chlorine into 
chloric acid. In manufacturing the chlorate upon the large scale, a much 
cheaper material, lime, is used to furnish the oxygen, one molecule of 
potassium carbonate being mixed with six molecules of slaked lime and 
the damp mixture saturated with chlorine. On treating the mass with 
boiling water, a solution is obtained which contains potassium chlorate 
and calcium chloride : the latter, being very soluble, remains in the liquor, 
from which the chlorate crystallises on cooling. The ultimate result of 
the action of chlorine upon the mixture of potassium carbonate and lime 
is thus expressed ; K 2 C0 3 + 6Ca(HO) 2 + Cl 12 = 2KC10 3 + 5CaCl 2 + CaC0 3 
+ 6H 2 . 

A still cheaper salt of potassium, the chloride, has recently been em- 
ployed with great economy as a substitute for the carbonate. Lime is 
mixed with water, and saturated with chlorine gas in close leaden tanks ; 
2Ca(OH) 2 (calcium hydrate) + Cl 4 = Ca(0Cl) 9 (calcium hypochlorite) 
+ CaCl 2 (calcium chloride) + 2H 2 0. The liquid is boiled down, when 
the calcium hypochlorite is decomposed into calcium chlorate and chloride \ 
3Ca(OCl) 2 = 2Ca(C10 3 ) 2 + CaCl 2 . The calcium chlorate is now decom- 
posed by boiling with potassium chloride, when it yields calcium chloride 
which remains in solution, and potassium chlorate which separates in 
crystals as the solution cools ; Ca(C10 3 ) 2 + 2KC1 = CaCl 2 + 2KC10 3 . 

Chloric acid (HCI0 3 ) may be procured by decomposing a solution of 
potassium chlorate with hydrofluosilicic acid, when the potassium is 
deposited as an insoluble silico-nuoride, and chloric acid is found in the 
solution * — 

2KC10 3 + H 2 SiF 6 = 2HC10 3 + K 2 SiF 6 

Hydrofluosilicic acid. 

On evaporating the solution at a temperature not exceeding 100° F., 
the chloric acid is obtained as a yellow liquid, with a peculiar pungent 
smell. 

In its chemical characters, chloric acid bears a very strong resemblance 
to nitric acid, but is far more easily decomposed. It cannot even be kept 
unchanged for any length of time, and at temperatures above 104° F. it is 
decomposed into perchloric acid, chlorine, and oxygen; 4HC10 3 = 2HC10 4 
+ H 2 + C1 2 + S . 

Chloric acid is one of the most powerful oxidising agents : a drop of it 
will set fire to paper, and it oxidises phosphorus (even the amorphous 
variety) with explosive violence. 

Chlorates. — Chloric acid, like nitric, is monobasic, containing only 
one atom of hydrogen replaceable by a metal. The chlorates resemble the 
nitrates in their oxidising power, but generally act at lower temperatures, 
in consequence of the greater facility with which the chlorates part with 
their oxygen. 

* 440 grain measures of hydrofluosilicic acid of sp. gr. 1078 will decompose 100 grains 
of the chlorate. 



DETONATING COMPOSITIONS. 



165 




A grain or two of potassium chlorate, rubbed in a mortar with a little sulphur, for 
example, detonates violently, evolving a powerful odour of chloride of sulphur. Potas- 
sium chlorate and sulphur were used in some of the first per- 
cussion caps, but being found to corrode the nipple of the gun, 
they gave place to the anticorrosive caps containing mercuric 
fulminate. 

If a little powdered chlorate be mixed on a card with some 
black antimony sulphide, and wrapped up in paper, the mixture 
will detonate when struck with a hammer. 

A mixture of this description is employed in the friction tubes 
used for firing cannon. These are small tubes (A, fig. 182) of 
sheet copper (for military) or of quill (for naval use), filled with 
gunpowder : in the upper part of the tube a small copper rasp 
(B) is tightly fixed across it, and on each side of the rasp a pellet 
is placed containing 12 parts of potassium chlorate, 12 of antimony 
sulphide, and 1 of sulphur, these ingredients being worked up 
into a paste with a solution of an ounce of shellac in a pint of 
spirit of wine. The friction tube is fixed in the vent of the gun, 
aud the copper rasp quickly withdrawn by a cord in the hands 
of the gunner, when the detonating pellets explode and fire the 
powder. 

The earliest lucifer matches were tipped with a mixture of 
potassium chlorate, antimony sulphide, and starch, and were 
kindled by drawing them briskly through a doubled piece of sand- 
paper. 

At high temperatures the chlorates act violently upon combustible 
bodies. A little potassium chlorate sprinkled upon red hot coals causes a 
very violent deflagration. If a little of the chlorate 
be melted in a deflagrating spoon, and plunged into 
a bottle or flask containing coal gas (fig. 183), the salt 
burns with great brilliancy, its oxygen combining 
with the carbon and hydrogen in the gas; which 
becomes in this case the supporter of combustion. 
The flask may be conveniently filled with coal gas 
by inverting it, and passing a flexible tube from the 
gas pipe up into it. 

Potassium chlorate is much used in the manu- 
facture of fireworks, especially as an ingredient of 
coloured fire compositions, which generally consist of 
potassium chlorate mixed with sulphur, and with 
some metallic compound, to produce the desired 
colour in the flame. They are not generally made of 
the best quality on the small scale, from want of attention to the very 
finely-powdered state of the ingredients, the absence of all moisture, and 
the most intimate mixture. 

If these precautions be attended to, the following prescription will give very good 
coloured fires : — 

Pxd fire,. — 40 grains of nitrate of strontia. thoroughly dried over a lamp, are mixed 
with 10 grains of chlorate of potash, and reduced to the finest possible powder. In 
another mortar 13 grains of sulphur are mixed with 4 grains of black sulphide of 
antimony (crude antimony). The two powders are then placed upon a sheet of 
paper, and very intimately mixed with a bone knife, avoiding any great pressure. 
A little heap of the mixture touched with a red hot iron ought to burn with a uniform 
red flame, the colour being due to the strontium. 

Blue fire. — 15 grains of chlorate of potash are mixed with 10 grains of nitrate of 
potash and 30 grains of oxide of copper, in a mortar. The finely-powdered mixture 
is transferred to a sheet of paper, and mixed, by a bone knife, with 15 grains of 
sulphur. The colour of the fire is given chiefly by the copper. 




166 COLOURED FIRES. 

Green fire. — 10 grains of chlorate of baryta are mixed with 10 grains of nitrate of 
bartyta in a mortar, and afterwards on paper with 12 grains of sulphur. The barium 
is the cause of the bright green colour of the flame. 

These compositions are rather dangerous to keep, since they are liable to spon- 
taneous combustion. 

White gunpowder is a mixture of two parts of chlorate of potash with one part of 
dried yellow prussiate of potash, and one part of sugar, which explodes very easily 
under friction or percussion. 

The decomposition of potassium chlorate by heat into oxygen and 
potassium chloride is attended with evolution of heat, unlike most cases 
of chemical decomposition, in which heat is .generally absorbed. If the 
chlorate be heated to the point at which it begins to decompose, and a 
little ferric oxide be thrown into it, enough heat will be evolved to bring 
the mass to a red heat, although the ferric oxide is not oxidised. Experi- 
ment has shown that one part of chlorate evolves, during decomposition, 
nearly 39 units of heat, or enough heat to raise 39 parts of water through 
1° C. This anomalous evolution of heat must of course contribute to 
increase the energy of explosive mixtures containing the chlorate, and 
may be accounted for on the supposition that the heat evolved by the 
combination of the potassium with the chlorine to form potassium chloride 
exceeds that which is absorbed in effecting the chemical disintegration of 
the chlorate. 

114. Perchloric acid (HC10 4 ) is obtained by evaporating down, at a 
boiling heat, the solution of chloric acid obtained by decomposing 
potassium chlorate with hydronuosilicic acid (see p. 164), when the 
chloric acid is decomposed into perchloric acid, chlorine, and oxygen ; 
4HC10 3 = 2HC10 4 + H 2 + Cl a + 3 . 

When the greater part of the water has been boiled off, the liquid may be intro- 
duced into a retort and distilled. After the remainder of the water has passed over, 
it is followed by a heavy oily liquid, which is HC10 4 .2H 2 0. If this be mixed with 
four times its volume of strong sulphuric acid and again distilled, the pure per- 
chloric acid (HC10 4 ) first passes over as a yellow watery liquid. If the distillation 
be continued the oily HC10 4 . 2H 2 0, distils over, and if this be mixed with the former 
and cooled, it yields silky crystals containing HC10 4 . H. 2 0, which are decomposed at 
230° F. into HC10 4 , which may be distilled off, ai 
the retort ; 2(HC10 4 . H 2 0) = HC10 4 + HC10 4 . 2H 2 0. 

The pure perchloric acid is a colourless, very heavy liquid (sp. gr. 
1*782), which soon becomes yellow from decomposition. It cannot be 
kept for any length of time. When heated, it undergoes decomposition, 
often with explosion. In its oxidising properties it is more powerful 
than chloric acid. It burns the skin in a very serious manner, and sets 
fire to paper, charcoal, &c, with explosive violence. This want of stability, 
however, belongs only to the pure acid. If water be added to it, heat 
is evolved, and a diluted acid of far greater permanence is obtained. 
Diluted perchloric acid does not even bleach, but reddens litmus in the 
ordinary way. 

Perchloric acid is monobasic. The perchlorates are decomposed by 
heat, evolving oxygen, and leaving chlorides ; thus — KC10 4 = KC1 + 4 . 

The potassium perchlorate is always formed in the lirst stage of 
the decomposition of potassium chlorate by heat; 2KC10 3 = KC10 4 
+ KCl + 2 . 

If a few crystals of potassium chlorate be heated in a test-tube, they first melt to 
a perfectly clear liquid, which soon evolves bubbles of ox} r gen. After a time the 
liquid becomes pasty, and if the contents of the tube, after cooling, be dissolved by 



CHLORIC PEROXIDE. 167 

boiling with water, the latter will deposit, as it cools, crystals of potassium per- 
chlorate. These are readily distinguished from chlorate by their not yielding a yellow 
gas (C10 2 ) when treated with strong sulphuric acid. The perchlorate is remarkable- 
as one of the least soluble of the potassium salts, requiring 150 times its weight of 
cold water to dissolve it. Neither perchloric acid nor any of its salts is applied to* 
any useful purpose. 

115. Chloric peroxide or peroxide of chlorine (C10 2 ) is dangerous to prepare and 
examine on account of its great instability and violently explosive character. It is 
obtained by the action of strong sulphuric acid upon potassium chlorate — 

3KC10 3 + 2H 2 S0 4 = KC10 4 + 2KHS0 4 + 2C10 2 + H 2 0. 

It is a bright yellow gas, with a chlorous and somewhat aromatic smell, and sp. gr. 
2 "32 ; condensible at -4° F. to a red, very explosive liquid. The gas is gradually 
decomposed into its elements by exposure to light, and a temperature of 140° F. 
causes it to decompose with violent explosion into a mixture of chlorine and oxygen, 
the volume of which is one-third greater than that of the compound. 

On a small scale, chloric peroxide may be prepared with safety by pouring a little 
strong sulphuric acid upon one or two crystals of potassium chlorate, in a test-tube 
supported in a holder. The crystals at once acquire a red colour, which gradually 
diffuses itself through the liquid, and the bright yellow gas collects in the tube. If 
heat be applied, the gas will explode, and the colour and odour of chloric peroxide 
will be exchanged for those of chlorine. If the chlorate employed in this experiment 
contains potassium chloride, explosion often takes place in the cold, since the hydro- 
chloric acid evolved by the action of the acid upon that salt decomposes a part of the 
chloric peroxide, and thus provokes the decomposition of the remainder. 

Chloric peroxide is easily absorbed by water, and the solution ha«- 
powerful bleaching properties. Combustible bodies, such as sulphur 
and phosphorus, decompose the gas, as might be expected, with great 
violence. 

This powerful oxidising action of chloric peroxide upon combustible sub- 
stances appears to be the cause of the property possessed by mixtures 
of such substances with potassium chlorate, to inflame when touched with 
strong sulphuric acid. 

If a few crystals of potassium chlorate be thrown into a glass of water (fig. 184), 
one or two small fragments of phosphorus dropped -upon them, and some strong 
sulphuric acid poured down a funnel tube to the bottom of 
the glass, the chloric peroxide will inflame the phosphorus 
with bright flashes of light and slight detonations. 

Powdered sugar mixed with potassium chlorate on paper, 
will burn brilliantly when touched with a glass rod dipped in 
strong sulphuric acid. Matches may be prepared, which 
inflame when moistened with sulphuric acid, by dipping the 
ends of splinters of wood in melted sulphur, and, when cool, 
tipping them with a mixture of 5 grains of sugar and 1 5 grains 
of potassium chlorate made into a paste with 4 drops of water. 
When dry, they may be fired by dipping them into a bottle 
containing asbestos moistened with strong sulphuric acid. 
These matches, under the names of Eupyrion and Vesta 
matches, were used before the introduction of phosphorus into 
general use. The Promethean light was an ornamental scented 
paper spill, one end of which contained a small glass bulb of 
sulphuric acid surrouuded with a mixture of chlorate and 
sugar, which inflamed when the end of the spill was struck Fig. 184. 

or squeezed, so as to break the bulb containing the sulphuric 

acid. The paper was waxed in order to make it inflame more easily. Percussion 
fuzes, &c, have been often constructed upon a similar principle. 

Chloric peroxide used to be called hypochloric acid; but, like nitric 
peroxide, it appears to have no claim to be considered a true acid, since, 
in contact with the alkalies, it yields mixtures of chlo rites and chlorates; 
thus— 2C10 2 + 2KHO = KC10 2 + KC10 3 + H 2 . 




168 



CHLOROUS ACID. 



Euchlorine, the deep yellow, dangerously explosive gas evolved by the 
action of strong hydrochloric acid upon potassium chlorate, appears to 
be a mixture of chloric peroxide with free chlorine. It is resolved by 
explosion into CI and 0, Mercurous chloride absorbs CI from it, 
leaving C10 2 . Hence its production may be explained by the equation, 
4KC10 3 + 12HC1 = 4.KC1 + 6H 2 + 3C10 2 + Cl 9 . 

116. Chlorous anhydride (C1 2 3 )* is another unstable and dangerously 
explosive gas, obtained by the action of a very gentle heat upon a mix- 
ture of 3 parts of white arsenic, 4 of potassium chlorate, and 16 of diluted 
nitric acid (sp. gr. 1 *24) — 
2KC10 3 + 2HN0 3 + As 2 G 3 + 2H 2 = 2KN0 3 + 2H 3 As0 4 + C1 2 3 

Arsenic acid. 

Chlorous anhydride is a deep yellowish-green heavy gas (sp. gr. 2*65) 
which is absorbed by water, and decomposed even more easily than the 
chloric peroxide. The solution is supposed to contain chlorous acid, 



HC10 2 ; for C1 2 3 + H 2 



2HC10 2 , but this has not been obtained in 



the separate state. It is a weak acid, its salts, the chlorites, being decom- 
posed even by carbonic acid. A mixture of ice and salt does not liquefy 
chlorous anhydride, but an intense cold condenses it to a red liquid, of sp. 
gr. 1 "33, which boils at a little above the melting-point of ice, and explodes 
at a somewhat higher temperature. ; 

117. General review of the oxides of chlorine. — Several points of resem- 
blance will have been noticed between the series of oxides of chlorine and 
those of nitrogen, but the former are much less stable than the latter. 
Chlorous anhydride (C1 2 3 ), like nitrous anhydride (N 2 3 ), yields a weak 
acid when dissolved in water ; chloric peroxide (C10 2 ) gives, with alkalies, 
chlorites and chlorates, just as nitric peroxide (N0 2 ) gives nitrites and 
nitrates. Chloric acid (HC10 3 ) is a powerful oxidising agent, like nitric 
acid (HN0 3 ), and the chlorates resemble the nitrates in their solubility in 
water and their oxidising power. The composition by volumes of those 
oxides of chlorine which are known in the separate state is exhibited in 
the following- table : — 



Formula. 


Molecular 
Weight. 


Molecular 
Volume. 


By Volume. 


Hypochlorous anhydride, 
Chlorous ,, 
Chloric peroxide, 


C1 2 

ciA 
cio 2 


87 
119 
67-5 


2 
3 
2 


CI 
2 
2 
1 



1 
3 

2 



Chlorides of Carbon. 

118. It has already been seen that chlorine has no direct attraction for carbon, 
the two elements not being known to enter into direct combination ; but several 
chlorides of carbon may be obtained by the action of chlorine upon other compounds 
of carbon. Thus, if Dutch liquid (C 2 H 4 C1 2 ), produced by the combination of olefiant 
gas with chlorine (p. 96), be acted upon with an excess of chlorine in sunlight, the 
whole of its hydrogen is removed in the form of hydrochloric acid, and an equivalent 
amount of chlorine is substituted for it, yielding the trichloride, formerly called 
sesquichloride of carbon (C 2 C1 6 ) ; C 2 H 4 C1 2 + C1 8 = C 2 C1 6 + 4HC1 . 

* This gas occupies three times the volume of an atom of hydrogen, instead of twice 
that volume, as usual. 



CHLORIDES OF CARBON. 



169 



Carbon trichloride is a white crystalline solid, with an aromatic odour, rather 
like that of camphor. It fuses at 320° F., and boils at 360°, subliming unchanged. 
It is not dissolved by water, but is soluble in alcohol and ether. 

When the vapour of carbon trichloride is passed through a tube containing 
fragments of glass heated to redness, it is decomposed into chlorine and a colourless 
liquid, which is the dichloride, formerly called protochloride of carbon (C 2 C1 4 ). It 
has an aromatic odour, and boils at 248° F. ; is heavier than water (sp. gr. 1*5), 
which does not dissolve it, and is soluble in alcohol and ether. 

By passing the vapour of this carbon dichloride through tubes heated to bright 
redness, it is decomposed into chlorine and monochloride, formerly called subchloride 
of carbon (C 2 C1 2 ), which forms silky crystals almost free from odour, insoluble in 
water, but soluble in ether, and capable of being sublimed unchanged at a high 
temperature. It burns in air with a red smoky flame. 

Carbon tetrachloride (CC1 4 ) lias been mentioned (p. 154) as the final 
result of the action of chlorine upon marsh gas (CH 4 ) and upon chloroform 
(CHC1 3 ). It is easily obtained in large quantity, by passing chlorine 
(dried by passing through a tube containing pumice wetted with strong 
sulphuric acid) (fig. 185) through a bottle containing bisulphide of carbon, 
and afterwards through a porcelain tube wrapped in sheet copper, and 
filled with fragments of broken porcelain, maintained at a red heat by a 
charcoal or gas furnace, and condensing the products in a bottle surrounded 




Fig. 185. — Preparation of carbon tetrachloride. 

by ice. A mixture of carbon tetrachloride and sulphur chloride is thus 
obtained ; CS 2 + Cl 6 = CC1 4 + S 2 C1 2 . By shaking this mixture with potash, 
the sulphur chloride is decomposed and dissolved, whilst the carbon 
tetrachloride separates and falls to the bottom. The upper layer having 
been poured off, the tetrachloride may be purified by distillation. 

Another method of preparing CC1 4 consists in distilling carbon 
disulphide with antimonic chloride. 

Carbon tetrachloride is a colourless liquid, much heavier than water 
(sp. gr. 1-6), having a peculiar odour, and boiling at 172° F. It may be 
solidified at - 9° F. The tetrachloride is insoluble in water, but dissolves 
in alcohol and ether. 

By the action of chlorine on naphthalene (C 10 H 8 ), Laurent obtained, as 
the ultimate result, a crystalline chloride of carbon containing C 10 C1 8 , to 
which he gave the name clilonajplithalise. 



170 



CHLOKIDES OF CARBON. 



It will be noticed that each of the compounds of chlorine with carbon, except the 
trichloride, has its parallel in the compounds of hydrogen with carbon;* thus— 
Acetylene C 2 H 2 corresponds to the monochloride C 2 C1 2 , 
Olefiant gas C 2 H 4 ,, dicliloride C 2 C1 4 , 

Marsh gas CH 4 , , tetrachloride CC1 4 . 

The history of carbon trichloride affords an instructive instance of the influence 
of the molecular weight of a compound upon its properties. By passing the vapour 
of carbon tetrachloride through a tube heated to dull redness, a liquid is obtained 
which is found by analysis to contain precisely the same proportions of carbon and 
chlorine as the solid trichloride above described, but the specific gravity of its vapour 
(H = l) is only 59*25, which is half that of the vapour of solid carbon trichloride, 
showing that in the liquid compound the same proportions of carbon vapour and 
chlorine are condensed into a volume twice as large as in the solid trichloride, and 
it must be represented by the formula CC1 3 . 

The following table exhibits the composition of the chlorides of carbon : — 

Chlorides of Carbon. 





Molecular 
Formulae. 


Molecular 
Volume. 


Molecular 
Weight. 


Monochloride, 


c 2 ci 2 


2 ? 


95'0 


Dicliloride, .... 


C 2 C1 4 


2 


166-0 


Trichloride (solid), . 


C 2 C1 6 


2 


237-0 


(liquid), 


CC1 3 


2 


118-5 


Tetrachloride, 


CC1 4 


2 


154-0 



119. Oxy chloride of carbon, carbonyle chloride, ox phosgene gas, is produced by the 
direct combination of equal volumes of carbonic oxide and chlorine gases under the 
influence of sunlight (whence its last name), when the mixture condenses to half its 
volume of a colourless gas, condensable by cold, having a very peculiar pungent 
smell, and fuming strongly when exposed to moist air, decomposing the moisture 
and producing hydrochloric acid; CO.Cl 2 + H 2 = C0 2 + 2HCl.t It is decomposed 
by alkalies, producing chlorides and carbonates. It is sometimes found useful in 
chemical research for removing hydrogen from organic compounds, and introducing 
carbonic oxide, or its elements, into its place. Its action on ammonia affords an 
example of this- 



4NIL 



CO. CI, 



COH 4 N 2 
Urea. 



Ammonium 
chloride. 



in which two molecules of NH 3 have been decomposed, two atoms of the hydrogen 
having been removed in the form of hydrochloric acid, and replaced by CO. 

COCl 2 may also be prepared by passing a mixture of equal volumes of CO and 
CI through a long tube filled with granulated animal charcoal, which favours the 
combination of the gases ; or by passing dried carbonic oxide through antimony 



120. Silicon tetrachloride, unlike the chlorides of carbon, may be formed 
by the direct union of silicon with chlorine at a high temperature ; but it 
is best prepared by passing dry chlorine over a mixture of silica and 
charcoal, heated to redness in a porcelain tube connected with a receiver 
kept cool by a freezing mixture. Neither carbon nor chlorine separately 
will act upon the silica, but when they are employed together, the 
carbon removes the oxygen and the chlorine combines with the silicon ; 
Si0 2 + C 2 + Cl 4 = SiCl 4 + 2CO, 

* When vapour of carbon dichloride is mixed with hydrogen, and passed through a red 
hot tube, olefiant gas and hydrochloric acid are produced. The tetrachloride, under similar 
circumstances, yields marsh gas. 

f Phosgene gas has also been obtained by heating carbon tetrachloride with phosphoric 
anhydride, in a sealed tube ; 3CCl 4 +P 2 5 =2POCl 3 + 3COCl 2 . 



CHLOEIDE OF NITROGEN. 171 

The tetrachloride is a colourless heavy liquid (sp. gr. 1*52), which 
is volatile (boiling-point, 138° F.), and fumes when exposed to air, the 
moisture of which decomposes it, yielding hydrochloric acid and silica' — 

SiCl 4 + 2H 2 = Si0 2 + 4HC1. 

Although it has received no practical application on a large scale, it is 
valuable to the chemist as a convenient source of compounds of silicon, 
which could not easily be procured from the very unchangeable silica. 

By passing hydrochloric acid over silicon heated to redness, a very remarkable 
liquid is obtained, which is much more volatile than the chloride of silicon (boiling- 
point, 108° F.), and, unlike most chlorine compounds, is inflammable, burning with 
a greenish flame, and producing silica and hydrochloric acid. It fumes strongly in 
air, and is decomposed by water, yielding hydrochloric acid, and the substance termed 
leucone. The composition of this liquid appears to be Si 3 H 4 Cl 10 , and its production 
would be represented by the equation Si 3 + 10HCl = Si 3 H 4 Cl 10 + H 6 . Its decomposi- 
tion by water would be explained by the equation — 

Si 3 H 4 ( „ 
Leucone. 

The boron trichloride (BC1 8 ) is similar in its general character to the 
silicon tetrachloride, and is prepared by a similar process, but it is a gas 
instead of a liquid at ordinary temperatures. 

121. Chloride of nitrogen is the name usually given to the very explo- 
sive compound before referred to as being produced by the action of 
chlorine on sal ammoniac. Its composition is somewhat uncertain ; its 
explosive character rendering its exact analysis very difficult. Some 
chemists regard it as NC1 3 , that is ammonia in which all the hydrogen 
has been displaced by chlorine, whilst others believe it to contain hydrogen, 
regarding it as derived from two molecules- of ammonia (NH 3 .NH 3 ), 
by the substitution of five atoms of chlorine for five of hydrogen (NC1 3 . 
NHCl,). 

It is a yellow, heavy, oily liquid (sp. gr. 1*65), which volatilises easily, 
yielding a vapour of very characteristic odour, which affects the eyes. 
When heated to about 200° F. it explodes with great violence, emitting a 
loud report and a flash of light.* Its instability is, of course, attributable 
to the feeble attraction which holds its elements together ; and the violence 
of the explosion, to the sudden expansion of a small volume of the liquid 
into a large volume of nitrogen, chlorine, and perhaps hydrochloric acid. 
As might be expected, its explosion is at once brought about by contact 
with substances which have an attraction for chlorine, such as phosphorus 
and arsenic ; the oils and fats cause its explosion, probably by virtue of 
their hydrogen; oil of turpentine explodes it with greater certainty than 
the fixed oils. Alkalies also decompose it violently ; whilst acids, having 
no action upon the chlorine, are not so liable to explode it. At 160° F. 
this substance has actually been distilled without explosion. 

Although practically unimportant, the violent explosive properties of 
this substance render it so interesting that it may be well to give some 
directions for its safe preparation. 

Fifty grains of red oxide of mercury are very finely powdered, and thrown into 
a pint bottle of chlorine together with \ oz. (measured) of water. The stopper is 
replaced, and the bottle well shaken, loosening the stopper occasionally, as long as 

* It is said to absorb 38478 gramme-degrees of heat per equivalent, in the process of 
formation, and would therefore disengage that amount of heat in the act of decomposition. 



172 AQUA REG1A. 

the chlorine is absorbed. The solution of hypochlorous acid thus produced is 
filtered from the residual mercuric oxy chloride, and poured into a clean thumb-glass 
(fig. 186). A lump of sal ammoniac weighing 20 grains is then dropped into the 
solution, and the glass is placed under a stout wooden box. After the 
lapse of twenty minutes, the chloride of nitrogen may be exploded by 
inserting through a hole in the box a stick dipped in turpentine, fixed 
at right angles to a longer stick. The glass will be shattered into very 
small fragments. 




122. Aqua regia. — This name has been bestowed upon the 
mixture of 1 measure of nitric, and 3 measures of hydro- 
chloric acid (nitromuriatic acid), which is employed for dis- 
solving gold, platinum, and other metals which are not soluble in the 
separate acids. If a little gold leaf be placed in hydrochloric and nitric 
acids contained in separate glasses, the metal will remain unaffected even 
on warming the acids ; but if the contents of the glasses be mixed, the 
gold will be immediately dissolved by the chlorine, which is liberated in 
the action of the acids upon each other — ■ 

H¥0 3 + 3HC1 = 2H 2 + NOC1 + Cl 2 . 

The nitrosyle chloride (NOC1) is a red gas, condensable in a freezing mixture 
to a dark red liquid, which boils at 18° F. It has a very peculiar odour, and is 
decomposed by contact with water. Nitrosyle chloride is also produced by mixing 
2 volumes of nitric oxide with 1 volume of chlorine ; it condenses to a red liquid at 
0° F. When nitrosyle chloride is passed into oil of vitriol cooled to 32° F., crystals 
of the acid nitrosyle sulphate are deposited ; N0C1 + H. 2 S.0 4 = HC1 + N0HS0 4 . 

BBOMINE. 

Br = 80 parts by weight. 

123. It generally happens that elements between which any strong 
family likeness exists are found associated in nature. This remark par- 
ticularly applies to the three elements — chlorine, bromine, and iodine — all 
of which are found in sea water, though the first predominates to such 
an extent that the others for a long time escaped notice. Bromine was 
brought to light in the year 1826 by Balard in the examination of bittern, 
which is the liquid remaining after the sodium chloride and some other 
salts have been made to crystallise by evaporing sea water, which contains 
only about 1 grain of bromine per gallon in the forms of bromide of 
magnesium and bromide of sodium. It is also extracted from the waters 
of certain mineral springs, as those of Kreuznach and Kissingen, which 
contain much larger quantities of bromine, combined with potassium, 
sodium, or magnesium. During the last few years much bromine has 
been obtained from the mother-liquors of the salt-works at Stassfurth, 
and from saline springs in the United States. 

In extracting the bromine from these waters, advantage is taken of the 
circumstance that chlorine is capable of displacing bromine from its 
combinations with the metals. After most of the other salts, such as 
sodium chloride, sodium sulphate, and magnesium sulphate, which are 
less soluble than the bromides, have been separated from the water 
by evaporation and crystallisation, the remaining liquid is subjected to the 
action of chlorine gas, when it acquires an orange colour, due to the 
liberation of the bromine; KBr + C1 = KC1 + Br. The bromine thus 
set free exists now diffused through a large volume of water, which can- 
not be separated from it in the usual way, by evaporation, because bromine 
is itself very volatile. An ingenious expedient is therefore resorted to, of 



EXTRACTION OF BROMINE. 173 

shaking the orange liquid briskly with ether, which has a greater solvent 
power for bromine than is possessed by water, and therefore abstracts it 
from the aqueous solution : since ether does not mix to any great extent 
with water, it now rises to the surface of the liquid, forming a layer of a 
beautiful orange colour, due to the bromine which it holds in solution. 
This orange layer is carefully separated, and shaken with solution of 
potash, which immediately destroys the colour by removing the bromine, 
leaving the ether to rise to the surface in a pure state, and fit to be 
employed for abstracting the bromine from a fresh portion of the water. 
The action of the bromine upon potash is precisely similar to that of 
chlorine; 6KHO + Br 6 = 5KBr + KBr0 3 + 3H 2 0. 

Potassium Potassium 
bromide. bromate. 

After the solution of potash has been several times shaken with the 
ethereal solution of bromine, and has become highly charged with this 
element, it is evaporated so as to expel the water, leaving a solid residue 
containing the potassium bromide and bromate. This saline mass is 
strongly heated to decompose the bromate, and convert it into bromide ; 
KB1O3 = KBr + 3 . 

From this salt the bromine is extracted by distilling it with manganese 
dioxide and sulphuric acid, when the potassium is oxidised at the expense 
of the manganese dioxide, and the bromine is liberated and condensed in a 
receiver kept cold by iced water — 

2KBr + Mn0 2 + 2H 2 S0 4 = K 2 S0 4 + MnS0 4 + 2H 2 -f Br 2 . 

The aspect of the bromine so produced is totally diffierent from that of 
any other element, for it distils over in the liquid condition, and 
preserves that form at ordinary temperatures, being the only liquid non- 
metallic element. Its dark red-brown colour, and the peculiar orange 
colour of the vapour which it exhales continually, are also characteristic ; 
but, above all, its extraordinary and disagreeable odour, from which it 
derives its name (/?/o6j/xos, a stench), leaves no doubt of its identity. The 
odour has some slight resemblance to that of chlorine, but is far more 
intolerable, often giving rise to great pain, and sometimes even to breeding 
at the nose. 

Liquid bromine is thrice as heavy as water (sp. gr. 2 '96), and boils at 
63° C, yielding a vapour 5J times as heavy as air (sp. gr. 5*54). It 
may be frozen at - 7° C. to a brown crystalline solid. It requires 33 
times its weight of cold water to dissolve it, and is capable of forming a 
crystalline hydrate (Br. 5H 2 0) corresponding to chlorine hydrate. 

In its bleaching power, its aptitude for direct combination, and its 
other chemical characters, it very closely resembles chlorine, so closely, 
indeed, that it is difficult to distinguish, in many cases, between the com- 
pounds of chlorine and bromine with other substances, unless the elements 
themselves be isolated. A necessary consequence of so great a similarity 
is, that very little use has been made of bromine, since the far more 
abundant chlorine fulfils nearly all the purposes to which bromine might 
otherwise be applied. In the daguerreotype and photographic arts, how- 
ever, some special applications of bromine have been discovered, and for 
some chemical operations, such as the determination of the illuminating 
hydrocarbons in coal gas, bromine is sometimes preferred to chlorine. It 
has also been used in America as a disinfectant. The bromides of potas- 
sium and ammonium are frequently employed in medicine. Bromide of 



174 



HYDROBROMIC ACID. 



cadmium is used in photography. In the composition of their compounds 
chlorine and bromine exhibit great analogy. 

Hypobromous acid (HBrO) has been obtained in solution by shaking- 
mercuric oxide with water and bromine. The solution is very unstable, 
decomposing, especially when heated, with liberation of bromine and for- 
mation of bromic acid. The action of bromine upon diluted solutions of 
the alkalies, and upon the alkaline earths, produces bleaching liquids 
similiar to those formed by chlorine. 

Bromic acid (HBr0 3 ) can be prepared in a similar manner to chloric 
acid, to which it has a great general resemblance, the bromates being also 
similar to the chlorates. 

124. Hydrobromic acid (HBr = 81 parts by weight = 2 volumes). — 
The inferiority of bromine to chlorine in chemical energy is well exemplified 
in its relations to hydrogen ; for the vapour of bromine mixed with hydro- 
gen will not explode under the action of flame or of the electric spark, 
like the mixture of chlorine and hydrogen. Direct combination may, 
however, be slowly induced by contact with heated platinum. 

When it is attempted to prepare this acid by distilling bromide of 
sodium or potassium with sulphuric acid (as in the preparation of hydro- 
chloric acid) the inferior stability of hydrobromic acid is shown by the 
decomposition of a part of it, the hydrogen being oxidised by the sulphuric 
acid, and the bromine set free ; 2 HBr + H 2 S0 4 = 2H 2 + S0 2 + Br 2 . 

If a strong solution of phosphoric acid be employed instead of the 
sulphuric, pure hydrobromic acid may be obtained. 

But the most instructive method of obtaining 
hydrobomic acid consists in attacking water 
with bromine and phosphorus simultaneously, 
when the phosphorus takes the oxygen of the 
water, forming phosphoric acid, and the 
bromine combines with the hydrogen to form 
hydrobromic acid— 

3H 2 + Br 5 + P = HP0 3 4 5HBr 

Phosphoric acid. 
The experiment may be made in a W-formed tube 
(fig. 187), one bend of which contains 40 grains of 
phosphorus in fragments intermingled with glass 
moistened with water, whilst the other bend contains 
240 grains of bromine (about 1 drachm). This limb of the tube is corked, and the 
other furnished with a delivery tube, so that the gas may be collected either by 
downward displacement or over mercury. The bromine is slightly heated, when it 
distils over to the moist phosphorus, and hydrobromic acid is evolved. A moderate 
heat should afterwards be applied to the moist glass, to expel part of the hydrobromic 
acid from the water. 

Hydrobromic acid is very similar to hydrochloric acid ; it liquefies at 
- 92° F., and has been solidified by a still lower temperature, which is not 
the case with hydrochloric acid. Like that gas, it is very soluble in water, 
and the solution acts upon metals and their oxides in the same manner 
as hydrochloric acid. Chlorine removes the hydrogen from hydrobromic 
acid, liberating bromine, which it converts into chloride of bromine if 
employed in excess. 

Bromide of nitrogen has been obtained by the action of bromide of 
potassium upon chloride of nitrogen, which it resembles in gener 
character and explosive properties. 




Fig. 187. — Preparation of 
hydrobromic acid. 



DISCOVERY OF IODINE. 175 

Carbon tetrabromide, CBr 4 , is obtained by beating CC1 4 witb aluminium 
bromide in a sealed tube to 100° C. 

Chloride of bromine is a very volatile yellow liquid of pungent odour. 
Its composition is not certainly known. Tbat chlorine should unite 
directly with bromine, which it so much resembles in chemical character, 
illustrates its great tendency to direct chemical combination. 

IODINE. 

1 = 127 parts by weight. 

125. Iodine is contained in sea water in even smaller quantity than 
bromine, but the sodium iodide appears to constitute a portion of the 
necessary food of certain varieties of sea-weed, which extract it from the 
sea water, and concentrate it in their tissues. The ash remaining after 
sea- weed has been burnt was long used, under the name of kelp, in soap- 
making, because it contains a considerable quantity of sodium carbonate ; 
and in the year 1811, Courtois, a soap-boiler of Paris, being engaged in 
the manufacture of soda from kelp, obtained from the waste liquors a 
substance which possessed properties different from those of any form of 
matter with which he was acquainted. He transferred it to a French 
chemist, Clement, who satisfied himself that it was really a new substance ; 
and Gay-Lussac and Davy having examined it still more closely, it took 
its rank among the non-metallic elementary substances, under the name 
of iodine (twS^s, violet-coloured,), conferred upon it in allusion to the 
magnificent violet colour of its vapour. 

This history of the discovery of iodine affords a very instructive example 
of the advantage of training persons engaged in manufactures to habits of 
accurate observation, and, if possible, of accurate chemical observation; 
for had Courtois passed over this new substance as accidental, or of no 
consequence, the community would have lost, at least for some time, the 
benefits derived from the discovery of iodine. 

For some years the new element was only known as a chemical 
curiosity, but an unexpected demand for it at length arose on the part of 
the physician, for it had been found that the efficacy of the ashes of 
sponge, which had long been used in some particular maladies, was due 
to the small quantity of iodine which they contained, and it was of course 
thought desirable to place this remedy in the hands of the medical pro- 
fession in a purer form than the ash of sponge, where it is associated with 
very large quantities of various saline substances. Much more recently, 
the demand for this element has greatly increased on account of its employ- 
ment in photography, and large quantities of it are annually produced 
from kelp, the collection and burning of which affords occupation to the 
very poor inhabitants of some parts of the coasts of Ireland and Scotland, 
who would otherwise have been thrown out of work when soda began to 
be manufactured from common salt, and the demand for kelp as the source 
of that alkali had ceased. The sea-weed* is spread out to dry, and burnt 
in shallow pits at as low a temperature as possible; for the sodium iodide 
is converted into vapour and lost if the temperature be very high. The 
ash, which is left in a half-fused state, is broken into fragments and 
treated with hot water, which dissolves about half of it, leaving a residue 
consisting of calcium carbonate and sulphate, sand, &c. The whole of the 

* The Laminaria digitata, or deep sea tangle, contains most iodine. 



176 



EXTRACTION OF IODINE. 



sodium iodide is contained in the portion dissolved by the water, but is 
mixed with much larger quantities of sulphate, carbonate, hyposulphite, 
sulphide and bromide of sodium, together with sulphate and chloride of 
potassium. A portion of the water is expelled by evaporation, when the 
sulphate and carbonate of sodium and chloride of potassium, being far less 
soluble than the iodide of sodium, crystallise out. In order to decompose the 

hyposulphite and sulphide 
of sodium, the liquid is 
mixed with an eighth of its 
bulk of oil of vitriol, which 
decomposes these salts, 
evolving sulphurous and 
hydrosulphuric acid gases, 
with deposition of sulphur, 
and forming sodium sul- 
phate, which is deposited in 
crystals. The liquor thus 
prepared is next mixed with 
manganese dioxide, and 
heated in an iron still 
with a leaden cover (fig. 
188), when the iodine is 
evolved as a magnificent 
purple vapour, which con- 
denses in the globular glass 
or stoneware receivers in the form of dark grey scales with metallic lustre, 
and having considerable resemblance to black lead. The liberation of the 
iodine is explained by the following equation — 2NaI + Mn0 2 + 2H 2 SO, 
= ¥a 2 S0 4 + MnS0 4 + 2H 2 + 1 2 . 

When no more iodine passes over, some more manganese dioxide is 
added, and the bromine then distils. The quantity of bromine obtained 
is about one-tenth that of the iodine. 




Fig. 188. — "Extraction of iodine. 



Several processes have been devised to render the extraction of the iodine from the 
concentrated solution of kelp easier and more economical. The most promising is 
very similar to that employed for ., separating bromine (p. 172). The iodine is 
liberated by chlorine, and extracted from the liquid by shaking it with benzene ; by 
treating the benzene with solution of potash, the iodine is converted into a mixture 
of potassium iodide and iodate, from which the iodine may be precipitated 
by acidifying with hydrochloric acid — 6KHO + I 6 = 5KI + KI0 3 + 3H 2 ; 
5kl + KIO 3 + 6H0I = 6KCl + 3H 2 O + I 6 . A far more economical process for the 
treatment of sea-weed consists in distilling it, when ammonia, acetic acid, naphtha, 
tar, and illuminating gas are obtained, whilst a porous charcoal remains in the retort, 
which is treated with water in order to extract the iodides and other soluble salts. 
This charcoal somewhat resembles animal charcoal in character, containing much 
phosphate and carbonate of calcium and magnesium; it is useful as a decolorising 
and deodorising agent. Iodine is now extracted from the deposits of nitrate of soda 
occurring in Chili, which contain sodium iodate (NaI0 3 ). 

The features of this element are extremely well marked : its metallic 
lustre and peculiar odour sufficiently distinguish it from all others, and 
the effect of heat upon it is very striking, in first easily fusing it (at 225° 
F.), and afterwards converting it (boiling-jooint, 347° E.) into the most 
exquisitely purple vapour, which is nearly nine times as heavy as air (sp. 
gr. 8*72), and condenses upon a cool surface in shining scales. It stains 



PEOPEETIES OF IODINE. 177 

the skin intensely brown if handled. The specific gravity of solid iodine 
is 4-95. 

When iodine is shaken with cold water, a very small quantity is dis- 
solved, forming a light brown solution. Hot water dissolves a larger 
quantity, but alcohol is one of the best solvents for iodine, producing a 
dark red-brown solution from which part of the iodine may be precipi- 
tated by adding water. A solution of potassium iodide also dissolves 
iodine freely (JLugoVs solution ; liquor iodi). Tincture of iodine contains 
iodine with half its weight of potassium iodide dissolved in alcohol. 
Benzene and carbon disulphide dissolve it abundantly, producing fine 
violet-red solutions, which deposit the iodine, if allowed to evaporate 
spontaneously, in minute rhombic octahedral crystals aggregated into very 
beautiful fern-like forms. If an extremely weak aqueous solution of 
iodine be shaken with a little carbon disulphide, the latter will remove 
the iodine from the solution, and on standing, will fall to the bottom of 
the liquid, having a beautiful red colour. By dissolving a large quantity 
of iodine in carbon disulphide, a solution is obtained which is perfectly 
opaque to rays of light, though it allows heat- rays to pass freely, and is 
therefore of great value in physical experiments. A solution of iodine in 
carbon tetrachloride is also used for the same purpose. 

Existing, as iodine does, in very minute quantity in the water from 
various natural sources, it would often be overlooked if the chemical 
analyst did not happen to possess a test of the most delicate description 
for it. 

Iodine, in the uncombined state, dyes starch of a beautiful blue colour, 
as may be proved by heating a grain or two of the element with water, 
and adding to the cold solution a little thin starch (see p. 55), or by 
placing a minute fragment of iodine in a stoppered bottle, and suspend- 
ing in it a piece of paper dipped in thin starch. This test, however, 
though sensitive to the smallest quantity of free iodine, gives no indica- 
tion whatever with iodine in combination, as it always exists in nature; 
in order, therefore, to test for iodine, a little starch-paste is added to the 
suspected liquid, and then a drop of a weak solution of chlorine, which 
will set free the iodine, and cause the production of. the blue colour. It 
is necessary, however, carefully to avoid adding too much chlorine, since 
it would immediately destroy the colour of the iodised starch. If, then, 
a very little sulphurous acid be added, the blue tint returns, and is again 
bleached by more sulphurous acid.* Alkalies also bleach it, and the 
colour of a mixture of the iodised starch with water is removed by heat- 
ing, but returns in great measure when the solution cools. The starch 
appears to be only , dyed by the iodine, and not combined with it ; on 
snaking the blue iodised starch for some time with CS 2 , the blue colour 
is removed, and the red solution of iodine in CS 2 is obtained. 

Though very closely connected with chlorine and bromine in its general 
chemical relations, there are several points in the history of iodine which 
cause it to stand out in marked contrast by the side of these elements. 
The attraction which binds it to hydrogen and the metals is certainly 
weaker than that exerted by chlorine and bromine, so that either of these 
is capable of displacing it from its compounds, and its bleaching properties 

* The following equations explain these changes : — 

(1) KI + C1=KCI + I; (2) I + 3H 2 + C1 5 =HI0 3 + 5HC1; 

(3) 2HI0 3 + 5H 2 S0 3 =5H 2 S0 4 +I 2 + H 2 0; (4) I 2 + H 2 + H 2 S0 3 =2HI + H 2 S0 4 . 

M 



178 IODIC ACID. 

are very feeble. On the other hand, it exhibits a more powerful tendency 
to unite with oxygen ; for boiling nitric acid converts it into iodic acid 
(HI0 3 ), though this oxidising agent would not affect chlorine or bromine. 

Some of the compounds of iodine with the metals are remarkable for their beautiful 
colours. The mercuric iodide, produced by mixing solutions of potassium iodide and 
mercuric chloride, forms a fine scarlet precipitate, which dissolves in an excess of 
potassium iodide to a colourless solution. 

If the mercuric iodide be collected on a filter, washed and dried, it will be found, 
on heating a portion of it in a test-tube, that it acquires a fine yellow colour, and 
sublimes in golden yellow crystals, which resume the original red colour when rubbed 
with a glass rod. If it be spread upon paper and gently heated, the scarlet iodide 
becomes yellow, but the red colour returns on rubbing it with the thumb-nail. These 
changes of colour are attended by an alteration in crystalline form, but not in the 
chemical composition of the mercuric iodide. This iodide is used in painting under 
the name of pure scarlet or iodine scarlet, but the colour is not durable. 

Lead iodide has a bright yellow colour, as may be seen by precipitating potassium 
iodide with a solution of lead acetate. The precipitate is dissolved by boiling with 
water (especially on adding a little hydrochloric acid), forming a colourless solution, 
from which the lead iodide crystallises in very brilliant golden scales on cooling. 
Silver iodide is produced, as a yellow precipitate when silver nitrate is added to 
potassium iodide. The bromide and chloride of silver would form white precipi- 
tates. Silver iodide is more stable than the chloride or bromide ; when ex- 
posed to light it appears to be unchanged, but if a reducing agent, such as ferrous 
sulphate or pyrogallin, be afterwards poured over it, that portion of the iodide which 
has been exposed to light is immediately blackened, from the separation of silver in 
the metallic state. This is the principle of the process for developing the negative 
photograph taken on a collodion film rendered sensitive by silver iodide. The 
iodides of potassium, ammonium, and cadmium are also used in photography. 

126. Iodic acid, HI0 3 . — It is most easily prepared by boiling iodine 
with the strongest nitric acid in a long-necked flask, when it is dissolved 
in the form of iodic acid, which is left, on evaporating the nitric acid, as 
a white mass. This may be purified by dissolving in water and crystal- 
lising, when the iodic acid forms white hexagonal tables, which have the 
composition HI0 3 .Aq. Heated to 266° F. they become HI0 3 , and at 
360° F. the iodic acid is decomposed into water and iodic anhydride, 
2HI0 3 = H 2 + I 2 5 . This last is decomposed at about 700° F. into 
iodine and oxygen. The iodic anhydride oxidises combustible bodies, 
but not with any great violence. The acid is far more stable than 
chloric and bromic acids. Its solution first reddens litmus paper, and 
afterwards bleaches it by oxidation. Its salts, the iodates. are less 
easily soluble in water than the chlorates and bromates, which they 
resemble in their oxidising action upon combustible bodies. They 
are all decomposed by heat, evolving oxygen, and sometimes even iodine, 
showing how much inferior this element is to chlorine and bromine 
in its attraction for metals. The iodates exhibit some remarkable irregu- 
larities in their composition. 

Periodic acid, HI0 4 , is obtained from the basic sodium periodate formed bypassing 
chlorine through a mixture of sodium iodate and sodium hydrate, when the latter is 
decomposed, its sodium being abstracted by the chlorine, whilst its oxygen converts 
the iodic acid into periodic acid ; NaI0 3 + 3NaHO + Cl 2 = 2NaCl + NaI0 4 .NaHO.H 2 
(basic sodium periodate). 

This periodate is deposited, being sparingly soluble in water, a most unusual 
circumstance with sodium salts. By dissolving it in nitric acid, and adding silver 
nitrate, a basic silver periodate is obtained, which is yellow when precipitated from 
cold, and red from hot solutions. "When the silver salt is dissolved in nitric acid, it 
is decomposed into silver nitrate, which remains in solution, and normal silver 
periodate, AgI0 4 , which is deposited in crystals. When this is boiled with water, 



HYDRIODIC ACID. 



179 



it again yields the insoluble basic periodate, and periodic acid is found in the solu- 
tion. On evaporating the solution, the periodic acid is deposited in prismatic 
crystals having the composition HI0 4 .2Aq, which are decomposed at about 320° F., 
2HI0 4 .2Aq = I 2 7 + 3H 2 0. The I 2 7 is decomposed into I 2 5 and 2 at 400° F. 
The solution of periodic acid, of course, exhibits oxidising properties. 

The perioclates are remarkable for their sparing solubility in water. : they are easily 
decomposed by heat, like the iodates. It will have been remarked in the above 
account of the preparation of periodic acid, that this acid exhibits a great tendency 
to the formation of basic salts, whilst iodic acid is remarkable for its acid salts. 

127. Hydriodic acid (HI =128 parts by weight = 2 volumes). — Iodine 
vapour combines with hydrogen, under the influence of heated platinum, 
to form hydriodic acid gas. The gas is best prepared by decomposing 
water with, iodine in the presence of phosphorus; 6H 2 + I 6 + P Q = 6HI 
+ 2H 3 P0 3 . 

100 grains of potassium iodide are dissolved in 50 grains of water in a retort (fig. 
189), and 200 grains of iodine are added ; Avhen this has dissolved, 10 grains of 
amorphous phosphorus are introduced, and the 
mixture heated very gradually, the gas being 
collected by downward displacement in stop- 
pered bottles, which must be placed in readiness, 
as the gas comes off very rapidly. These 
quantities will fill four pint bottles with the gas. 




189. — Preparation of 
hydriodic acid. 



Hydriodic acid gas is very similar in 
its properties to hydrochloric and hydro- 
bromic acids, fuming strongly in moist 
air, very readily absorbed by water, 
liquefied only under strong pressure, and 
solidified by extreme cold. It is much 
heavier, its specific gravity being 4 - 44. 
If a bottle of hydriodic acid gas be placed in contact with a bottle con- 
taining chlorine or bromine vapour diluted with air (fig. 148) it will be 
instantly decomposed, with separation of the beautiful violet vapour of 
iodine. 

The aqueous solution of hydriodic acid is most conveniently prepared 
by passing hydrosulphuric acid gas through water in which iodine is 
suspended, H 2 S + I 2 = 2HI + S, the separated sulphur being filtered off, 
and the solution boiled to expel the excess of hydrosulphuric acid.' 55 ' 
Solution of hydriodic acid differs greatly from hydrochloric and hydro- 
bromic acids, in being decomposed by exposure to air, its hydrogen being 
oxidised and iodine separated, which dissolves in the liquid, and renders 
it brown. 

This tendency of the hydrogen of hydriodic acid to combine with 
oxygen renders that acid a powerful reducing agent. It is even capable 
of converting sulphuric acid into hydrosulphuric acid — 

H 2 S0 4 + 8HI = H 2 S + 4H 2 + 1 8 , 

so that when potassium iodide is heated with concentrated sulphuric acid, 
hydrosulphuric acid is evolved in considerable quantity. 

The action of hydriodic acid upon the metals and their oxides is gene- 
rally similar to that of the other hydrogen acids. 

In organic chemistry, hydriodic acid is often employed for removing 
oxygen and replacing it by hydrogen. 

When potassium is heated in a measured volume of hydriodic acid, 



Strong solution of hydriodic acid is able to convert sulphur into hydrosulphuric acid. 



180 POTASSIUM IODIDE. 

the iodine is removed, and the hydrogen occupies half the original volume. 
Hence 1 volume of hydrogen is combined with 1 volume of iodine vapour 
in 2 volumes of hydriodic acid. 

Like chlorine and bromine, iodine is capable of displacing hydrogen 
from many organic compounds, and of taking its place ; but its action in 
this respect is much feebler. The circumstance that the organic com- 
pounds containing iodine are generally much less volatile, and therefore 
more manageable, than those of chlorine and bromine, leads to the ex- 
tensive employment of this element in researches upon organic substances. 

With olefiant gas, iodine forms a crystalline solid compound (C 2 H 4 I 2 ) 
corresponding to Dutch liquid (p.. 96). 

Carbon tetra-iodide, CI 4 , is obtained by decomposing carbon tetrachloride 
with aluminium iodide, in presence of carbon disulphide. It forms octa- 
hedral crystals which are very unstable. 

128. Iodide of nitrogen. — The action of chlorine, bromine, and iodine 
upon ammonia exemplifies the difference in their attraction for hydrogen; 
for whilst chlorine and bromine, acting upon ammonia, cause the libera- 
tion of a certain amount of nitrogen, iodine simply removes two-thirds of 
the hydrogen, and itself fills up the vacancies thus occasioned, no nitrogen 
being liberated, NH 3 + 1 4 = NHI 2 + 2HI, the hydriodic acid thus formed 
combining with more ammonia to form ammonium iodide. 

To prepare the iodide of nitrogen, 20 grains of iodine are rubbed to powder in a 
mortar and mixed with half an ounce (measured) of strong ammonia : the mortar 
is covered with a glass plate, and after about half an hour the iodide of nitrogen is 
collected in separate portions upon four filters, which are allowed to drain and 
spread out to dry. The brown solution contains iodine dissolved in ammonium 
iodide. 

Another method consists in dissolving iodine in a mixture of hydrochloric with 
a little nitric acid, with the aid of heat, and adding ammonia, which decomposes 
the IC1 in solution, and gives a black precipitate of the iodide of nitrogen. 

The iodide is a black powder, which explodes with a loud report even 
when touched with a feather, emitting fumes of hydriodic acid and 
purple vapour of iodine : its explosion is probably represented by the 
equation — 

NHI 2 = N + HI + I, 
its violence being accounted for by the sudden evolution of a large volume 
of gas and vapour from a small volume of solid. Even when allowed to 
fall from the height of a few feet upon the surface of water, it explodes 
if perfectly dry. In the moist state it slowly undergoes decomposition. 

When dry NH 3 gas is passed over iodine cooled by ice, iodammonium 
iodide (NH 3 I) I is produced. 

129. Iodine forms two compounds with chlorine, monochloride (IC1) 
and trichloride (IC1 3 ). The former is obtained by distilling 1 part of 
iodine with 4 parts of potassium chlorate. It fuses at 76° F., and boils 
at 214° F. 

The trichloride forms fine red needle-like crystals, and is produced 
when iodine is acted upon with an excess of chlorine. Bromides of iodine 
have also been obtained, but their composition is not well known. 

130. Potassium iodide (KT = 166 parts by weight). — This salt is the 
most useful compound of iodine, being largely employed in medicine and 
in photography. It is generally prepared by decomposing ferrous iodide 
with potassium carbonate. 



IODIDE OF POTASSIUM — FLUOEINE. 181 

The iodide of iron or ferrous iodide (also a useful medicine) is made 
by placing 2 parts of iodine in contact with 1 part of iron filings and 10 
parts of water. The iodine combines with part of the iron, evolving con- 
siderable heat, and producing FeL, . 

The liquid is decanted from the excess of iron, and one-third of the 
weight of iodine previously employed is dissolved in it. In this way two- 
thirds of the ferrous iodide are converted into ferric iodide (Fe 2 I 6 ), so 
that the solution contains a mixture of one molecule of Fel 2 and one of 
Fe 2 I 6 . It is now boiled, and potassium carbonate is gradually added as 
long as it causes a dark green precipitate of magnetic oxide of iron, Fel 2 
+ Fe 2 I 6 + 4K 2 C0 3 = 8KI + FeO.Fe 2 3 + 4C0 2 , the carbonic acid gas is 
evolved with effervescence, and if the solution be filtered and evaporated, 
it deposits beautiful cubical (or sometimes octahedral) crystals, which are 
generally milk-white and opaque, but occasionally quite transparent. 
Pure potassium iodide remains dry in ordinary air ; but if an excess of 
potassium carbonate is employed in its preparation, the crystals retain 
some of that salt, and become damp when exposed to air. The potassium 
iodide dissolves easily in water and alcohol. If the solution be pure, it 
does not become coloured when mixed with pure hydrochloric acid ; but 
if any potassium iodate be present in it, a brownish colour will be pro- 
duced, due to iodine liberated in the action of the iodic acid upon the 
hydriodic acid; HI0 3 + 5HI = 3H 2 + 1 6 . The iodate is liable to be 
present in those specimens which are prepared by dissolving iodine in 
potash, to obtain a mixture of iodide and iodate of potassium, the latter 
salt being afterwards decomposed by heat. # 

By saturating solution of potassium iodide with iodine, G. S. Johnson 
obtained fine crystals of potassium tri-iodide (KI 3 ). Ammonium tri- 
iodide, NH 4 I 3 , was obtained in a similar way. 

FLUORINE. 

F = 19 parts by weight. 

131. The most ornamental mineral substance occurring in any abund- 
ance in this country is known as Jiuor spar or Derbyshire spar (fluoride 
of calcium), and is found with several beautiful shades of colour — blue, 
purple, violet, or green, and sometimes perfectly colourless, either in large 
masses or in crystals, which have the form of a cube or of some solid 
derived from it. The use of this mineral as a flux in smelting ores dates 
from a very remote period, and from this use the name fluor appears to 
have been originally derived ; but we have no record of its chemical ex- 
amination till about a century since, when Margraf found his glass retort 
powerfully corroded in distilling this mineral with sulphuric acid, and 
Scheele soon after announced that it contained lime and fluoric acid. 
But though this chemist had fallen into the error to which analysts are 
continually liable, of mistaking products for educts, his experiments, as 
they were afterwards perfected by Gay-Lussac and Thenard, deserve par- 
ticular consideration. 

132. Hydrofluoric acid (HF = 20 parts by weight = 2 volumes).* — If 
powdered fluor spar be mixed with twice its weight of oil of vitriol, and 

* From some determinations of the specific gravity of the vapour at low temperatures, 
Mallet considers the molecule to be H 2 F 2 =40, and to undergo dissociation into 2HF at 
temperatures approaching 100° C. 



182 



HYDKOFLUORIC ACID. 



heated in a leaden retort (fig. 190), the neck of which fits tightly into a 
leaden condmsing-tube, cooled in a mixture of ice and salt, a colourless 
liquid distils over, and the residue in the retort is found to consist of 
calcium sulphate* — 



CaK + 



H 2 S0 4 



= CaSO A + 2HF. 




Fig. 190. 



The colourless liquid (hydrofluoric acid) possesses most remarkable pro- 
perties : it is powerfully acid, fumes strongly in the air, and has a most 

pungent irritating odour. If the air is at 
all warm, the liquid begins to boil when 
taken out of the freezing mixture. Should 
the operator have the misfortune to allow 
a drop to fall upon his hand, it will 
produce a very painful sore, even its 
vapour producing pain under the finger 
nails. Its attraction for water is so great, 
that the acid hisses like red hot iron when 
brought in contact with it. But its most 
surprising property is that of rapidly 
corroding glass, which has already been 
alluded to as noticed by Margraf. Experiment soon proved that great 
analogy existed between the properties of this new acid and those of 
hydrochloric acid ; and Ampere was led to institute a comparison between 
them, which caused him to adopt the opinion that the acid was a 
hydrogen-acid, containing a new salt radical, which he named fluorine : 
the name of the acid was then changed from fluoric to hydrofluoric acid. 

This liquid has since been proved to be a solution of hydrofluoric acid 
in water ; for if it be distilled with phosphoric anhydride, which retains 
the water, it evolves hydrofluoric acid gas, which resembles hydrochloric 
acid gas in fuming strongly on contact with moist air and being eagerly 
absorbed by water, but has a far more pungent odour. The perfectly 
dry gas has very little action upon glass. 

Pure hydrofluoric acid is prepared by heating dry potassium hydro- 
fiuate (KHF 2 ) to redness in a platinum still. It is then obtained as a 
colourless liquid, which boils at 67° R, and has the specific gravity 
0-988 at 55° F. The pure acid scarcely affects metals, excepting potas- 
sium and sodium. It corrodes glass, however, rapidly, though its vapour 
has little action on glass unless moisture is present. It combines eagerly 
with sulphuric and phosphoric anhydrides, with great evolution of heat, 
a circumstance in which it resembles water, and differs altogether from 
its more obvious analogue, hydrochloric acid. It is also found that it 
combines energetically with the fluorides of potassium and sodium, pre- 
cisely as water combines with the oxides of those metals, whilst nothing 
of the kind is noticed in the case of hydrochloric acid. 

It is remarkable that the solution of hydrofluoric acid, in its concen- 
trated form, is not so heavy as a somewhat weaker acid. Thus the acid 
of sp. gr. 1*06 acquires the sp. gr. 1*15 on addition of a little water ; but 
on adding more water, its sp. gr. is again reduced. It would hence 
appear that the acid of 1*15 is a definite hydrate of hydrofluoric acid : its 



* The mineral kryolite (fluoride of aluminium and sodium) may be advantageously sub- 
stituted for fluor spar, being more easily obtained in a pure state. For preparing the acid 
on a large scale, iron retorts are employed. 



HYDROFLUORIC ACID. 183 

composition corresponds to HF.2H 2 0. It distils unchanged at 248° F. 
The solution is generally kept in bottles made of gutta-percha. 

The action of hydrofluoric acid upon metals and their oxides resembles 
that of hydrochloric acid. It dissolves all ordinary metals except gold, 
platinum, silver, mercury, and lead. Strange to say, it has but little 
action on magnesium. 

The property which renders this acid so useful to the chemist is its 
power of dissolving silica even in its most refractory form. When sand 
or flint reduced to powder is digested in a leaden or platinum vessel 
with hydrofluoric acid, it is gradually dissolved; and if the solution 
be evaporated, the whole of the silica will be found to have disappeared 
in the form of gaseous silicon tetrafluoride ; Si0 2 + 4HF = SiF 4 + 2H 2 0. 
If the silica be combined with a base, the metal will be left as a fluoride, 
decomposable by sulphuric or hydrochloric acid. This renders hydro- 
fluoric acid a most valuable agent in the analysis of the numerous mineral 
silicates which resist the action of other acids. 

The corrosion of glass by hydrofluoric acid is now easily explained. 
Ordinary glass consists of silicate of sodium or potassium combined with 
silicate of calcium or lead. The hydrofluoric acid attacks and removes 
the silica, and thus eats its way into the glass. 

In order to demonstrate the action of this acid upon glass, a glass plate is warmed 
sufficiently to melt wax, a piece of which is then rubbed over it, until the glass is 
covered with a thin and pretty uniform coating. Upon this a word or drawing may 
be engraved with a sharp point so that the lines shall expose the glass. A mixture 
of powdered fiuor spar with concentrated sulphuric acid is then poured over it, and 
allowed to remain for a quarter of an hour : the acid mixture is washed off, and the 
plate gently warmed to melt the wax, which may be wiped off with a little tow, 
when it will be found that the hydrofiuoi'ic acid evolved from the mixture has cor- 
roded those portions of the glass from which the graver had removed the wax. It 
has been attempted to apply this process to the production of engravings, but the 
brittleness of the plate has formed a very serious obstacle. 

If a leaden or platinum dish be at hand, it is better to place the glass to be etched 
over the dish containing the mixture of fiuor spar and sulphuric acid exposed to a 
very gentle heat. 

The solution of hydrofluoric acid etches glass without deadening the 
surface, as is the case with the vapour ; but a solution of fluoride of 
potassium or ammonium mixed with sulphuric acid does produce a dead 
surface, and is much used for engraving on glass. An ink sold for writ- 
ing on glass with a steel pen is composed of barium and ammonium 
fluorides and sulphuric acid. 

Many ingenious experiments have been made in order to obtain fluorine 
in the separate state, but it was found that it invariably combined with 
some portion of the material of the vessel in which the operation was 
conducted. The most successful of the early attempts to isolate fluorine 
appears to have been made, at the suggestion of Davy, in a vessel of 
fiuor spar itself, which could not, of course, be supposed to be in any 
way affected by it. A greenish gas was obtained, possessing chemical 
properties similar to those of chlorine, but of much higher intensity. 
The difficulty, however, of obtaining vessels of fluor spar adapted to these 
experiments appears to have prevented any complete investigation of this 
most interesting element. 

The most recent experiments, in which the tetrafluorides of cerium 
and lead were decomposed by heat, have furnished a gas resembling 
chlorine in odour. 



184 FLUOKIDE OF SILICON. 

Solutions of the fluorides of potassium and the other alkaK metals cor- 
rode glass slowly, like hydrofluoric acid. These fluorides are capable of 
combining with the acid ; thus fluoride of potassium forms KF.HF, 
which, when dry, is a convenient source of hydrofluoric acid gas when 
moderately heated. The only fluoride possessed of much practical in- 
terest beside the fluoride of calcium, is the mineral kryolite (Kpvos, frost), 
which is a double fluoride of aluminium and sodium (Na 3 AlF 6 ), found 
abundantly in Greenland, and valuable as a source of aluminium and 
soda. The topaz contains fluorine, but in what form of combination is 
not certain ; its other constituents are alumina and silica. 

Magnesium fluoride (MgF 2 ) forms the mineral Sellaite which is found, 
crystallised, in Savoy. 

Fluorides are also found, though in very small quantity, in sea water, 
and they have been discovered in plants and animals. Human bone con- 
tains about 2 per cent, of calcium fluoride. 

It will be remembered that fluorine is the only element which is not 
known to form any compound with oxygen. 

133. Silicon tetrafluoride (SiF 4 =104 parts by weight = 2 volumes). — 
If a mixture of powdered fluor spar and glass be heated, in a test-tube 
or small flask, with concentrated sulphuric acid, a gas is evolved which 
has a very pungent odour, and produces thick white fumes in contact 
with the air : it might at first be mistaken for hydrofluoric acid, but if a 
glass rod or tube be moistened with water and exposed to the gas, the wet 
surface becomes coated with a white film, which proves, on examination, 
to be silica. This result originated the belief that the gas consisted of 
fluoric (now hydrofluoric) acid and silica ; but Davy corrected this view 
by showing that it really contained no oxygen, and consisted solely of 
silicon and fluorine. The gas is now called silicon tetrafluoride, and 
represents silica in which the oxygen has been displaced by fluorine : 
the change of places between these two elements in the above experiment 
is represented by the subjoined equation — 

2CaF 2 + Si0 2 + 2H 2 S0 4 = 2CaS0 4 + SiF 4 .+ 2H 2 0. 

Fluor £,.,. c i l, • ■ 1 Calcium Silicon 

spar. S]hca - Sulphuric acid. sulphate . tetrafluoride. 

The formation of the crust of silica upon the wetted surface of the 
glass is due to a decomposition which takes place between the tetra- 
fluoride and the water, in which the oxygen and fluorine again change 
places; SiF 4 + 2H 2 = Si0 2 + 4HF. Since this latter equation shows 
that hydrofluoric acid is again formed, it would be expected that the 
glass beneath the deposit of silica would be found corroded by the acid ; 
this, however, is not the case, and when the experiment is repeated upon 
a somewhat larger scale, so that the water which has acted upon the 
gas may be examined, it will be found to hold in solution, not hydrofluoric 
acid, but an acid which has little action upon glass, and is composed of 
hydrofluoric acid and fluoride of silicon, so that the hydrofluoric acid pro- 
duced when water acts upon the fluoride, combines with a portion of the 
latter to produce the new acid 2HF.SiF 4 , or H^SiF^, hydrofluo-silicic acid. 

For the preparation of silicon tetrafluoride, ] oz. of fluor spar, andl oz. of powdered 
glass are mixed together, and heated in a Florence flask, with 7 oz. (measured) of 
oil of vitriol, the gas being collected in dry bottles by downward displacement (see 
rig. 176, p. 157). If a little of the gas be poured from one of the bottles into a flask 
rilled up to the neck with water, the surface of the latter will become covered with 



HYDROFLUO-SILICIC ACID. 



185 



a layer of silica, so that if the flask be quickly inverted, the water will not pour from 
it, and will seem to have been frozen. In a similar manner, a small tube tilled with 
water and lowered into a bottle of the gas, will appear to have been frozen when 
withdrawn. A stalactite of silica some inches in length may be obtained by allow- 
ing water to drip gently from a pointed tube- into a bottle of the gas. Characters 
written on glass with a wet brush are rendered opaque by pouring some of the gas 
upon them. 

134 Hydrofluo-silicic acid or silico-fluoric acid (H 2 SiF 6 = 144 parts by- 
weight).— This acid is obtained in solution by passing silicon tetrafluoride 
into water — 

3SiF 4 + 2H 2 = 2H 2 SiF 6 + Si0 2 . 

The gas must not be passed directly into the water, lest the separated 
silica should stop the orifice of the tube, to prevent which the latter 
should dip into a little mercury 
at the bottom of the water, 
when each bubble, as it rises 
through the mercury into the 
water, will become surrounded 
with an envelope of gelatinous 
silica, and if the bubbles be 
very regular, they may even 
form tubes of silica extending 
through the whole height of 
the water. 

Crystals of H 2 SiF 6 ,2Aq. 
have been obtained by passing 
SiF 4 into solution of HF. 

For preparing hydrofluo-silicic 
acid, it will be found convenient to 
employ a gallon stoneware bottle 
(fig. 191), furnished with a wide 
tube dipping into a cup of mercury 
placed at the bottom of the water. 
1 lb. of finely powdered tiuor spar, 

1 lb. of fine sand, and 64 measured ounces of oil of vitriol are introduced into the 
bottle, which is gently heated upon a sand-bath, the gas being passed into about 5 
pints of water. After six or seven hours the water will have become pasty, from the 
separation of gelatinous silica. It is poured upon a filter, and when the liquid has 
drained through as far as possible, the filter is wrung in a cloth, to extract the 
remainder of the acid solution, which will have a sp. gr. of about 1"078. 

A dilute solution of hydrofluo-silicic acid may be concentrated by evapo- 
ration up to a certain point, when it begins to decompose, evolving fumes 
of silicon tetrafluoride, hydrofluoric acid remaining in solution and volatilis- 
ing in its turn if the heat be continued. Of course the solution corrodes 
glass and porcelain when evaporated in them. If the solution of hydrofluo- 
silicic acid be neutralised with potash, and stirred, a very characteristic 
crystalline precipitate of potassium silico-fluoride is formed — 

H 2 SiF 6 + 2KHO = K 2 SiF 6 {Potassium silico-fluoride) + 2H 2 . 

But if an excess of potash be employed, a precipitate of gelatinous silica 
will be separated, potassium fluoride remaining in the solution — 

+ 6KHO = 6KF + 4H 2 + Si0 2 . 

One of the chief uses of hydrofluo-silicic acid is to separate the potassium 




Fig. 191. — Preparation of hydrofluo-silicic 
acid. 



H 2 SiF 6 



186 GENERAL REVIEW OF THE HALOGENS. 

from its combination with certain acids, in order to obtain these in the 
separate state. 

135. Boron trifluoride (BF 3 ) may be prepared by a process similar to that employed 
for silicon fluoride, but it is also obtained by strongly heating a mixture of powdered 
boraeic anhydride with twice its weight of fluor spar in an iron tube ; 3CaF 9 + B.,Oo 
= 3CaO + 2BF 3 . 

The boron fluoride is a gas which fumes strongly in moist air, like the silicon 
fluoride. It is absorbed eagerly by water, with evolution of heat. One volume of 
water is capable of dissolving 700 volumes of boron fluoride, producing a corrosive 
heavy liquid (sp. gr. 177), which fumes in air, and chars organic substances on 
account of its attraction for water. This solution is known as fluoboric or boroftuoric 
acid, and its formation is explained by the equation — 

2BF 3 + 3H 2 = B. 2 3 .6H.F (Fluoboric acid). 

When the solution is heated, it evolves boron fluoride, until its specific gravity is 
reduced to 1 '58, when it distils unchanged. 

HydroHuoboric acid is obtained in solution by adding a large quantity of water to 
fluoboric acid ; 2(B 2 3 . 6HF) = H 3 B0 3 + 3H 2 + 3HBF 4 (Hydroftuoboric acid). 

This acid resembles the hydrofluo-silicic ; its hydrogen may be exchanged for 
metals to form borofluorides. 

136. General review of chlorine, bromine, iodine, and fluorine. — These 
four elements compose a natural group, the members of which are con- 
nected by the similarity of their chemical properties far more closely than 
those of any other group of elements. They are usually styled the 
halogens, from their tendency to produce salts resembling sea salt in their 
composition (aAs, the sea), and such salts are called haloid salts. These 
elements are also called salt-radicals, from their property of forming salts 
by direct union with the metals. Each of these elements is monatomic, 
and combines with an equal volume of hydrogen to form an acid which 
occupies the joint volumes of its constituents. 

The halogens also supply the most prominent example of the gradation 
in properties sometimes observed among the members of the same natural 
group of elements. 

In the order of their chemical energy, that is, of the force with which 
they hold other elements in chemical combination with them, fluorine 
sbould stand first, its combining energy being so great as to cause a serious 
difficulty in isolating it all; chlorine would rank next, then bromine, and 
iodine last. 

The atomic weights follow the inverse order of their chemical energies : 
fluorine, 19; chlorine, 35*5; bromine, 80; iodine, 127, — numbers which, 
of course, also represent their relative specific gravities in the state of 
vapour. 

A similar gradation is observed in the physical state and colour of those 
three which are well known, chlorine being a yellow gas, bromine a red 
liquid, boiling at 145° F., and iodine a black solid, boiling at 347° F. 

Even in the exceptions which occur to the order of chemical energy 
above alluded to, the same progression is noticed: thus fluorine has so 
little attraction for oxygen that no oxide is known ; chlorine has less 
attraction for oxygen than bromine (chloric acid being less stable than 
bromic), whilst bromine has less than iodine, which is said to be capable 
even of uniting directly with ozonised oxygen to form iodic acid. 

The compounds of these elements with hydrogen are all gases distin- 
guished by a powerful attraction for moisture and great similarity of 
odour. 



ORES AND MINERALS CONTAINING SULPHUR. 187 

Their potassium-salts all crystallise in the same (cubical) form. 

The silver fluoride is deliquescent and soluble in water ; the chloride 
is insoluble in water, but dissolves very easily in ammonia ; the bromide 
dissolves with some difficulty in ammonia ; and the iodide is insoluble. 

SULPHITE. 

S = 32 parts by weight = 1 volume (at 1900° F.). 

137. Sulphur is remarkable for its abundant occurrence in nature in 
the uncombined state, in many volcauic districts. It is also found, as 
sulphuretted hydrogen, in many mineral waters, and very abundantly in 
combination witb metals, forming the numerous ores known as sul/phurets 
or sulphides, of which the following are the most abundant: — 

Iron pyrites, Iron disulphide, FeS 2 

Copper pyrites, Sulphide of iron and copper, Cu 2 S.Fe 2 S 3 

Galena, Sulphide of lead, PbS 

Blende, Sulphide of zinc, ZnS 

Crude antimony, Sulphide of antimony, Sb 2 S 3 

Cinnabar, Sulphide of mercury, HgS . 

Sulphur is plentifully distributed also, in combination with oxygen 
and a metal, in the form of sulphates, of which the most conspicuous 
are : — 

Gypsum, Sulphate of calcium, CaS0 4 .2H 2 

Heavy spar, Sulphate of barium, BaS0 4 

Celestine, Sulphate of strontium, SrS0 4 

Epsom salts, Sulphate of magnesium, MgS0 4 .7H 2 

Glauber's salt, Sulphate of sodium, Na 2 SO 4 .10H 2 O. 

In plants, sulphur is also found in the form of sulphates, and as a con- 
stituent of the vegetable albumen (of which it forms about 1*5 per cent.) 
present in the sap. It is also contained in certain of the essential oils 
remarkable for their peculiar pungent odour, such as — 

Esssence of garlic, C 6 H 10 S . 
Essence of mustard, C 4 H 5 NS . 

In animals, sulphur occurs as sulphates, as a constituent of albumen, 
fibrine, and caseine (in neither of which does it exceed 2 per cent.) ; and 
in bile, one of the products from which (taurine, C 2 H 7 N0 3 S) contains 25 
per cent, of sulphur. 

For our supplies of sulphur we are chiefly indebted to Sicily, where 
large quantities of it are found in an uncombined state in beds of blue 
clay. Magnificent crystalline masses of strontium sulphate are often 
found associated with it ; the sulphur itself sometimes occurs in the 
form of transparent yellow octahedra, but more frequently in opaque 
amorphous masses. The districts in which sulphur are found are usually 
volcanic, and those which border the Mediterranean are particularly rich 
in it. Sulphur has also been found in Iceland and California. 

The native sulphur being commonly distributed in veins through masses 
of gypsum and celestine has to be separated from these by the action of 
heat. When the ores contain more than 12 per cent, of sulphur, the bulk 
of it is melted out, the ore being thrown into rough furnaces or cauldrons 
with a little fuel, and smothered up with earth, so as to prevent the com- 
bustion of the sulphur, which runs down in the liquid state to the bottom 



188 



EXTRACTION OF SULPHUR. 



of the cauldron, and is drawn out into wooden moulds.* But when the 
proportion of sulphur is small, the ore is heated so as to convert the 
sulphur into vapour, which is condensed in another vessel. The operation 
is conducted in rows of earthen jars (A, fig. 192), heated in a long furnace, 
and provided with short lateral pipes, which convey the sulphur into 
similar jars (B) standing outside the furnace, in which the vapour of sul- 
phur condenses in the liquid state, and flows out into pails of water. The 




Distillation of sulphur. 



sulphur obtained by this process is imported as rough sulphur, and con- 
tains 3 or 4 per cent, of earthy impurities. In order to separate these, it 
is redistilled, in this country, in an iron retort (A, fig. 193), from which 
the vapour is conducted into a large brick chamber (B), upon the sides of 
which it is deposited in the form of a pale yellow powder {flowers of sul- 
phur, or sublimed sulphur). "When the operation has been continued for 
some time, the walls of the chamber become sufficiently hot to melt the 




Fig. 193. — Sulphur refinery. 

sulphur, which is allowed to collect, and afterwards cast in wooden 
moulds, forming roll sulphur or brimstone. Distilled sulphur is obtained 
by allowing the vapour to pass from the retort into a small receiving- 
vessel (C) cooled by water, where it condenses in the liquid state : this 

* High pressure steam has been applied with advantage for melting the sulphur out of 
the ores, which are enclosed in an iron vessel, or the ores are heated in a boiler with a 66 
per cent, solution of calcium chloride at 120° C. The sulphur is sometimes extracted by- 
dissolving it with carbon disulphide. 



SULPHUR DISTILLED FROM PYRITES. 



189 



variety of sulphur is preferred for the manufacture of gunpowder, for 
reasons which will be stated hereafter. 



Sulphur is readily distilled on a small scale, in a 
flask cut off at the neck being employed as a 
receiver. The flask containing the sulphur should 
be supported upon a thin iron wire triangle, and 
heated by a gauze-burner, at first gently, and after- 
wards to the full heat. Flowers of sulphur will at 
first condense in the receiver, and will be followed 
by distilled sulphur when the temperature increases. 
A slight explosion of the mixture of sulphur vapour 
and air may take place at the commencement of the 
distillation. An ounce of sulphur may be distilled 
in a few minutes. 



Florence flask (fig 



another 




194.— Distillation of 
sulphur. 



We are by no means entirely dependent 
upon Sicily for sulphur, for this element can 
be easily extracted from iron and copper pyrites, both of which are found 
abundantly in this country. 

Iron pyrites forms the yellow metallic-looking substance which is 
often met with in masses of coal, sometimes in distinct cubical crystals, and 
which is to be picked up in large quantities on some sea-beaches, where it 
occurs in rounded nodules, 
rusty outside, but having 
a fine radiated metallic 
fracture. When this 
mineral is strongly heated, 
it gives up part of its 
sulphur ; at a very high 
temperature one-half of 
the sulphur may be sepa- 
rated, FeS 2 = FeS + S, but 
by an ordinary furnace 
heat only about one-fourth 
can be obtained. The 
distillation of iron pyrites 
is sometimes effected in 
conical fireclay vessels (fig. 
195) closed at the wider 
end, and stopped towards the other with a perforated plate, to allow the 
passage of the sulphur vapour. Each vessel contains 100 lbs. of pyrites, 
and yields 14 lbs. of sulphur. 

The sulphur obtained in this way has a green colour, due to the pre- 
sence of a little sulphide of iron carried over mechanically during the 
distillation : in order to purify it, it is melted and allowed to cool slowly, 
when the sulphide of iron subsides : the upper portion of the mass is then 
further purified by distillation. 

Sulphur may also be obtained from copper pyrites (Cu 2 S.Fe 2 S 3 ) in the 
process of roasting the ore, previously to "the extraction of the copper. 
The ore is heaped up into a pyramid, the base of which is about 30 feet 
square : a layer of powdered ore is placed at the bottom, to prevent too 
rapid access of air : above this there is a layer of brushwood : a wooden 
chimney is placed in the centre, and is made to communicate with air- 
passages left between the faggots : around this chimney the large fragments! 




195. 



-Furnace for distillation of sulphur 
from pyrites. 



190 ACTION OF HEAT UPON SULPHUR. 

of the ore are piled to a height of about 8 feet, and a layer of powdered 
ore, about 12 inches deep, is strewn over the whole. The heap contains 
about 2000 tons of pyrites, and will yield 20 tons of sulphur. The fire 
being kindled by dropping lighted faggots down the chimney, burns very 
slowly, because of the limited access of air, and after a few days sulphur 
is seen to exude from the surface, and is received in cavities made for 
the purpose in different parts of the heap. The roasting requires five or 
six months for its completion. In this operation a part of the sulphur 
has been separated by the mere action of heat, and another part has been 
displaced by the oxygen of the air, which has converted a portion of the 
iron into an oxide. A part of the separated sulphur has been burnt, the 
rest having escaped combustion on account of the limited access of air. 

The sulphur extracted from pyrites is generally found to contain a little 
arsenic, which is frequently associated with those minerals. Immense 
quantities of sulphur are consumed in this country for the manufacture of 
sulphuric acid, gunpowder, lucifer matches, vulcanised caoutchouc, and 
for making the sulphurous acid gas employed in bleaching processes. 

Much sulphur has recently been extracted from the tank-waste of the 
alkali works, by a process which will be described in the manufacture of 
carbonate of soda. 

138. Properties of sulphur. — In its ordinary forms sulphur has a 
characteristic yellow colour, though milk, of sulphur, or precipitated sul- 
phur (obtained by adding an acid to the solution of sulphur in an alkali), 
is white. It suffers electrical disturbance with remarkable facility, so 
that when powdered in a dry mortar it clings to it with great pertinacity. 
One of the most remarkable features of sulphur is its inflammability, 
due to its tendency to combine with oxygen at a moderately elevated 
temperature. It melts at a heat not much above the boiling-point of 
water (239° F.), and inflames at about 500° F., burning with a pale blue 
flame, and emitting the well-known suffocating odour of sulphurous acid 
gas (S0 2 ). The changes in the physical condition of this element under 
the influence of heat are very extraordinary. If 
a quantity of sulphur be introduced into a Florence 
flask and subjected to a gradually increasing heat 
(fig. 196), it is soon converted into a pale yellow 
limpid liquid (250° F.), the colour of which 
becomes gradually brown as the temperature rises, 
until, at about 350° F., it is nearly black and 
opaque, and is so viscid that the flask may be 
inverted without spilling it: at this point the 
temperature of the sulphur remains stationary for 
a time, notwithstanding that it is still over the 
flame, showing that heat is becoming latent in 
Fio- 196 converting the sulphur into the new modification. 

On continuing the heat the sulphur once more 
becomes liquid (500°), though not so mobile as at first, and at a much 
higher temperature (836° F.) it boils, and is converted into a brownish 
red, very heavy vapour : at this point of the experiment an explosion of 
the mixture of sulphur vapour with air often takes place. The flask 
may now be removed from the flame, and a little of the sulphur poured 
into a vessel of water, through which it will descend in a continuous 
stream, forming a soft elastic string like india-rubber : the portion remain- 




ELECTEO- POSITIVE AND ELECTRO-NEGATIVE SULPHUR. 191 

ing in the flask will be observed, as it cools, to pass again through the 
same states, becoming viscid at 350°, and very liquid at 250° ; another 
portion may now be poured into water, through which it will fall in 
isolated drops, solidifying into yellow brittle crystalline buttons of ordinary 
sulphur. As the portion of sulphur left in the flask cools, it will be 
found to deposit small tufts of crystals, and ultimately to solidify altogether 
to a yellow crystalline mass. 

The brown ductile sulphur, when kept for a few hours, will become yel- 
low and brittle, passing, in great measure, spontaneously into the crystalline 
sulphur. The change is accelerated by a gentle heat, and is attended with 
evolution of the heat which the sulphur was found to absorb at 350° Y. 
Both these varieties of sulphur are of course insoluble in water, and they 
are not dissolved to any great extent by alcohol and ether. If the crystal- 
line variety be shaken with a little carbon disulphide, it rapidly dissolves, 
and on allowing the solution to evaporate spontaneously, it deposits 
beautiful octahedral crystals, resembling those of native sulphur (rig. 197). 
Ductile sulphur, however, is insoluble in carbon disulphide. 

When flowers of sulphur are shaken with carbon disulphide, a con- 
siderable quantity passes into solution, the remainder consisting of the 
amorphous, or insoluble sulphur. Roll sulphur dissolves to a greater 
extent, and sometimes entirely, in the disulphide, and distilled sulphur 
is always easily soluble. 

The soluble and insoluble forms of sulphur appear to represent distinct 
chemical varieties of the element. When a solution of hydric sulphide 
(H 2 S) is decomposed by the galvanic battery, the hydrogen, as would be 
expected, is separated at the negative pole, and the sulphur at the positive 
pole (p. 8). The sulphur, therefore, was the electro-negative element of 
the compound. This sulphur is soluble in carbon disulphide. When 
an acid is added to a solution of an alkaline sulphide containing 
more than one atom of sulphur, the excess of the latter is precipi- 
tated, and is then also found to be soluble in carbon disulphide ; for it 
played an electro-negative part towards the metal with which it was in 
combination. 

When sulphurous acid is decomposed by the battery, the sulphur is 
separated at the negative pole, showing that it played an electropositive 
part in the sulphurous acid. This electro-positive sulphur is insoluble in 
carbon disulphide. The sulphur in the chloride of sulphur (S 2 C1 2 ) also 
plays an electro-positive part, and accordingly when this compound is 
decomposed by water, the sulphur which separates is insoluble in carbon 
disulphide. The existence of these two forms of sulphur affords some 
support to the theory of the dual constitution of the elements noticed at 
p. 53. When a beam of solar light is thrown by a lens through a solu- 
tion of sulphur in carbon disulphide, a precipitation of insoluble sulphur 
takes place in the track of the beam. 

The electro-positive sulphur would be expected to manifest a greater 
attraction for oxygen than the electro-negative variety, and accordingly it 
is found to be far more easily oxidised by nitric acid. Electro-positive or 
insoluble sulphur is converted into electro-negative or soluble sulphur by 
the action of a moderate heat, itself evolving heat during the process of 
conversion : when melted in contact with sulphurous acid gas, the 
soluble sulphur is converted externally into the insoluble form. 

Crystalline or soluble sulphur is capable of existing in two distinct 



192 



ALLOTROPIC FORMS OF SULPHUR. 




Fig. 197. 



Fig. 198. 



forms. The natural form of crystallised sulphur is the octahedron with 
a rhombic base (fig. 197), and this is the usual form which sulphur 

assumes when crystallised from its solutions. 
But if sulphur be melted in a covered 
crucible, allowed to cool until the surface 
has congealed, and the remaining liquid 
portion poured out after piercing the crust 
(with two holes, one for admission of air), 
the crucible will be lined with beautiful 
needles, which are oblique prisms (fig. 198). 
These crystals are brownish - yellow and 
transparent, when freshly made, but they 
soon become opaque yellow; and although 
they retain their prismatic appearance, they have now changed into minute 
rhombic octahedra, the change being attended with evolution of heat.* 
On the other hand, if a crystal of octahedral sulphur be exposed for a 
short time to a temperature of about 230° F. (in a boiling saturated 
solution of common salt, for example), it becomes opaque, in consequence 
of the formation of a number of minute prismatic crystals in the mass. 

The difference between these two forms of crystalline sulphur extends 
to their fusing-points and specific gravities, the prismatic sulphur fusing at 
248° F., and the octahedral sulphur at 239° F., the specific gravity of 
the prisms being 1*98, and that the octahedra 2*05. 

Eoll sulphur when freshly made, consists of a mass of oblique prismatic 
crystals, but after being kept for some time, it consists of octahedra, although 
the mass generally retains the specific gravity proper to the prismatic form. 
This change in the structure of the mass, taking place when its solid 
condition prevented the free movement of the particles, gives rise to a 
state of tension which may account for the extreme brittleness of roll sul- 
phur. If a stick of sulphur be held in the warm hand, it often splits, 
from unequal expansion. These peculiarities of sulphur deserve careful 
study, as helping to elucidate the spontaneous alterations in the structure 
of glass, iron, &c, under certain conditions. 

Flowers of sulphur do not present a crystalline structure, but consist of 
spherical granules composed of insoluble sulphur enclosing soluble sulphur. 
Hot oil of turpentine dissolves sulphur freely, and when the solution is 
allowed to stand, the crystals which are deposited whilst the solution is 
hot have the prismatic form, but as it cools, octahedra are separated. 
The following table exhibits the chief allotropic forms of sulphur : — 



Octahedral . . 
Electro-negative . 
Prismatic . 


: ! 


Sp. gr. 
2-05 
1-98 


Fusing point. In Carbon Disulphide 
239° F. Soluble. 
248° Soluble. 


Ductile 

Amorphous . . 
Electro-positive . 


': j 


1-96 


Becomes octahedral. Insoluble. 



The octahedral is by far the most stable of the three, and is the ultimate 
condition which the others assume. 

Other varieties of sulphur, such as a black and a red modification, have 
been described, but they are of minor importance. 

* Spring lias shown that a pressure of 6000 atmospheres converts prismatic sulphur and 
plastic sulphur into the octahedral variety. 




SPECIFIC GRAVITY OF SULPHUR VAPOUR. 193 

Sulphur is capable of entering into direct combination with several other 
elements. It unites with chlorine and with some of the metals, if finely 
divided, even at the ordinary temperature, and it is capable of combining 
at a high temperature with all the non-metals except nitrogen, and with 
nearly all the metals. 

If a mixture of 2 parts of copper filings and 1 part of sulphur, or of equal weights 
of iron filings and sulphur, be heated in a Florence flask or a test-tube, the combina- 
tion will be attended with vivid combustion. 

The so-called Lemerifs volcano was made by mixing iron 
filings with two-thirds of their weight of powdered sulphur, 
and burying several pounds of the moist mixture in the 
earth, when the heat evolved by the rusting of part of the 
iron provoked the energetic combination of the remainder 
with the sulphur, and the consequent development of much 
steam.* Firework compositions containing iron filings 
and sulphur may cause ignition if damp. 

Several metals may be made to burn in sulphur vapour, 
as in oxygen, by heating the sulphur in a Florence flask, 
with a gauze burner, so as to keep the flask constantly filled 
with the brown vapour. Potassium and sodium, introduced 
in deflagrating spoons, take fire spontaneously in the 
vapour (fig. 199). 

A coil of copper wire glows vividly in sulphur vapour, "'" 

and becomes converted into a brittle mass of sulphide of Fig- 199. 

copper. When sulphur is exposed to sunshine in an at- 
mosphere of hydride of antimony or arsenic, it becomes converted into hydrosulphurie 
acid gas and sulphide of antimony or arsenic. 

Sulphur dissolves, though slowly, in boiling concentrated nitric and 
sulphuric acids, being oxidised by the former into sulphuric acid, and by 
the latter into sulphur dioxide. It is far more rapidly converted into 
sulphuric acid by a mixture of nitric acid and potassium chlorate. The 
alkalies dissolve sulphur when heated, yielding yellow or red solutions 
which contain hyposulphites and sulphides of the alkali metals. 

There is a very general resemblance in composition between the com- 
pounds of sulphur and those of oxygen with the same elements. 

139. Influence of temperature upon the specific gravity of gases and 
vapours.' — The specific gravity of a gas or vapour being defined as its 
weight compared with that of an equal volume of dry and pure air at the 
same temperature and pressure, it might be supposed that so long as the 
temperatures were equal, their actual thermo metric value would not in- 
fluence the specific gravity. Indeed, with those gases and vapours which 
are condensible with difficulty, this is actually the case. Thus, if equal 
volumes of oxygen and air be weighed, either at a low or a high tempera- 
ture, provided their temperatures are the same, their weights will always 
stand to each other nearly in the ratio of 1T057 : 1. 

But with many vapours it is found that if they be weighed at tempera- 
tures too nearly approaching to their condensing points, their specific 
gravities are much higher than they are found to be at higher tempera- 
tures. Sulphur affords a very well-marked instance of this. It boils at 
836° F., and if its vapour be weighed at a temperature of 900°F., it is 
found to weigh 6*617 times as much as an equal volume of air at 900° F., 
so that it is 96 times as heavy as hydrogen, or 1 atom of sulphur would 

^Rust-joint cement is a mixture of 80 parts iron filings, 1 of sal ammoniac, and 2 of sul- 
phur, made into a paste with water ; it is very useful for making the joints of iron tubes 
air-tight, for it sets into a hard cement, the iron combining with the sulphur. 



194 



SOURCES OF SULPHURETTED HYDROGEN. 



occupy J volume. But if the vapour of sulphur be weighed at 1900° F., it 
is found to weigh only 2 "23 times as much as an equal volume of air at 
the same temperature and pressure, so that it is only 32 times as heavy 
as hydrogen, and 1 atom of sulphur occupies 1 volume. 

According to Troost, the sulphur vapour at 900° F. is really a con- 
densed molecule, like ozone, since its specific gravity remains unaltered 
under diminished pressure. 



Hydrosulphuric Acid. 

H 2 S = 34 parts by weight = 2 volumes. 

140. Sulphuretted hydrogen or hydric sulphide, or hydrosulphuric acid, 
has been already mentioned as occurring in some mineral waters, as at 
Harrowgate. It is also found in the gases emanating from volcanoes, 
sometimes amounting to one-fourth of their volume. It is a product of 
the putrefaction of organic substances containing sulphur, and is one of 
the causes of the sickening smell of drains, &c. Eggs, which contain a 
considerable proportion of sulphur, evolve sulphuretted hydrogen as soon 
as they begin to change, and hence the association between this gas and 
the " smell of rotten eggs." The same smell is observed when a kettle 
boils over upon a coke or coal fire, the hydrogen liberated from the water 
combining with the sulphur present in the fuel. 

Hydrosulphuric acid is also found among the products of destructive 
distillation of organic substances containing sulphur ; it was mentioned 
among the products from coal, in which it is for the most part combined 
with the ammonia formed at the same time, producing ammonium 
sulphide. 

It may be produced, though not in large quantity, by the direct union 
of hydrogen with sulphur vapour at a high temperature, or by passing a 
mixture of sulphur vapour and steam through a tube filled with red hot 
pumice stone (the latter encouraging the action by its porosity). Hydro- 
sulphuric acid is more readily formed by heating a damp mixture of 

sulphur and wood charcoal, 
and may be obtained in large 
quantity by heating a mix- 
ture of equal weights of 
sulphur and tallow, the latter 
furnishing the hydrogen. 

Preparation of hydrosul- 
phuric acid. — For use in the 
laboratory, where it is very 
largely employed in testing 
for and separating metals, 
hydrosulphuric acid is gener- 
ally prepared by decomposing 
ferrous sulphide with diluted 
sulphuric acid ; FeS + H 2 S£) 4 
= H 2 S + FeS0 4 {ferrous sid- 
phate). 

To obtain ferrous sulphide, a mixture of 3 parts of iron filings with 2 parts of 
flowers of sulphur is thrown, by small portions at a time, into an earthen crucible 
(A, fig. 200) heated to redness in a charcoal fire, the crucible being covered after 




PREPARATION OF SULPHURETTED HYDROGEN. 



195 




Fig. 201.— Preparation of 
hydrosulphuric acid. 



each portion has been added. The iron and sulphur combine, with combustion, and 

when the whole of the mixture has been introduced, the crucible is allowed to cool, 

the mass of ferrous sulphide broken out, and a few fragments of it are introduced 

into a bottle (fig. 201) provided with a funnel tube for the addition of the acid, and 

a bent tube for conducting the gas through a small 

quantity of water, to remove any splashes of ferrous 

sulphate. From the second bottle the gas is conducted 

by a glass tube with a caoutchouc joint, either down 

into a gas-bottle, or into water, or any other liquid 

upon which the gas is intended to act. The fragments 

of ferrous sulphide should be covered with enough 

water to fill the gas-bottle to about one-third, and 

strong sulphuric acid added by degrees through the 

funnel, the bottle being shaken until effervescence is 

observed. An excess of strong sulphuric acid stops 

the evolution of gas by precipitating a quantity of 

white anhydrous ferrous sulphate, which coats the 

sulphide and defends it from the action of the acid. 

"When no more gas is required, the acid liquid should be at once poured away, leaving 

the fragments of ferrous sulphide at the bottom of the bottle for a fresh operation. 

The liquid, if set aside, will deposit beautiful green crystals of copperas or ferrous 

sulphate (FeS0 4 , 7H 2 0). 

Since the ferrous sulphide prepared as above generally contains a little metallic 
iron, the sulphuretted hydrogen is mixed with free hydrogen, which does not gene- 
rally interfere with its uses. The pure gas may be prepared by heating antimony sul- 
phide (crude antimony) in a flask with hydrochloric acid — 

Sb 2 S 3 + 6HC1 = 3H. 2 S + 2SbCl 3 . 

If hydrochloric acid be diluted with more than 6 molecules of water, it is not 
capable of decomposing the antimony sulphide ; hence, when the sulphide is heated 
with an acid somewhat stronger than this, the subsequent addition of water repre- 
cipitates the antimony sulphide with the orange colour which it always presents 
when precipitated. 

Properties of hydrosulpliuric acid. — This " gas is at once distinguished 
f ,'om all others by its disgusting odour. It is one-fifth heavier than air 
(sp. gr. 1 "1912). Its gaseous state is not permanent, but a pressure of 
17 atmospheres is required to reduce it to a colourless liquid, which 
congeals to a transparent solid at - 122° F. Water absorbs about three 
times its volume of sulphuretted hydrogen at the ordinary temperature ; 
both the gas and its solution are feebly acid to blue litmus paper. The 
gas is very combustible, burning with a blue flame like that of sulphur, 
and yielding, as the chief products, water and sulphurous acid gas H 2 S 
+ 3 = H 2 + S0 2 ; a little sulphuric acid (H 2 SG 4 ) is also formed, and 
unless the supply of air is very good, some of the sulphur will be separated; 
thus, if a taper be applied to a bottle filled with sulphuretted hydrogen, 
a good deal of sulphur will be deposited upon the sides. This combusti- 
bility of sulphuretted hydrogen is of the greatest importance in those 
processes of chemical manufacture in which this gas is evolved (as in the 
preparation of ammoniacal salts from gas liquors), enabling it to be dis- 
posed of in the furnace instead of becoming a nuisance to the neighbour- 
hood. The gas causes fainting when inhaled in large quantity/ and 
appears much to depress the vital energy when breathed for any length 
of time even in a diluted state. 

When dissolved in water, hydrosulphuric acid is slowly acted upon by 
the oxygen of the air, which converts its hydrogen into water, and causes 
a white deposit of (electro-negative or soluble) sulphur. 

This is a great drawback to the use of this indispensable chemical in the labor- 
atory, since the solution of hydrosulphuric acid is so soon rendered useless. To 



196 PROPERTIES OF HYDROSULPHURIC ACID. 

obviate it as far as possible, the solution should be made either with boiled water (free 
from dissolved air), or with water which has already been once charged with the gas 
and spoilt by keeping, for all the oxygen dissolved in this water will have been con- 
sumed by the former portion of gas. The gas should be passed through the water 
until, on closing the bottle with the hand and shaking violently, the pressure is 
found to act outwards, showing the water to be saturated with the gas. By closing 
the bottle with a greased stopper, and inverting it, the solution may be preserved 
for some weeks, even though occasionally opened for use. 

In preparing the solution of hydrosulphuric acid, a certain quantity of the gas 
always escapes absorption. To prevent this from becoming a nuisance, the bottle 
containing the water to be charged with gas may be covered with an air-tight 
caoutchouc cap having two tubes, through one of. which passes the glass tube con- 
veying the gas down into the water, and through the other, a tube conducting the 
excess of gas either into a gas-burner, where it may be consumed, or into a solution of 
ammonia which will absorb it, forming the very useful ammonium sulphide. 

Concentrated nitric acid acts upon hydric sulphide, oxidising the 
hydrogen and a part of the sulphur, ammonium sulphate being found in 
the solution, and a pasty mass of sulphur separated. Chlorine, bromine, 
and iodine at once appropriate its hydrogen and separate the sulphur. 

The hydrogen of the hydrosulphuric acid is oxidised immediately by 
nitrous anhydride (N 2 3 ), the sulphur being separated, and a considerable 
quantity of ammonia produced ; -N 2 3 + 6H 2 S = 2NH 3 + 3H 2 + S 6 . 

In its action upon the metals and their oxides, hydrosulphuric acid 
resembles hydrochloric and the other hydrogen acids. Many of the metals 
displace the hydrogen and form metallic sulphides. This usually requires 
the assistance of heat, but mercury and silver act upon the gas at the 
ordinary temperature. Thus, if hydric sulphide be collected over mercury, 
the surface of the latter becomes coated with a black fdm of mercurous 
sulphide ; H 2 S + Hg 2 = H 2 + Hg 2 S. In a similar way the surface of 
silver is slowly tarnished when exposed to air containing sulphuretted 
hydrogen, its surface being covered with a black film of silver sulphide. 
It is on this account that silver plate is so easily blackened by the 
air of towns. An egg spoon is always blackened by the sulphur from the 
egg. Silver coins kept in the pocket with lucifer matches are blackened, 
from the formation of a little silver sulphide. The original brightness 
of the coin may be restored by rubbing it with a solution of potassium 
cyanide, which dissolves the silver sulphide. Friction with strong 
ammonia will also remove the tarnish, and its application is safer than 
that of the poisonous cyanide. 

When heated in the gas, several metals displace the hydrogen from it. 
Thus, potassium acts upon it in a corresponding manner to that in wdiich 
it acts upon water, forming potassium hydrosulplride (KHS). 

Tin removes the whole of the sulphur from hydrosulphuric acid at a 
moderate heat ; Sn + H 2 S = H 2 + SnS . 

When hydrosulphuric acid acts upon a metallic oxide, it generally con- 
verts it into a sulphide corresponding to the oxide, whilst the hydrogen 
and oxygen unite to form water. Lead oxide in contact with the gas 
yields black lead sulphide and water ; PbO + H 2 S = PbS + H 2 0. Paper 
impregnated with a salt of lead is used as a test for the presence of this 
gas. Thus, if paper be spotted with a solution of lead nitrate (or acetate) 
it will indicate the presence of even minute quantities of hydric sulphide 
(in impure coal gas, for example) by the brown colour imparted to the 
spots — 

Pb(N0 3 ) 2 + H 2 S = 2HN0 3 + PbS. 



SULPHIDES OF THE METALS. 197 

It is in this manner that paints containing white lead (lead carbonate) 
are darkened by exposure to the air of towns. Cards glazed with white 
lead, and engravings on paper whitened with that substance, suffer a 
similar change. Paintings, whether in oil or water-colours, in which 
lead is an ingredient, are also injured by air containing sulphuretted 
hydrogen. It has been found that such colours, damaged by the forma- 
tion of lead sulphide are restored by the continued action of light and air, 
the black sulphide becoming oxidised and converted into the white 
sulphate, PbS + 4 = PbS0 4 . In the dark this restoration does not take 
place, so that it is often a mistake to screen pictures from the light by a 
curtain. 

The action of hydrosulphuric acid upon the chlorides and other haloid 
salts of the metals generally resembles its action upon the oxides of the 
same metals. 

Most of the sulphides of the metals, like the corresponding oxides, are 
insoluble in water, but many of the sulphides are also insoluble in diluted 
acids and in alkalies, so that when hydrosulphuric acid is brought into 
contact with the solutions of metals, it will often precipitate the metal in 
the form of a sulphide having some characteristic colour or other property 
by which the metal may be identified. 

Any solution of lead will give a black precipitate with solution of hydrosulphuric 
acid, the lead sulphide being insoluble in diluted acids and in alkalies. 

A solution of antimony (tartar-emetic, for example, the tartrate of antimony and 
potassium) mixed with an excess of hydrochloric acid, gives an ora^c-coloured pre- 
cipitate (Sb. 2 S 3 ) on adding hydrosulphuric acid ; but if another portion be mixed with 
an excess of potash before adding the hydrosulphuric acid, there will be no precipi- 
tate, for the antimony sulphide is soluble in alkalies. 

Cadmium chloride gives a brilliant yellov: precipitate of cadmium sulphide on 
adding hydrosulphuric acid. 

Zinc sulphate yields a white precipitate of zinc sulphide (ZnS), but if a little hydro- 
chloric acid be previously added, no precipitate is formed, the zinc sulphide being 
soluble in acids. On neutralising the hydrochloric acid with ammonia, the zinc 
sulphide is at once precipitated. 

It is evident that, in a solution containing cadmium and zinc, the metals may be 
separated by acidifying the liquid with hydrochloric acid, and adding excess of 
hydrosulphuric acid, which precipitates the cadmium sulphide only. On filtering 
the solution, and adding ammonia, the zinc sulphide is precipitated. 

Sulphur -acids and sulphur-bases. — Those sulphides which are soluble 
in the alkalies are often designated sulphur-acids, whilst the sulphides of 
the alkali metals are sulphur-bases. These two classes of sulphides com- 
bine to form sulphur-salts analogous in composition to the oxygen-salts of 
the same metals. Thus, there have been crystallised, the salts — 

Sodium sulphostannate, . . . ]N"a 4 SnS 4 . 

,, sulphantimoniate, . . . !S T aSbS 3 . 

,, sulpharseniate, . . . Na 3 AsS 4 . 

The action of air upon the sulphides of the metals is often turned to 
account in chemical manufactures. At the ordinary temperature, the 
sulphides of those metals which form alkaline oxides (such as sodium 
and calcium), when exposed to the air in the presence of water, yield 
first, mixtures of the hydrate and bisulphide, 2ISTa 2 S + + H 2 — Na 2 S 2 
+ 2NaHO ; and afterwards the hyposulphite, Na 2 S 2 + 3 = JN"a 2 S 2 3 . This 
change is sometimes turned to account for the manufacture of sodium 
hyposulphite. 



198 PERSULPHIDE OF HYDROGEN. 

When the metal forms a less powerful base with oxygen, the sulphide 
is often converted into sulphate by exposure to moist air ; thus, CuS 
+ 4 = CuS0 4 , which is taken advantage of for the separation of copper 
from tin ores. 

The black ferrous sulphide (FeS), when exposed -to moist air, becomes 
converted into red ferric oxide, with separation of sulphur, 2FeS + 3 
= Fe 2 3 + S 2 , a change which enables the gas manufacturer to revive, by 
the action of air, the ferric oxide employed for removing the sulphuretted 
hydrogen from coal gas. 

When roasted in air at a high temperature, the sulphides correspond- 
ing to the more powerful bases are converted into sulphates ; thus, 
ZnS + 4 = ZnS0 4 , which explains the production of zinc sulphate by 
roasting blende. But in most cases part of the sulphur is converted into 
sulphurous acid gas at the same time. Cuprous sulphide, for instance, is 
partly converted into cupric oxide by roasting, Cu 2 S + 4 = 2CuO + S0 2 , 
a change of great importance in the extraction of copper from its ores. 

141. Hydric persulphide. — The composition of this substance is not yet satisfactorily 
ascertained. The similarity of its chemical properties to those of hydric peroxide 
prompts the wish that its formula may be H 2 S 2 . Some analyses, however, seem to 
lead to the formula H 2 S 5 , but since the persulphide is a liquid capable of dissolving 
free sulphur, which is not easily separated from it, there is much difficulty in deter- 
mining the exact proportion of this element with which the hydrogen is combined. 

"When equal weights of slaked lime and sulphur are boiled with water, an orange- 
coloured liquid is formed, which contains calcium hyposulphite, calcium disulphide, 
and calcium pentasulphide (CaS 5 ) ; 3CaO + S 6 = CaS 2 3 + 2CaS 2 . 

When hydrochloric acid is added, to the filtered solution, an abundant precipitation 
of sulphur occurs, and much hydrosulphuric acid is evolved — 

CaS 2 + 2HC1 = CaCl 2 + H 2 S + S. 

But if the solution be poured by degrees into a slightly warm mixture of hydro- 
chloric acid with twice its bulk of water, and constantly stirred, a yellow heavy oily 
liquid collects at the bottom, which is the hydric persulphide — 

CaS 2 + 2HC1 = H 2 S 2 (?) + CaCl 2 . 

The acid having been kept in excess, the persulphide has been preserved from the 
decomposition which it suffered in the presence of the alkaline solution in the. 
former experiment. For the hydric persulphide very closely resembles the peroxide 
in the facility with which it may be decomposed into hydrosulphuric acid and sulphur ; 
it undergoes spontaneous decomposition even in sealed tubes, and the hydrosulphuric 
acid then becomes liquefied by its own pressure. Most of the substances, the contact 
of which promotes the decomposition of the hydric peroxide, have the same effect 
upon the persulphide. This compound has a peculiar odour, which affects the eyes ; 
of course, its vapour is mixed with that of hydrosulphuric acid resulting from its 
decomposition. 

Oxides of Sulphur. 

142. Only two compounds of sulphur with oxygen have been obtained 
in the separate state, viz., sulphurous anhydride (S0 2 ) aud sulphuric 
anhydride (S0 3 ). 

Sulphur Dioxide or Sulphurous Anhydride. 
S0 2 = 64 parts by weight = 2 volumes. 

143. In nature, sulphurous acid gas is but rarely met with; it exists 
in the gases issuing from volcanoes. Although constantly discharged 
into the air of towns by the combustion of coal (containing sulphur), it is 
so easily oxidised and converted into sulphuric acid that no considerable 



PREPARATION OF SULPHUR DIOXIDE. 199 

quantity is ever found in the atmosphere. Sulphurous acid gas has been 
already mentioned as the sole product of the combustion of sulphur in dry 
air and oxygen,* but it is generally prepared for chemical purposes by 
removing part of the oxygen from sulphuric acid, which is easily effected 
by heating it with metallic copper — 

2H,S0 4 + Cu = CuS0 4 + 2H 2 + S0 2 . 

Sulphuric acid. Copper sulphate. 

300 grains of copper clippings are heated in a Florence flask with 4 oz. (measured) 
of strong sulphuric acid, the gas being conducted by a bent tube down to the bottom 
of a dry bottle closed with a perforated card (see tig. 176, p. 157). Some time will 
elapse before the gas is evolved, for sulphuric acid acts upon copper only at a high 
temperature ; but when the evolution of gas fairly commences, it will proceed very 
rapidly, so that it is necessary to remove the flame from under the flask. The gas 
will contain a little suspended vapour of sulphuric acid, which renders it turbid. 

When the operation is finished, and the flask has been allowed to cool, it will be 
found to contain a grey crystalline powder at the bottom of a brown liquid. The 
latter is the excess of sulphuric acid employed, and retains very little copper, since 
cupric sulphate is insoluble in strong sulphuric acid. If the liquid be poured off, 
and the flask filled up with water, and set aside for some time, the crystalline powder 
will dissolve, forming a blue solution of sulphate of copper, yielding that salt in fine 
prismatic crystals by evaporation and cooling. The dark powder remaining undis- 
solved after extracting the whole of the sulphate, consists chiefly of cuprous suphide, 
the production of which is interesting, as showing how far the deoxidising effect of 
the copper may be carried in this experiment. 

Sulphur dioxide is a very heavy (sp. gr. 2*25) colourless gas, character- 
ised by its odour of burning brimstone. It condenses to a clear liquid at 
0° F. (the temperature of a mixture of ice and salt) even at the ordinary 
pressure of the air, and has been frozen to a colourless crystalline solid 
at - 105° ¥. 

The liquefaction of the gas is easily exhibited by "passing it down to the bottom of 
a tube (A, fig. 202) closed at one end, and surrounded with a mixture of pounded 
ice with half its weight of salt. The tube should have 
been previously drawn out to a narrow neck at B, 
which may afterwards be sealed by the blowpipe, the 
lower part of the tube being still surrounded by the 
freezing mixture, since the liquid sulphur dioxide 
boils at 14° F. The tube need not be very strong, for 
at the ordinary temperature the vapour exerts a pressure 
of only 2*5 atmospheres. Liquid sulphur dioxide is a 
convenient agent for producing (by its rapid evapora- 
tion) thelow temperature ( - 39° F.) required to effect 
the solidification of mercury. A small globule of this 
metal may readily be frozen by dropping some liquid 
sulphur dioxide upon it in a watch-glass placed in a 
strong draught of air. The tube containing the sulphur 
dioxide should be held in a woollen cloth or glove. 
The attractive experiment of freezing water in a red 
hot crucible may also be made with the liquid. A Fig. 202. 

platinum crucible being heated to redness, and some 

liquid sulphur dioxide poured into it, from a tube which has been cooled for half an 
hour in ice and salt, the liquid becomes surrounded with an atmosphere of sulphurous 
acid gas, which prevents its contact with the metal (assumes the spheroidal state), 
and its temperature is reduced by its own evaporation to so low a degree that a little 
water allowed to flow into it will at once become converted into opaque ice. Liquid 
S0 2 is employed in freezing machines. The lowest temperature yet reached - 220° F. 
(-140° C.) is obtained by the evaporation of a solution of solid C0 2 in liquid S0 2 . 
This mixture was employed in liquefying oxygen, hydrogen, and nitrogen under very 
high pressure. 

* According to Berthelot, a notable quantity of S0 3 is produced at the same time. 




200 



BLEACHING BY SULPHUROUS ACID. 



Sulphurous acid gas is very easily absorded by water, as may be shown 
by pouring a little water into a bottle of the gas, closing the bottle with 
the palm of the hand, and shaking it violently (see fig. 164, p. 149), 
when the diminished pressure due to the absorption of the gas will cause 
the bottle to be sustained against the hand by the pressure of the 
atmosphere. Water absorbs 43*5 times its bulk of the gas at the ordi- 
nary temperature. The solution is believed to contain sulphurous acid, 
H 2 S0 3 , formed by the reaction H 2 + S0 2 = H Q S0 3 , but this body has 
not been obtained in the separate state. If the solution be exposed to a 
low temperature, a crystallised hydrate is obtained, the composition of 
which does not appear to be accurately settled. When the solution of 
sulphurous acid is kept for some time in a bottle containing air, its smell 
gradually disappears, the acid absorbing oxygen and becoming converted 
into sulphuric acid. 

Sulphur dioxide, like carbon dioxide, possesses in a high degree the 
power of extinguishing flame. A taper is at once extinguished in a 
bottle of the gas, even when containing a considerable proportion of air. 
One of the best methods of extinguishing burning soot in a chimney con- 
sists in passing up sulphurous acid gas by burning a few ounces of sulphur 
in a pan placed over the fire. 

The principal uses of sulphurous acid gas depend upon its property of 
bleaching many animal and vegetable colouring matters. Although a far 
less powerful bleaching agent than chlorine, it is preferred for bleaching 
silk, straw, wool, sponge, isinglass, baskets, &c, which would be injured 
by the great chemical energy of chlorine. The articles to be bleached 
are moistened with water and supended in a chamber in which sulphurous 
acid gas is produced by the combustion of sulphur. The colouring 
matters do not appear in general to be decomposed by the acid, but 
rather to form colourless combinations with it, for in course of time the 
original colour often reappears, as is seen in straw, flannel, &c, which 
become yellow from age, the sulphurous acid probably being oxidised into 
sulphuric acid. Stains of fruit and port wine on linen are conveniently 
removed by solution of sulphurous acid. 

The red solution obtained by boiling a few chips of logwood with river water 
(distilled water does not give so fine a colour), serves to illustrate the bleaching pro- 
perties of sulphurous acid. A few drops of the solution of 
the acid will at once change the red colour of the solution 
to a light yellow ; but that the colouring power is suspended 
and not destroyed, may be shown by dividing the yellow 
liquid into two parts, and adding to them, respectively, 
potash and diluted sulphuric acid, which will restore the 
colour in a modified form. To contrast this with the com- 
plete decomposition of the colouring matter, a little sul- 
phurous acid may be added to a weak solution of the 
potassium permanganate, when the splendid red solution 
at once becomes perfectly colourless, and neither acid nor 
alkali can effect its restoration. 

If a bunch of damp coloured flowers be suspended in a 
bell-jar over a crucible containing a little burning sulphur 
(fig. 203), many of the flowers will be completely bleached 
by the sulphurous acid, and by plunging them afterwards 
into diluted sulphuric acid and ammonia, their colours may be partly restored with 
some very curious modifications. 

Another very useful property of sulphurous acid is that of arresting 
fermentation (or putrefaction), apparently by killing the vegetable or 




Fig. 203. 




SULPHITES. 201 

animal growth which is the cause of the fermentation. This is commonly 
designated the antiseptic or antizymotic property of sulphurous acid, and 
is turned to account when casks for wine or beer are sulphured in order to 
prevent the action of any substance con- 
tained in the pores of the wood, and 
capable of exciting fermentation, upon the 
fresh liquor to be introduced. If a little 
solution of sugar be fermented with yeast 
in a flask provided with a funnel tube 
(fig. 204), a solution of sulphurous acid 
poured in through the latter will at once 
arrest the fermentation. The salts of sul- 
phurous acid (sulphites) are also occa- 
sionally used to arrest fermentation, in 
the manufacture of sugar, for instance. Fig. 204. 

Clothes are sometimes fumigated with 

sulphurous acid gas to destroy vermin, and the air of rooms is disinfected 
by burning sulphur in it. 

The disposition of sulphurous acid to absorb oxygen and pass into sul- 
phuric acid, renders it a powerful deoxidising or reducing agent. Solu- 
tions of silver and gold are reduced to the metallic state by sulphurous acid 
and sulphites. 

If a solution of sulphurous acid be heated for some time in a sealed tube to 340° F. 
one portion of the acid deoxidises another, sulphur is separated, and sulphuric acid 
formed; 3H 2 S0 3 = 2H 2 S0 4 + H 2 + S . 

Sulphurous acid gas combines with ammonia gas to form two solid compounds 
(NH 3 ) 2 S0 2 , andNH 3 .S0 2 . 

Chlorine combines with an equal volume of sulphur dioxide, under the influence 
of bright sunshine, or in presence of charcoal, to produce a colourless liquid, the 
vapour of which is very acrid and irritating to the eyes. Its composition is repre- 
sented by S0 2 C1 2 , and it is sometimes called chlorosulphuric acid, though it does not 
combine with bases, and is decomposed by water, yielding hydrochloric and 
sulphuric acids. It is also known as chloride of sulphuryle. The chloride of thionyle,* 
SOCl 2 , is a colourless volatile liquid obtained by the action of sulphurous acid gas on 
phosphorus pentachloride. It is decomposed by water, yielding hydrochloric and 
sulphurous acids. 

Potassium and sodium, when heated in sulphurous acid gas, burn vividly, pro- 
ducing the oxides and sulphides of the metals. 

Iron, lead, tin, and zinc are also converted into oxides and sulphides when heated 
in sulphurous acid gas ; S0 2 + Zn 3 = ZnS + 2ZnO , 

Sulphites. — The acid character of sulphurous acid is rather feeble, 
although stronger than that of carbonic acid. There is much general re- 
semblance between the sulphites and carbonates, in point of solubility, 
the sulphites of the alkali metals being the only salts of sulphurous acid 
which are freely soluble in water. Sulphurous acid, H 2 S0 3 being dibasic 
like carbonic, forms two classes of salts, the normal sulphites (for example, 
sodium sulphite, !N"a 2 S0 3 ), and acid sulphites (as hydropotassic sulphite, 
KHS0 3 ). 

Sodium sulphite is extensively manufactured for the use of the paper- 
maker, who employs it as an antichlore for killing the bleach, that is, 
neutralising the excess of chlorine after bleaching the rags with chloride 
of lime and sulphuric acid (see p. 156) — 

Na 2 S0 3 + H 2 + Cl 2 = :Na 2 S0 4 + 2HC1. 

* Qelov, sulphur. 



202 SULPHURIC ACID. 

It is prepared by passing sulphurous acid gas over damp crystals of 
sodium carbonate, wben carbonic acid gas is expelled, and sodium sulphite 
formed, which is dissolved in water and crystallised. It forms oblique 
prisms, having the composition ISTa^Og'TAq., which effloresce in the air, 
becoming opaque, and slowly absorbing oxygen, passing into sodium sul- 
phate (Na 2 S0 4 ). Its solution is slightly alkaline to test-papers. 

For the manufacture of sodium sulphite the sulphurous acid gas is 
obtained either by the combustion of sulphur or by heating sulphuric 
acid with charcoal ; 2H 2 S0 4 + C = 2H 2 + C0 2 + 2S0 2 . 

The carbon dioxide of course will not interfere with this application of 
the sulphur dioxide. 

Sulphuric Acid. 

H. 2 S0 4 = 98 parts by weight. 

144. More than four centuries ago, the alchemist Basil Valentine sub- 
jected green vitriol, as it was then called (sulphate of iron), to distillation, 
and obtained an acid liquid which he named oil of vitriol. The process 
discovered by this laborious monk is even now in use at Nordhausen in 
Saxony, and the Nordhausen oil of vitriol is an important article of com- 
merce. The crystals of ferrous sulphate (FeS0 4 7H 2 0) are exposed to the 
air so that they may obsorb oxygen, and become converted into the basic 
ferric sulphate ; 6FeS0 4 + 3 = 2Fe 2 (S0 4 ) 3 . Fe 2 3 . 

This salt is partially dried, and distilled in earthenware retorts, when 
a mixture of sulphuric acid and sulphuric anhydride distils over, and is 
sent into commerce as Nordhausen or fuming sulphuric acid Fe 2 (S0 4 ) 3 
+ 2H 2 = Fe 2 3 + 2H 2 S0 4 + S0 3 . The ferric oxide (Fe 2 3 ) which is left 
in the retorts, is the red powder known as colcothar, which is used for 
polishing plate glass and metals. 

The green vitriol employed for preparing the Nordhausen acid is obtained from 
iron pyrites (FeS 2 ). A particular variety of this mineral, white pyrites (or efflores- 
cent pyrites), when exposed to moist air, undergoes oxidation, yielding ferrous 
sulphate and sulphuric acid ; FeS 2 + H 2 + 7 — FeS0 4 + H 2 S0 4 . 

Large masses of this variety of pyrites in mineralogical cabinets may often be 
seen broken up into small fragments, and covered with an acid efflorescence of ferrous 
sulphate from this cause. Ordinary iron pyrites is not oxidised by exposure to the 
air unless it be first subjected to distillation in order to separate a portion of the 
sulphur which it contains. 

Fuming sulphuric acid is now made in England by dissolving sulphuric anhydride 
in about twice its weight of oil of vitriol. In order to procure the sulphuric 
anhydride, oil of vitriol (H 2 S0 4 ) is decomposed by a high temperature into steam, 
sulphurous acid gas, and oxygen ; the vapour of water is removed by passing the 
gases through oil of vitriol, and the S0 2 and are caused to combine by passing them 
over hot platinised asbestos. The fuming acid is kept in vessels of tinned iron 
upon which it has no action. 

The Nordhausen acid is readily distinguished from English sulphuric 
acid by its fuming in the air when the bottle is opened. This is due to 
the escape of a little vapour of sulphuric anhydride. It is heavier than 
the English acid, its specific gravity being 1*9. It is chiefly used for 
dissolving indigo in preparing the Saxony . blue dye, also in making 
alizarine, and is a convenient source of the anhydride ; for if it be gently 
heated in a retort, the anhydride is disengaged, and may be condensed 
in silky crystals in a receiver kept cool by ice, whilst ordinary sulphuric 
acid (H 2 S0 4 ) is left in the retort. 



MANUFACTURE OF OIL OF VITEIOL. 203 

An acid containing 40 or 50 per cent, of dissolved sulphuric anhydride 
is solid at ordinary temperatures, whilst that containing 60 or 70 percent, 
is liquid even below 0° C. 

The process adopted at Nordhausen, though simple in theory, is expen- 
sive, on account of the consumption of fuel and the breaking of the retorts, 
so that the price of the acid, compared with that of English manufacture, 
is very high. 

The first step towards the discovery of our present process was also 
made by Valentine, when he prepared his oleum sulpliuris per campanum, 
by burning sulphur under a bell-glass over water, and evaporating the 
acid liquid thus obtained. The same experimenter also made a very im- 
portant advance when he burnt a mixture of sulphur, antimony sulphide, 
and nitre under a bell-glass placed over water ; but it was not until 
the middle of the 18th century that it was suggested by some French 
chemists to burn the sulphur and nitre alone over water ; a process by 
which the acid appears actually to have been manufactured upon a pretty 
large scale. The substitution of large chambers of lead for glass vessels 
by Dr. Roebuck was a great improvement in the process, and about the 
year 1770 the preparation of the acid formed au important branch of 
manufacture ; since then the process has been steadily improving until, 
at the present time, upwards of 100,000 tons are annually consumed in 
Great Britain, and a very large quantity is exported. The diminution in 
the price of oil of vitriol well exhibits the progress of improvement in its 
production, for the original oil of sulphur appears to have been sold for 
about half-a-crown an ounce, and that prepared by burning sulphur with 
nitre in glass vessels at the same price per pound ; but when leaden 
chambers were introduced, the price fell to m a shilling per pound, and at 
present oil of vitriol can be purchased at the rate of five farthings per 
pound. 

The description of the present process of manufacture will be best 
understood after a consideration of the chemical changes upon which it 
depends, 

It has been seen that when sulphur is burnt in air, sulphur dioxide is 
the chief product. When this acts upon nitric acid, in the presence of 
water, sulphuric acid and nitric oxide are formed — 

3S0 2 + 2KN"O s + 2H 2 = 3H 2 S0 4 + 2NO . 

Mtric oxide, in contact with air, combines with its oxygen to form 
nitric peroxide (N0 2 ). 

If nitric peroxide is brought into contact with sulphurous acid gas and 
water, it is again converted into nitric oxide, with formation of sulphuric 
acid; N0 2 + S0 2 + H 2 = M) + H 2 S0 4 . 

It appears, therefore, that nitric oxide may be employed to absorb 
oxygen from the air, and to convey it to the sulphur dioxide, so that 
theoretically, an unlimited quantity of sulphur might be converted into 
sulphuric acid by a given quantity of nitric oxide, with a sufficient supply 
of air and water. 

To illustrate these important chemical principles of the manufacture of sulphuric 
acid, the following experiments may be performed : — 

1. A quart bottle of nitric oxide (p. 141), is placed mouth to mouth with a pint 
bottle of oxygen, when both bottles will be filled with the red nitric peroxide. 

2. The quart bottle of this red gas is placed mouth to mouth with a quart bottle 



204 



THEORY OF PRODUCTION OF OIL OF VITRIOL. 




Fig. 205. 



of sulphurous acid gas (fig. 205), when the red colour will soon disappear, and the 
sides of the bottles will be covered with a crystalline substance formed by the reaction 

between the nitric peroxide, the sulphur dioxide, and 
the small quantity of water present in the gases — 
2S0. 2 + 3N0 2 + H 2 = 2(NOHS0 4 ) + NO . 
3. A little water is shaken round in the bottles, 
when the crystals will be dissolved with effervescence, 
evolving nitric oxide and peroxide, and producing 
sulphuric acid — 

2(NOHS0 4 ) + H 2 = NO + N0 2 + 2H 2 S0 4 . 

In the presence of abundance of water this crystal- 
line compound is not produced, as may be shown by 
the following modification of the experiment. 

A large glass flask or globe* (A, fig. 206) is fitted 
with a cork, through which are passed — 

(a) A tube connected with a flask (D) containing copper and stroug sulphuric acid, 
for evolving sulphurous acid gas ; 

(b) A tube connected with a flask (B) containing copper and diluted nitric acid 
(sp. gr. 1 '2) for supplying nitric oxide ; 

(c) A tube proceeding from a small flask (E) containing water. 

On applying a gentle heat to the flask containing nitric acid and copper, the nitric 
oxide passes into the globe and combines with the oxygen of the air, filling the 

globe with red nitric peroxide. 
The nitric oxide flask may then 
be removed. Sulphurous acid gas 
is then generated by heating the 
flask containing sulphuric acid 
and copper ; the sulphurous acid 
gas will soon decolorise the red 
nitric peroxide, the contents of the 
globe becoming colourless, and 
the crystalline compound form- 
ing abundantly on the sides ; the 
sulphur dioxide flask may then 
be removed. Steam is sent into 
the globe from the flask contain- 
ing water, when the crystalline 
compound will be dissolved, and 
sulphuric acid will collect at the 
bottom of the globe. If air be 
now blown into the globe, the 
nitric oxide will again acquire the 
red colour of nitric peroxide. 
If the experiment be repeated, the steam being introduced simultaneously with 
the sulphurous acid gas, no crystalline compound whatever will be formed, the 
sulphur dioxide being at once converted into sulphuric acid. 

Since the cork is somewhat corroded in this experiment, it is preferable to have 
the mouth of the flask ground and closed by a ground glass plate, perforated with 
holes for the passage of the tubes. The perforations are easily made by placing the 
glass plate flat against the wall and piercing it with the point of a revolving rat's- 
tail file dipped in turpentine ; the file is then gradually worked through the hole 
until the latter is of the required size. 

The process employed for the manufacture of English oil of vitriol will 
now be easily understood. 

A series of chambers is constructed of leaden plates, the edges of 
which are united by autogenous soldering (that is, by fusing their edges, 
without solder, which would be rapidly corroded by the acid vapours) ; 
the leaden chambers are supported and strengthened by a framework of 
timber (fig. 207). 

* The operation is, of course, more striking if oxygen is employed instead of air, the globe 
in fig. 206 being filled with oxygen by displacement at the commencement. 




Fig. 206. — Preparation of sulphuric acid. 



REACTIONS IN THE VITRIOL CHAMBERS. 



205 



The sulphurous acid gas is generated by burning sulphur or iron pyrites 
in a suitable furnace (A) adjoining the chambers, and so arranged that 
the gas produced may be mixed with about the proper quantity of air to 
furnish the oxygen required for its conversion into sulphuric acid. 

Nitric acid vapour is evolved from a mixture of sodium nitrate and oil 
of vitriol (see p. 136) contained in an iron pan which is heated by the 
combustion of the sulphur, so that the nitric acid is carried into the cham- 
bers with the current of sulphurous acid gas and air. 



1^1 ia ci ra 




Fig. 207. —Sulphuric acid chambers. 

Water covers the floor of the chambers to the depth of about 2 inches, 
and jets of steam are introduced at different jarts from an adjacent 
boiler (B). 

The sulphurous acid gas acts upon the nitric acid vapour, in the presence 
of the water, forming nitric oxide and sulphuric acid, which rains down 
into the water on the floor of the chambers — 



3S0 9 + 2HXCL + 



2H 2 



= 2X0 + 3H SO, 



If this nitric oxide were permitted to escape from the chambers, and a 
fresh quantity of nitric acid vapour introduced to oxidise another portion 
of sulphur dioxide, it is evident that 2 molecules (170 parts by weight) of 



206 EE ACTIONS IN THE VITRIOL CHAMBERS. 

sodium nitrate would be required to furnish the nitric acid for the con- 
version of 3 atoms (96 parts by weight) of sulphur, whereas, in practice, 
6 parts by weight only of nitrate are employed for 96 parts of sulphur. 

For the nitric oxide (NO) at once acquires oxygen from the air ad- 
mitted together with the sulphurous acid gas, and becomes nitric peroxide 
(-N~0 2 ), which oxidises more sulphurous acid gas in the presence of water, 
converting it into sulphuric acid — 

S0 2 + N0 2 + H 2 == H 2 S0 4 + NO . 

A great reduction in the volume of the gas in the chamber thus takes 
place (2 volumes S0 2 and 2 volumes N0 2 yielding 2 volumes NO), so that 
there is room for the introduction of a fresh quantity of the mixture of 
sulphurous acid gas and air from the furnace, upon which the nitric oxide 
acts as before, taking up the oxygen from the air and handing it over to 
the sulphur dioxide, in the presence of water, to produce a fresh supply of 
sulphuric acid. 

But the nitrogen of the air takes no part in these changes ; and since 
the oxygen consumed in converting the sulphur into sulphuric acid is 
accompanied by four times its volume of nitrogen, a very large accumula- 
tion of this gas takes place in the chambers, and provision must be made 
for its removal in order to allow space for those gases which take part in 
the change. The obvious plan would appear to be the erection of a simple 
chimney for the escape of the nitrogen at the opposite end of the chamber 
to that at which the sulphurous acid gas and air enter it : and this plan 
was formerly adopted, but the nitrogen carries off with it a portion of the 
nitric oxide which is so valuable in the chamber, and to save this the 
escaping nitrogen is now generally passed through a leaden chamber (Gay- 
Lussac's tower; (C) filled with coke, over which oil of vitriol is allowed to 
trickle : the oil of vitriol absorbs the nitric oxide,* and flows into a cistern 
(D), from which it is forced up, by the pressure of steam, to the top of 
another chamber (Glover's tower) (E) arranged with shelves in cascade 
or packed with flints, through which the hot sulphurous acid gas and air 
are made to pass as they enter, when they take up the nitrous anhydride 
from the oil of vitriol, and carry it with them into the chamber. 

Before the introduction of this plan it required a quantity of sodium 
nitrate amounting to ^th or y^-th of the weight of the sulphur to convert 
it into sulphuric acid, whereas about ^th, or even less, is now often 
made to suffice. 

In the vitriol chambers represented in fig. 207, the mixture of gases passing from 
the first square chamber into the second contains a large excess of sulphurous acid gas, 
which is oxidised and converted into sulphuric acid by the nitric acid flowing down 
the cascade represented at the entrance to the second chamber. The mixture of 
sulphuric acid with excess of nitric acid and other oxides of nitrogen which is thus 
formed, is made to pass back into the first chamber, in order to be deoxidised by the 
excess of sulphurous acid gas. It is thence conducted by a pipe, not shown in the 
figure, into the middle chamber of much larger size, where the principal reaction 
between the sulphurous acid gas, the nitric oxide gas, and the oxygen of the air, 
takes place. The reaction is completed during the passage through the two last 
small chambers, and the gases are finally cooled by passing through a chamber sur- 
rounded with cold water before being discharged into the Gay-Lussac's tower 0. 

The sulphuric acid is allowed to collect on the floor of the chamber 
until it has a specific gravity of about 1 '6, and contains 70 per cent, of oil 

* Strictly speaking, it is nitrous anhydride, N 2 3 , which is absorbed by the H 2 S0 4 , 
there being still enough to convert 2NO into N 2 3 . 



.COMMERCIAL VARIETIES OF SULPHURIC ACID. 207 

of vitriol (H 2 S0 4 ). If it were allowed to become more concentrated than 
this, it would absorb some of the oxides of nitrogen in the chamber, so that 
it is now drawn off. 

This acid is quite strong enough for some of the applications of sul- 
phuric acid, particularly for that which consumes the largest quantity in 
this country, viz., the conversion of common salt into sodium sulphate as 
a preliminary step in the manufacture of carbonate of soda. To save the 
expense of transporting the acid for this purpose, the vitriol chambers 
form part of the plant of the alkali works. 

To convert this weak acid into the ordinary oil of vitriol of commerce, 
it is run off into shallow leaden pans set in brickwork, and supported on 
iron bars over the flue of a furnace, where it is heated until so much 
water has evaporated that the specific gravity of the acid has increased to 
1 '72. The concentration cannot be carried further in leaden pans, because 
the strong acid acts upon the lead, and converts it into sulphate— 
2H 2 S0 4 + Pb = PbS0 4 + 2H 2 + S0 2 .' 

The concentration of the acid is now often effected by high pressure 
steam passing through leaden worms immersed in the acid which is con- 
tained in wooden vats lined with lead. 

The acid of 1*72 sp. gr. contains about 80 per cent, of true oil of vitriol, 
and is largely employed for making superphosphate of lime, and in other 
rough chemical manufactures. It is technically called brown acid, having 
acquired a brown colour from organic matter accidentally present in it. 

To convert this brown acid into commercial oil of vitriol, it is boiled 
down, either in glass retorts or platinum stills, when water distils over, 
accompanied by a little sulphuric acid, and the acid in the retort becomes 
colourless, the brown carbonaceous matter being oxidised by the strong 
sulphuric acid, with formation of carbonic and sulphurous acid gases. 
When dense white fumes of oil of vitriol begin to pass over, showing 
that all the superfluous water has been expelled, the acid is drawn off by 
a siphon. 

The very diluted acid which distils off is employed instead of water on 
the floor of the leaden chamber. 

The cost of the acid is very much increased by this concentration. It cannot be 
conducted in open vessels, partly on account of the loss of sulphuric acid, partly be- 
cause concentrated sulphuric acid absorbs moisture from the open air even at the 
boiling-point. The loss by breakage of the glass retorts is very considerable, although 
it is reduced as far as possible by heating them in sand, and keeping them always at 
about the same temperature by supplying them with hot acid. But the boiling- 
point of the concentrated acid is very high (640° F. ), and the retorts consequently 
become so hot that a current of cold air or an accidental splash of acid will frequently 
crack them at once. Moreover the acid boils with succussion or violent bumping, 
caused by sudden bursts of vapour, which endanger the safety of the retort. 

With platinum stills the risk of fracture is avoided, and the distillation may be 
conducted more rapidly, the brown acid (sp. gr. 1 72), being admitted at the top, 
and the oil of vitriol (sp. gr. l - 84) drawn .off by a platinum siphon from the bottom 
of the still, which is protected from the open fire by an iron jacket. But since a 
platinum. still costs £2000 or £3000, the interest upon its value increases the cost of 
production of the acid. 

When the perfectly pure acid is required, it is actually distilled over so as to leave 
the solid impurities (sulphate of lead, &c. ) behind in the retort. Some fragments 
of rock crystal should be introduced into the retort to moderate the bursts of vapour, 
and heat applied by a ring gas-burner with somewhat divergent jets. 

Divested of working details, this most important chemical manufacture 
may be thus described : — 



208 PROPERTIES OF SULPHURIC ACID. 

A mixture of sulphurous acid gas, air, steam, and a little vapour of 
nitric acid, is introduced into a leaden chamber containing a layer of 
water. The nitric acid is reduced by the sulphurous acid gas to the state 
of nitric oxide (NO), which takes up oxygen from the air (forming N0 2 ), 
and gives it to the sulphurous acid gas, which it converts into sulphuric 
acid. This is absorbed by the water, forming diluted sulphuric acid, 
which is concentrated by evaporation first in leaden pans, and afterwards 
in glass retorts or platinum stills. The nitric oxide becomes the vehicle 
by which the oxygen of the air is transferred to the sulphur dioxide. 

Properties of oil of vitriol. — The properties of concentrated sulphuric 
acid are very characteristic. Its great weight (sp. gr. 1 -842), freedom 
from odour, and oily appearance, distinguish it from any other liquid 
commonly met with, which is fortunate, because it is difficult to preserve 
a label upon the bottles of this powerfully corrosive acid. Although, if 
absolutely pure, it is perfectly colourless, the ordinary acid used in the 
laboratory has a peculiar grey colour, due to traces of organic matter. 
Its high boiling-point (640° F.) has been already noticed ; and although 
its vapour is perfectly transparent in the vessel in which the acid is boiled, 
as soon as it issues into the air it condenses into voluminous dense clouds 
of a most irritating description. Even a drop of the acid evaporated in 
an open dish will fill a large space with these clouds. Oil of vitriol 
solidities when cooled to about - 30° F., but the acid once solidified 
requires a much higher temperature to liquefy it again. Oil of vitriol 
rapidly corrodes the skin and other organic textures upon which it falls, 
usually charring or blackening them at the same time. Poured upon a 
piece of wood, the latter speedily assumes a dark brown colour ; and if a 
few lumps of sugar be dissolved in a very little water, and stirred with 
oil of vitriol, a violent action takes place, and a semi-solid black mass is 
produced. This property of sulphuric acid is turned to account in the 
manufacture of blacking, in which treacle and oil of vitriol are employed. 
These effects are to be ascribed to the powerful attraction of oil of vitriol 
for water. Woody fibre (C 6 H 10 O 5 ) (which composes the bulk of wood, 
paper, and linen), and sugar (C 12 H 22 O n ), may be regarded, for the pur- 
pose of this explanation, as composed of carbon associated with 5 and 11 
molecules of water, and any cause tending to remove the water would 
tend to eliminate the carbon. 

The great attraction of this acid for water is shown by the high tem- 
perature (often exceeding the boiling-point of water) produced on mixing 
oil of vitriol with water, which renders it necessary to be careful in dilut- 
ing the acid. 

The water should be placed in a jug, and the oil of vitriol poured into it in a thin 
stream, a glass rod being used to mix the acid with the water as it flows in. Ordi- 
nary oil of vitriol becomes turbid when mixed with water, from the separation of 
sulphate of lead (formed from the evaporating pans), which is soluble in the concen- 
trated, but not in the diluted acid, so that if the latter be allowed to stand for a few 
hours, the sulphate of lead settles to the bottom, and the clear acid may be poured 
off free from lead. Dilated sulphuric acid has a smaller bulk than is occupied by the 
acid and water before mixing. 

The heat evolved on combining one molecular weight of H 2 S0 4 with one of water 
amounts to 69 7 centigrade units. Decreasing quantities of heat are evolved for 
successive additions of water, until 120 molecules of water have been added. 

Even when largely diluted, sulphuric acid corrodes textile fabrics very 
rapidly, and though the acid be too dilute to appear to injure them at 



PROPERTIES OF SULPHURIC ACID. 



209 



first, it will be found that the water evaporates by degrees, leaving the 
acid in a more concentrated state, and the fibre is then perfectly rotten. 
The same result ensues at once on the application of heat ; thus, if charac- 
ters be written on paper with the diluted acid, they will remain invisible 
until the paper is held to the fire, when the acid will char the paper, and 
the writing will appear intensely black. 

If oil of vitriol be left exposed to the air in an open vessel, it very soon 
increases largely in bulk from the absorption of water, and a flat dish of 
oil of vitriol under a glass shade (fig. 
208) is frequently employed in the 
laboratory for drying substances with- 
out the assistance of heat. The drying 
is of course much accelerated by 
placing the dish on the plate of an 
air-pump, and exhausting the air from 
the shade, so as to effect the drying 
in vacuo. It will be remembered 
also that oil of vitriol is in constant 
use for drying gases. 

At a red heat, the vapour of oil of vitriol is decomposed into water, 
sulphurous acid gas, and oxygen ; H 2 S0 4 = H 2 + S0 2 + . 

When sulphur is boiled with oil of vitriol, the latter gradually dissolves 
the melted sulphur, converting it into sulphurous acid gas — - 

S + 2H 2 S0 4 = 3S0 2 + 2H 2 0. 

All ordinary metals are acted upon by concentrated sulphuric acid when 
heated, except gold and platinum (the latter does not quite escape when 
long boiled with the acid), the metal being -oxidised by one portion of 
the acid, which is thus converted into sulphur dioxide, the oxide reacting 
with another part of the sulphuric acid to form a sulphate. Thus, when 
silver is boiled with strong sulphuric acid, it is converted into sulphate of 




Fig. 208. — Drying over oil of vitriol. 



silver, which is soluble in hot water — 
Ag 2 + 2H 2 S0 4 = Ag 2 S0 4 



2H 2 



+ SO, 



Should the silver contain any gold, it is left behind in the form of a dark 
powder. Sulphuric acid is extensively employed for the separation or 
parting of silver and gold. This acid is also employed for extracting gold 
from copper ; and when sulphate of copper is manufactured by dissolving 
that metal in sulphuric acid (see p. 199), large quantities of gold are 
sometimes extracted from the accumulated residue left undissolved by the 
acid. If the sulphuric acid contains nitric acid, it dissolves a considerable 
quantity of gold, which separates again in the form of a purple powder 
when the acid is diluted with water, the sulphate of gold formed being 
reduced by the nitrous acid when the solution is diluted. 
' Some of the uses of sulphuric acid depend upon its specific action on 
certain organic substances, the nature of which has not yet been clearly 
explained. Of this kind is the conversion of paper into vegetable parch- 
ment by immersion in a cool mixture of two measures of oil of vitriol and 
one measure of water, and subsequent washing. The conversion is not 
attended by any change in the weight of the paper. 

Sulphuric acid forms definite combinations with water. By evaporating 
diluted sulphuric acid in vacuo at 212° F., an acid is left which has the 
(sp. gr. 1'63). If this acid be evaporated in 





composition H 2 SO 



,2H 2 



210 



SULPHURIC ANHYDRIDE. 




air at 400° F., as long as steam escapes, the remaining acid has the com- 
position H 2 S0 4 .H 2 (sp. gr. 1*78). This acid is called glacial sulphuric 
acid, because it solidifies to a mass of ice-like crystals at 47° F. It is 
sometimes sold instead of H 2 S0 4 , and may be known by its freezing 
in winter. 

145. Anhydrous sulphuric acid or sulphuric anhydride (SO 3 = 80). — 
Sulphurous acid and oxygen gases combine to form sulphuric anhydride 
(S0 3 ) when passed through a tube containing heated platinum or certain 
metallic oxides, such as those of copper and chromium, the action of 
which in promoting the combination is not thoroughly understood. 

The combination may be shown by passing oxygen from the tube A (fig. 209) 
connected with a gas-holder, through a strong solution of sulphurous acid (B), so 

that it may take up a quantity of that gas, 
afterwards through a tube (C) containing 
pumice-stone soaked with oil of vitriol, to 
remove the water, and then through a bulb 
(D) containing platinised asbestos (see p. 
143). The mixture of the gases issuing 
into the air is quite invisible, but when the 
bulb is gently heated, combination takes 
place, and dense white clouds are formed 
in the air, from the combination of the 
sulphuric anhydride (S0 3 ) produced, with 
the atmospheric moisture. 

Fig. 209. Sulphuric anhydride forms a white 

mass of crystals resembling asbestos ; 
it fumes when exposed to air, since it emits vapour which condenses the 
moisture of the air, and it soon deliquesces from absorption of water, 
becoming sulphuric acid ; S0 3 + H 2 = H 2 S0 4 . When thrown into 
water it hisses like red hot iron, from the sudden formation of steam. It 
fuses at 65° F., and boils at 110° F. The vapour is decomposed, as men- 
tioned above, into sulphurous acid gas and oxygen, when passed through 
a red hot tube. Phosphorus burns in its vapour, combining with the 
oxygen and liberating sulphur. Baryta glows when heated in the vapour 
of sulphuric anhydride, and combines with it to form barium sulphate. 

Sulphuric anhydride is capable of combining with olefiant gas (C 2 H 4 ) 
and similar hydrocarbons, and absorbs these from mixtures of gases. In 
the analysis of coal gas, a fragment of coke wetted with JSTordhausen 
sulphuric acid is passed up into a measured volume of the gas standing 
over mercury to absorb these illuminating hydrocarbons. 

An interesting method of obtaining the sulphuric anhydride consists 
in pouring 2 parts by weight of oil of vitriol over 3 parts of phosphoric 
anhydride, contained in a retort cooled in ice and salt, and afterwards 
distilling at a gentle heat, when the phosphoric anhydride retains water, 
and the S0 3 may be condensed in a cooled receiver. 

When oil of vitriol is converted into vapour, its molecular weight (98 
parts) is found to yield 4 volumes of vapour instead of 2, which is 
explained by a dissociation or temporary decomposition of the molecule 
of H 2 S0 4 into H 2 (2 volumes), and S0 3 (2 volumes). On cooling these 
recombine to form H 2 S0 4 . . 

146. Sulphates — Action of sulphuric acid, upon metallic oxides. — At 
common temperatures sulphuric acid is capable of displacing all other 
acids from their salts ; many cases will be remembered in which this 
power of sulphuric acid is turned to account. 



SULPHATES. 



211 



So great is the acid energy of sulphuric acid, that when it is allowed 
to act upon an indifferent or acid metallic oxide, it causes the separation 
of a part of the oxygen, and reacts with the basic oxide so produced. 
Advantage is sometimes taken of this circumstance for the preparation of 
oxygen; for instance, when manganese dioxide is heated with sulphuric 
acid, sulphate of manganese is produced, and oxygen disengaged — 

Mn0 2 + H 2 S0 4 = MnS0 4 + + H 2 0. 

Again, if chromic anhydride he treated in the same way, chromic sulphate 
will be produced, with liberation of oxygen — 

2Cr0 3 + 3H 2 S0 4 = Cr 2 .3S0 4 + 3 + 3H 2 . 

A mixture of potassium dichromate (K 2 0.2Cr0 3 ) and sulphuric acid is 
sometimes used as a source of oxygen. 

Sulphuric acid is a dibasic acid, that is, it contains two atoms of 
hydrogen which may be replaced by a metal. In normal sulphates, both 
atoms of H are so replaced, as in K 2 S0 4 , the normal potassium sulphate. 
When only a part of the H is replaced, acid sulphates are produced; thus 
KHS0 4 is acid potassium sulphate, which is very useful in blowpipe and 
rnetallurgic chemistry, because, when heated, it yields normal potassium 
sulphate and sulphuric acid ; 2KHS0 4 = K 2 S0 4 + H 2 S0 4 . When the 
two atoms of H in H 2 S0 4 are replaced by different metals, double sul- 
phates are formed ; potassium-alum, KA1(S0 4 ) 2 , is an example of this 
class, in which one-fourth of the H in 2H 2 S0 4 is replaced by potassium, 
and the other three atoms by triatomic aluminium. 

The following table exhibits the composition of the sulphates most 
frequently met with : — 



Chemical Name. 


Common Name. 


Formula. 


Potassium sulphate 


Sal polychrest 


K 2 S0 4 


Sodium sulphate 


Glauber's Salt 


Na 9 SO 4 .10H 2 O 


Hydropotassic sulphate 




KHS0 4 


Ammonium sulphate 




(NH 4 ) 2 S0 4 


Barium sulphate 


Heavy spar 


BaS0 4 


Calcium sulphate 


Gypsum 


CaS0 4 .2H 2 


Magnesium sulphate 


Epsom salts 


MgS0 4 .7H 2 


Potassium-aluminium sulphate 


Potash -alum 


KA1(S0 4 ) 2 .12H 2 


Aluminium-ammoninm sulphate 


Ammonia-alum 


NH 4 A1(30 4 ) 2 .12H,0 


Potassium-chromium sulphate 


Chrome-alum 


KO(S0 4 ) 2 .12H 2 0" 


Ferrous sulphate j 


Green vitriol ) 
Copperas \ 


FeS0 4 .7H 2 


Manganous sulphate 




MnS0 4 .5H 2 


Zinc sulphate 


White vitriol 


ZuS0 4 .7H 2 


Lead sulphate 




PbS0 4 


Cupric sulphate ] 


Blue vitriol ) 
Blue stone \ 


CuS0 4 .5H 2 



In consequence of the tendency of sulphuric acid to break up into sul- 
phur dioxide and oxygen at a high temperature, most of the sulphates are 
decomposed by heat ; cupric sulphate, for example, when very strongly 
heated, leaves cupric oxide, whilst sulphur dioxide and oxygen escape ; 
CuS0 4 = CuO 4- S0 2 + 0. Ferrous sulphate is more easily decomposed ; 
2FeS0 4 = Fe 2 3 + S0 2 + S0 3 . 

The normal sulphates of potassium, sodium, barium, strontium, calcium, 



212 HYPOSULPHITE OF SODA. 

and lead are not decomposed by heat, and sulphate of magnesium is only 
partly decomposed at a very high temperature. 

When a sulphate of an alkali or alkaline earth metal is heated with char- 
coal, the carbon removes the whole of the oxygen, and a sulphide of the 
metal remains, thus — 

K 2 S0 4 {Potassium sulphate) + C 4 = K^S { p °tassium sulphide) + 4CO . 

Hydrogen, at a high temperature, effects a similar decomposition. 

Even at the ordinary temperature, calcium sulphate in solution is 
sometimes deoxidised by organic matter ; this may occasionally be noticed 
in well and river waters when kept in closed vessels ; they acquire a strong- 
smell of hydrosulphuric acid, in consequence of the conversion of a part 
of the calcium sulphate into sulphide by the organic constituents of the 
water, and the subsequent decomposition of the calcium sulphide by the 
carbonic acid present in the water. 

Acids containing Hydrogen, Sulphur, and Oxygen. 



Hyposulphurous (formerly hydrosulphurous), 
Sulphurous, .... 
Sulphuric, .... 

Thiosulphuric (formerly hyposulphurous), 
Dithionic, .... 

Trithionic, .... 
Tetrathionic, .... 
Pentathionic, .... 



H. 2 S0 4 



H,8 8 6 

h,s 4 o 6 

H 8 S 5 6 



147. Hyposulphurous or thiosulphuric acid* (H 2 S 2 3 ). — This acid has 
not been obtained in the separate state ; but many salts are known which 
are evidently derived from it, and such salts are called hyposulphites or 
tldosulphates. 

The sodium hyposulphite is by far the most important of these salts, 
being very largely employed in photography, and as a substitute for 
sodium sulphite as an antichlore. The simplest method of preparing it 
consists in digesting powdered roll sulphur with solution of sodium 
sulphite (Na 2 S0 3 ), when the latter dissolves an atom of sulphur and 
becomes hyposulphite (Na 2 S 2 3 ), which crystallises from the solution, 
when sufficiently evaporated, in fine prismatic crystals, having the 
formula Na 2 S 2 3 .5H 2 . 

On a large scale, sodium hyposulphite is more economically prepared 
from the calcium hyposulphite obtained by exposing the refuse (tank-waste 
or soda-waste) of the alkali works to the air for some days. This refuse 
contains a large proportion of calcium sulphide, which becomes converted 
into hyposulphite by oxidation ; 2CaS + 4 = CaS 2 3 -J- CaO . 

The hyposulphite is dissolved out by water, and the solution mixed 
with sodium carbonate, when calcium carbonate is precipitated and 
sodium hyposulphite remains in solution ; CaS 2 3 + Na 2 C0 3 = CaC0 3 
+ Na 2 S 2 8 . 

The most remarkable and useful property of the sodium hyposulphite 
is that of dissolving the chloride and iodide of silver, which are insoluble 
in water and most other liquids. 

On mixing a solution of silver nitrate with one of sodium chloride, a white 
precipitate of silver chloride is obtained, the separation of which is promoted by 
stirring the liquid; AgN0 3 + NaCl = AgCl + Na]Sr0 3 . The precipitate may be 

* 'Ttto, under, containing less oxygen than sulphurous acid. The name hyposulphurous 
acid is now often bestowed upon the acid H 2 S0 2 (p. 214). 



HYPOSULPHITE OF SODA. 213 

allowed to settle and washed twice or thrice by decantation. One portion of the 
silver chloride is transferred to another glass, mixed with water, and solution of 
sodium hyposulphite added by degrees. The silver chloride is very easily dissolved, 
yielding an intensely sweet solution, which contains the hyposulphite of sodium and 
silver, produced by double decomposition between the silver chloride and sodium 
hyposulphite ; AgCl + Na 2 S 2 3 = NaCl + NaAgS 2 3 . 

The sodium silver hyposulphite may be obtained in crystals from the solution. 

"When the silver chloride is acted on by a smaller proportion of the hyposulphite, 
another hyposulphite of sodium and silver is formed, which is very insoluble in 
water — 

2AgCl + 3Na 2 S 2 3 = Ag 2 Ka 4 (S 2 3 ) 3 + 2NaCl . 

Hence the necessity for using a strong solution of the hyposulphite in fixing photo- 
graphic prints. 

If the other portion of the silver chloride be exposed to the action of light, and 
especially of direct sunlight, it assumes by degrees a dark slate colour, from the for- 
mation of silver subchloride, 4AgCl + H 2 = 2Ag 2 Cl + HC1 + HCIO . By treating this 
darkened silver chloride with sodium hyposulphite, as before, the unaltered silver 
chloride will be entirely dissolved, but the subchloride will be decomposed into 
monoehloride, which dissolves in the hyposulphite, and metallic silver, which is left 
in a very finely-divided state as a black powder ; Ag 2 Cl = AgCl + Ag. The application 
of these facts in photography is well illustrated by the following experiments : — A 
sheet of paper is soaked for a minute or two in a solution of 10 grains of common salt 
in an ounce of water contained in a flat dish. It is then dried, and soaked for three 
minutes in a solution of 50 grains of silver nitrate in an ounce of water. The paper 
thus becomes impregnated with silver chloride formed by the decomposition between 
the sodium chloride and the silver nitrate. It is now hung up in a dark place to dry. 
If a piece of lace, or a fern leaf, or an engraving on thin paper, with well-marked 
contrast of light and shade, be laid upon a sheet of the prepared paper, pressed down 
upon it by a plate of glass and exposed for a short time to sunlight, a perfect repre- 
sentation of the object will be obtained, those parts of the sensitive paper to which 
the light had access having been darkened by the formation of silver subchloride, 
whilst those parts which were protected from the light remain unchanged. 

But if this photographic print were again exposed to the action of light, it would 
soon be obliterated, the unaltered silver chloride in" the white parts being acted on 
by light in its turn. The print is therefore fixed by soaking it for a short time in a 
saturated solution of sodium hyposulphite, Avhich dissolves the white unaltered silver 
chloride entirely, and decomposes the subchloride formed by the action of light, 
leaving the black finely-divided metallic silver in the paper. The print should now 
be washed for two or three hours in a gentle stream of water, to remove all the silver 
hyposulphite, when it will be quite permanent. 

The power of sodium hyposulphite to dissolve silver chloride has also 
been turned to account for extracting silver from its ores in which it is 
occasionally present in the form of chloride. 

The behaviour of solution of sodium hyposulphite with powerful 
acids explains the circumstance that the hyposulphurous acid has not been 
isolated, for if the solution be mixed with a little diluted sulphuric or 
hydrochloric acid, it remains clear for a few seconds, and then becomes 
suddenly turbid from the separation of sulphur, at the same time evolving 
a powerful odour of sulphur dioxide, H 2 S 2 3 = H 2 + S + S0 2 . This 
disposition of the hyposulphurous acid to break up into sulphur dioxide 
and sulphur also explains the precipitation of metallic sulphides, which 
often takes place when sodium hyposulphite is added to the acid solutions 
of the metals. Thus, if an acid solution of antimonious chloride (obtained 
by boiling crude antimony ore (Sb 2 S 3 ) with hydrochloric acid) be added 
to a boiling solution of sodium hyposulphite, the sulphur, separated from 
the hyposulphurous acid, combines with the antimony to form a fine orange- 
red precipitate of antimonious sulphide (Sb 2 S 3 ), which is used in painting 
under the name of antimony vermilion. On the large scale, the solution 
of calcium hyposulphite obtained from the alkali waste is employed in 



214 DITHIONIC ACID. 

the preparation of antimony vermilion, as being less expensive than the 
sodium-salt. Lead hyposulphite dissolved in sodium hyposulphite is 
used as a hair-dye, depositing the black lead sulphide. 

When crystals of sodium hyposulphite are heated in the air, they 
first fuse in their water of crystallisation, then dry up to a white mass, 
which burns with a blue flame, leaving a residue of sodium sulphate. 
If heated out of contact with air, sodium pentasulphide will be left 
with the sodium sulphate 4(Na 2 S 2 3 5H 2 0) = 20H 2 O + 3Na 2 S0 4 + Na 2 S 5 . 

Some of the reactions of sodium hyposulphite become more intelligible 
when the salt is represented as sodium sulphate (Na 2 S0 4 ) in which an 
atom of sulphur has displaced an atom of oxygen (Na 2 S0 3 S). 

Hydrosulphurous acid* (H 2 S0 2 ). — When an aqueous solution of sulphurous acid is 
placed in contact with zinc, the metal is dissolved, forming a yellow solution of zinc 
hydrosulphite ; 2H 2 S0 3 + Zn 2 = Zn(HS0 2 ) 2 + Zn(OH) 2 . 

The solution bleaches organic colours, and reduces the salts of silver, mercury, and 
copper to the metallic state. It is very unstable, soon becoming colourless zinc 
hyposulphite ; Zn(HS0 2 ) 2 = ZnS 2 3 + H 2 0. 

The sodium hydrosulphite, NaHSO.,, is obtained by digesting zinc in solution of 
acid sulphite of sodium ; NaHS0 3 + Zn = ZnO + NaHS0 2 . 

It forms needle-like crystals very soluble in water, insoluble in strong alcohol, and 
becoming acid sulphite of sodium, NaHS0 3 , by absorption of oxygen from the air. 
By decomposing the sodium hydrosulphite with oxalic acid, hydrosulphurous acid is 
obtained as an orange-yellow unstable liquid. 

148. Hyposulphuric acid or dithionic acid (H 2 S 2 6 or HS0 3 ) has not at present 
acquired any practical importance. To prepare a solution of the acid, manganese 
dioxide in a state of fine division is suspended in water and exposed to a current 
of sulphurous acid gas, the water being kept very cold whilst the gas is passing. A 
solution of manganous hyposulphate is thus obtained ; 2S0 2 + Mn0 2 = MnS 2 6 . Some 
manganous sulphate is always formed at the same time ; S0 2 + Mn0 2 = MnS0 4 , and 
if the temperature be allowed to rise, this will be produced in large quantity. 

The solution containing the sulphate and hyposulphate is decomposed by solution 
of baryta (baryta- water), when manganous oxide is precipitated, together with barium 
sulphate, and barium hyposulphate is left in solution. To the filtered solution 
dduted sulphuric acid is carefully added until all the barium is precipitated as 
sulphate, when the solution of hyposulphuric acid is filtered off and evaporated in 
vacuo over oil of vitriol. It forms a colourless inodorous liquid, which is decomposed 
when heated, into sulphuric acid and sulphur dioxide; H 2 S 2 6 = H 2 S0 4 + S0 2 . 
Oxidising agents (nitric acid, chlorine, &c. ) convert it into sulphuric acid. 

The hyposulphates are not of any practical importance ; they are all soluble, and are 
decomposed by heat, leaving sulpiiates, and evolving sulphur dioxide. 

149. Trithionic acid (H 2 S 3 O fi ) or sulphuretted hyposulphuric acid, is also a prac- 
tically unimportant acid. It is prepared from the potassium trithionate which is 
formed by boiling a strong solution of acid sulphite of potassium with sulphur until 
the solution becomes colourless, and filtering the hot solution from any undissolved 
sulphur; 6KHS0 3 + S = 2K 2 S 3 6 + K 2 S0 3 + 3H 2 0. The solution deposits potassium 
trithionate in prismatic crystals. By dissolving these in water, and decomposing 
the solution with perchloric acid, the potassium is precipitated as perchlorate, and a 
solution of trithionic acid is produced, from which the acid has been obtained in 
crystals. It is, however, very unstable, being easily resolved into sulphur dioxide, 
sulphuric acid, and free sulphur — ■ 

H 2 S 3 6 = H 2 S0 4 + S0 2 + S. 

150. Tetrathionic acid (H 2 S 4 6 ) is rather more stable than the preceding acid, 
though equally devoid of practical importance. It is formed when barium hypo- 
sulphite, suspended in a little water, is treated with iodine, when the tetrathionate 
is obtained in crystals ; 2(BaS 2 3 )' + I 2 = Bal 2 + BaS 4 6 . 

By exactly precipitating the barium from a solution of the tetrathionate by addition 
of diluted sulphuric acid, the solution of tetrathionic acid may be obtained. When 

* Often called hyposulphurous acid. Bernthsen gives the formula of the acid as 
H 2 S 2 4 , and that of the sodium salt as Na 2 S 2 4 . 



BISULPHIDE OF CARBON. 



215 



the solution is boiled, it is decomposed into sulphuric acid, sulphur dioxide, and 
free sulphur ; H 2 S 4 6 = H 2 S0 4 + S0 2 + S 2 . 

When solution of ferric chloride is added to sodium hyposulphite, a fine purple 
colour is at first produced, which speedily vanishes, leaving a colourless solution. 
The purple colour appears to be due to the formation of the ferric hyposulphite, which 
speedily decomposes, the ultimate result being expressed by the equation Fe 2 Cl 6 
+ 2(Na 9 S 2 3 ) = Na 2 S 4 6 + 2FeCl 2 + 2NaCl . 

151. Pentathionic acid (H 2 S 5 6 ) possesses some interest as resulting from the action 
of sulphuretted hydrogen upon sulphur dioxide, when much sulphur is deposited, 
and pentathionic acid remains in solution; 3H 2 S + 4S0 2 = H 2 S 5 6 + 2H 2 + S 2 . To 
obtain a concentrated solution of the acid, sulphuretted hydrogen and sulphur dioxide 
are passed alternately through the same portion of water until a large deposition of 
sulphur has taken place. This is allowed some hours to settle ; the clear liquid 
poured off and the solution concentrated by evaporation, first over a water-bath, and 
finally, in vacuo, over oil of vitriol ; for a concentrated solution of pentathionic acid 
is decomposed by heat into sulphuric acid and sulphur dioxide, with separation of 
sulphur; H 2 S 5 6 = H 2 S0 4 + S0 2 + S 3 . 

Per sulphuric acid is the name given by Berthelot to a crystalline compound, S 2 7 
formed from S0 2 and under the influence of electricity of high tension. 

Bisulphide of Carbon or Carbon Disulphide. 

CS 2 = 76 parts by weight. 

152. This very important compound (also called bisulplmret of carbon) 
is found in small quantity among the products of destructive distillation 
of coal, and is very largely manufactured for use as a solvent for sulphur, 
phosphorus, caoutchouc, fatty matters, &c. It is one of the few compounds 
of carbon which can be obtained by the direct union of their elements, 
and is prepared by passing vapour of sulphur over charcoal heated to 
redness. It is remarkable that no heat is evolved in this act of combination. 

In small quantity carbon sulphide is easily prepared in a tube of German glass 
(combustion-tube) about two feet long and half an inch in diameter (fig. 210). 




Fig. 210. 

This tube is closed at one end, and a few fragments of sulphur dropped into it, so 
as to occupy two or three inches. The rest of the tube is filled up with small frag- 
ments of recently calcined wood charcoal. The tube is placed in a combustion- 
furnace, and its open end connected by a perforated cork with a glass tube, which 
dips just below the surface of water contained in a bottle placed in a vessel of very 
cold water. That part of the tube which contains the charcoal is first surrounded 
with red hot charcoal, and when it is heated to redness a little red hot charcoal is 
placed near the end containing the sulphur (hitherto protected by a sheet-iron screen), 
so that the vapour of sulphur may be slowly passed over the red hot charcoal. The 
disulphide being insoluble in water, and much heavier (sp. gr. 1'27), is deposited be- 
neath the water in the receiver. To purify the carbon disulphide from the water and the 
excess of sulphur which is deposited with it, the water is carefully drawn off with a 
small siphon, the disulphide transferred to a flask, and a few fragments of calcium 
chloride dropped into it to absorb the water. A bent tube connected with a Liebig's 



216 



PREPARATION OF BISULPHIDE OF CARBON. 




Fig. 211. 



condenser, or with a worm, is attached to the flask (fig. 211) by a perforated cork, 
and the flask is gently heated in a water-bath, when the carbon disulphide is 
distilled over as a perfectly colourless liquid. The inflammability of the disulphide 
renders great care necessary. 

On a large scale, a fire-clay or cast-iron 
retort is filled with fragments of charcoal 
and heated to redness, pieces of sulphur 
being occasionally dropped in through an 
earthenware tube passing to the bottom of 
the retort. "When very large quantities 
are made, coke is employed, and the 
vapour of sulphur is obtained from iron 
pyrites. The carbon disulphide is pos- 
sessed of some very remarkable properties : 
it is a very brilliant liquid, the light 
passing through which at certain angles 
is partly decomposed into its component 
coloured rays before it reaches the eye. 
These properties are dependent upon its high refractive and dispersive 
powers, which are turned to great advantage in optical experiments, 
especially in spectrum analysis, where the rays emanating from a 
coloured flame are analysed by passing them through a prismatic bottle 
filled with carbon disulphide. It is also highly diathermanous, that is, 
it allows rays of heat to pass through it with comparatively little loss, so 
that if it be rendered opaque to light by dissolving iodine in it, the rays 
of light emanating from a luminous object may be arrested, whilst the 
calorific rays are allowed to pass. Carbon disulphide is a very volatile 
liquid, readily assuming the form of vapour at the ordinary temperature, 
and boiling at 11 8° '5 F. Its vapour, when diluted with air, has a very 
disgusting and exaggerated odour of sulphuretted hydrogen, but the smell 
at the mouth of the bottle is ethereal and not unpleasant if the disul- 
phide has been carefully purified. 

The rapid evaporation of carbon disulphide is, of course, productive of great cold. 
If a few drops be placed in a watch-glass and blown upon, they soon pass off in 
vapour, and the temperature of the glass is so reduced that some of the disulphide is 
frozen ; this melts when the glass is placed in the palm of the hand. If a glass plate 
be covered with water, a watch-glass containing carbon disulphide placed on it, and 
evaporation promoted by blowing through a tube, the watch-glass will be frozen on 
to the plate, so that the latter may be lifted up by it. 

The carbon disulphide is exceedingly inflammable ; it takes fire at 
a temperature far below that required to inflame ordinary combustible 
bodies, and burns with a bright blue flame, producing carbonic and 
sulphurous acid gases (CS 2 + 6 = C0 2 + 2S0 2 ), and having a great ten- 
dency to deposit sulphur unless the supply of air is very good. 

The heat of combustion of CS 2 exceeds by 222 centigrade units the sum of the heat 
evolved by the combustion of its constituents in the separate form. 

If a little carbon disulphide be dropped into a small beaker, it may be inflamed 
by holding in its vapour a test-tube containing oil heated to about 300° F., which 
will be found incapable of firing gunpowder or of inflaming any ordinary combustible 
substance. 

The abundance of sulphur separated in the flame of carbon disulphide enables it 
to burn iron by converting it into sulphide. If some carbon disulphide be boiled 
in a test-tube provided with a piece of glass tube from which the vapour may be 
burnt, and a piece of thin iron wire be held in the flame (fig. 212), it will burn with 
vivid scintillation, the fusible ferrous sulphide dropping off. 



PROPERTIES OF BISULPHIDE OF CARBON. 



217 



The vapour of carbon disulphide acts very injuriously if breathed for 
any length of time, producing symptoms somewhat resembling those 
caused by sulphuretted hydrogen. Its poisonous properties have been 
turned to account for killing insects in grain without injuring it. 

The chief applications of carbon disulphide depend upon its power of 
dissolving the oils and fats. After as 
much oil as possible has been extracted 
from seeds and fruits by pressure, a fresh 
quantity is obtained by treating the 
pressed cake with carbon disulphide, 
which is afterwards recovered by distil- 
lation from the oil. In Algiers it is 
employed for extracting the essential oils 
in which reside the perfumes of roses, 
jasmine, lavender, &c. 

Carbon disulphide has often been 
made a starting-point in the attempts to 
produce organic compounds by synthesis. 
It may be employed in the formation of 
the hydrocarbons which are usually de- 
rived from organic sources ; for if it be 
mixed with hydric sulphide (by passing Fig. 212. 

that gas through a bottle containing 

the disulphide gently warmed), and passed over copper-turnings heated 
to redness in a porcelain tube, olehant gas will be produced ; 2CS 2 
+ 2H 2 S'+Cu 6 = 6CuS + C 2 H 4 . 

The action of carbon disulphide upon ammonia is practically import- 
ant for the easy production of ammonium sulphocyanide, which is formed 
when the disulphide is dissolved in alcohol, and acted on by ammonia 
with the aid of heat — 




CS 2 + 

Carbon bisulphide. 



2NH C 



H 2 S + NH 4 CN!S. 

Ammonium sulphocyanide. 



Carbon disulphide is often called sulphocarbonic acid; it combines 
with some of the sulphur-bases to form sulphocarbonates or tMocarbonates, 
which correspond to the carbonates, containing sulphur in place of oxygen. 
Thus, when a solution of potassium sulphide is mixed with an excess of 
carbon disulphide, potassium sulphocarbonate is obtained in orange-yellow 
crystals. Even the hydrogen compound corresponding in composition to 
the unknown H 2 C0 3 may be obtained as a yellow oily liquid by decom- 
posing potassium sulphocarbonate with hydrochloric acid ; K 2 CS 3 + 2HC1 
= H 2 CS S + 2KC1. 

Potassium thiocarbonate is applied for the destruction of the phylloxera 
insect which infests vines. 

As would be expected, the sulphocarbonates, when boiled with water, 
exchange their sulphur for oxygen, becoming carbonates : K 2 CS 3 + 3H 9 
= K 2 C0 3 + 3H 2 S. 

The carbon disulphide vapour in coal gas is one of the most injurious 
of the impurities, and one of the most difficult to remove with economy. 

It is especially injurious, because, when burning in the presence of 
aqueous vapour, a part of its sulphur is converted into sulphuric acid, the 
corrosive effects of which are so damaging. Several processes have been 



218 CARBONIC OXYSULPHIDE. 

devised for its removal. The gas has been washed with the ammoniacal 
liquor (containing ammonium sulphide) which absorbs the disulphide. 
Steam, at a high temperature, has been employed to convert it into 
hydrosulphuric acid and carbon dioxide, which are both easily removed 
from the gas; CS 2 + 2H 2 = C0 2 + 2H 2 S. Lime at a red heat decom- 
poses it in a similar way; CS 2 + 3CaO = CaC0 3 + 2CaS. Oxide of lead 
dissolved in caustic soda has been used to convert it into sulphide of lead ; 
CS 2 4- 2PbO + 2JNaHO = 2PbS + JSTa 2 C0 3 + H 2 0. Its removal as sulpho- 
carbonate by an alcoholic solution of potash or soda has also been pro- 
posed. At present, however, it retains its character as one of the most 
troublesome impurities with which the gas manufacturer has to deal. 

Carbonic oxysulfhide, COS = 60 parts by weight = 2 volumes. This compound, 
which may be regarded as hydrosulphuric acid in which CO has replaced H 2 , is 
formed when a mixture of carbonic oxide with sulphur vapour is acted on by electric 
sparks, or passed through a red hot porcelain tube. 

It is easily prepared by gently heating the potassium sulphocyauide with oil of 
vitriol diluted with four-fifths of its volume of water, and collecting the gas over 
mercury. 

The action of the sulphuric acid upon the sulphocyanide produces hydrosulpho- 
cyanic acid ; KCNS (potassium sulphocyanide) + H 2 S0 4 = HCNS + KHS0 4 ; which is 
then decomposed by the water, in the presence of the excess of sulphuric acid, into 
the carbonic oxysulphide gas and ammonia, which combines with the sulphuric acid, 
HCNS + H 2 = NH 3 + COS. The gas has a peculiar disagreeable odour, recalling 
that of carbon disulphide ; it is more than twice as heavy as air (sp. gr. 2 - ll), and is 
very inflammable, burning with a blue flame, and yielding carbonic and sulphurous 
acid gases. Potash absorbs and decomposes it, yielding carbonate and sulphide of 
potassium ; COS + 4KHO = K 2 S + K 2 C0 3 + 2H 2 . 

153. Silicon disulphide (SiS 2 ), corresponding in composition to carbon disulphide, 
is obtained by burning silicon in sulphur vapour, or by passing vapour of carbon 
disulphide over a mixture of silica and charcoal. Unlike the carbon compound, it is 
a white amorphous solid, absorbing moisture when exposed to air, and soluble in 
water, which gradually decomposes it into silica and hydrosulphuric acid. When 
heated in air it burns slowly, yielding silica and sulphurous acid gas. 

154. Nitrogen sulphide (NS) is a yellow crystalline explosive substance, produced 
when chloride of sulphur, dissolved in carbon disulphide, is acted on by gaseous 
ammonia, 8NH 3 + 3S 2 Cl 2 = 6N"H 4 Cl-t-2NS + S 4 , when ammonium chloride is deposited, 
and the filtered liquid, allowed to evaporate, deposits sulphide of nitrogen mixed with 
sulphur, which may be dissolved out by carbon disulphide, in which the nitrogen 
compound is nearly insoluble ; this substance is remarkable for its sparing solubility, 
its irritating odour, and its explosibility when struck or moderately heated, its elements 
being held together by a very feeble attraction. 

155. Chlorides of sulphur. — The subchloride, or chloride of sulphur, 
or sulphur monochloride (S 2 C1 2 = 135 parts by weight), is the most 
important of these, since it is employed in the process of vulcanising 
caoutchouc. It is very easily prepared by passing dry chlorine over 
sulphur very gently heated in a retort (fig. 213) ; the sulphur quickly 
melts, and the sulphur monochloride distils over into the receiver as a 
yellow volatile liquid (boiling-point, 280° F.), which has a most peculiar 
odour. It fumes strongly in air, the moisture decomposing it, forming 
hydrochloric and sulphurous acids, and causing a deposit of sulphur upon 
the neck of the bottle — 

2S 2 C1 2 + 3H 2 = 4HC1 + H 2 S0 3 + S s . 

When poured into water, it sinks (sp. gr. 1*68) and slowly undergoes 
decomposition ; the separated sulphur, of course, belongs to the electro- 
positive variety (see p. 192), and the solution contains, beside hydro- 
chloric and sulphurous acids, some of the acids containing a larger pro- 



SELENIUM. 



219 



portion of sulphur. If phosphorus dissolved in carbon disulphide be 
mixed with sulphur monochloride, the liquid will take fire on addition of 
ammonia. The specific gravity of the vapour of S 2 C1 2 is 4*7, showing 
that it is 68 times as heavy as hydrogen, giving for its molecular weight 
136, which agrees very nearly with that calculated (135). 




Fig. 213. — Preparation of sulphur monochloride. 

Sulphur dichloride (SC1 2 ) is a far less stable compound than the preceding chloride, 
from which it is obtained" by the action of an excess of chlorine. It is a dark red 
fuming liquid, easily resolved, even by sunlight, into free chlorine and sulphur 
monochloride 

Sutyhur di-iodidc (SI 2 ) is a crystalline unstable substance, produced by the direct 
union of its elements, and occasionally employed in medicine. 

Sulphur moniodide (S 2 I 2 ) is obtained in large tabular crystals, resembling iodine, 
by decomposing the sulphur monochloride with ethyle iodide ; S 2 C1 2 + 2C 2 H 5 I 
= S 2 I 2 + 2C 2 H 5 C1. 

Selenium. 

Se = 79'5 parts by weight. 

156. Selenium (2eA.^i/7j, the moon) is a rare element, very closely allied to sulphur 
in its natural history, physical characters, and chemical relations to other bodies. It 
is found sparingly in the free state associated with some varieties of native sulphur, 
but more commonly in combination with metals, forming selenides, which are found 
together with the sulphides. The iron pyrites of Fahlun, in Sweden, is especially 
remarkable for the presence of selenium, and was the source whence this element was 
first obtained. The Fahlun pyrites is employed for the manufacture of oil of vitriol, 
and in the leaden chambers a reddish-brown deposit is found, which was analysed by 
Berzelius in 1817, and found to contain the new element. 

In order to extract selenium from the seleniferous deposit of the vitriol works, it 
may be boiled with sulphuric acid diluted with an equal volume of water, and 
nitric acid added in small portions until the oxidation is completed, when no more red 
fumes will escape. The solution, containing selenious and selenic acids, is largely 
diluted with water, filtered from the undissolved matters, mixed with about one- 
fourth of its bulk of hydrochloric acid, and somewhat concentrated by evaporation, 
when the hydrochloric acid reduces the selenic to selenious acid — 
H 2 Se0 4 + 2HC1 = H 2 Se0 3 + H 2 + Cl 2 . 

A current of sulphurous acid gas is now passed through the solution, when the 
selenium is precipitated in fine red flakes, which collect into a dense black mass 
when the liquid is gently heated ; H 2 Se0 3 + H. 2 + 2S0. 2 = 2H 2 S0 4 + Se . 

The proportion of selenium in the deposit from the leaden chambers is variable. The 
author has obtained 3 per cent, by this process. 

Selenium, like sulphur, is capable of existing in three allotropic states : the red 
amorphous variety precipitated from its solutions, or sublimed like flowers of sul- 
phur ; the black vitreous form ; and the crystalline form, deposited from its solution 



220 TELLURIUM. 

in carbon disulphide, in which it is far less easily dissolved than sulphur. Vitreous 
selenium, when heated, fuses at a little above 100° (J., boils below a red heat, and 
is converted into a deep yellow vapour, which expands when heated in the same 
anomalous manner as vapour of sulphur. The crystalline selenium has a much 
higher fusing point. 

Selenium is less combustible than sulphur ; when heated in air it burns with a blue 
flame, and emits a peculiar odour like that of putrid horse-radish, which appears to 
be due to the formation of a little selenietted hydrogen from the moisture of the air. 
When heated with oil of vitriol, selenium forms a green solution which deposits the 
selenium again when poured into water. 

Vitreous selenium is a very bad conductor of electricity, but crystalline selenium 
is a fair conductor, and conducts better in light than in darkness, which is taken 
advantage of in the photophone. 

Selenium dioxide (Se0 2 ), corresponding to sulphur dioxide, is the product of com- 
bustion of selenium in oxygen. It is best obtained by dissolving selenium in boiling 
nitric acid (which would convert sulphur into sulphuric acid), and evaporating to 
dryness, when the selenium dioxide remains as a white solid which sublimes in needle- 
like crystals when heated. When dissolved in boiling water, it yields crystalline 
selenious acid, H 2 Se0 3 . 

Selenic acid (H 2 Se0 4 ). — Potassium seleniate is formed when selenium iso xidised by 
fused nitre ; 2KN0 3 + Se = K 2 Se0 4 + 2NO. By dissolving the potassium seleniate in 
water, and adding lead nitrate, a precipitate of lead seleniate (PbSe0 4 ) is obtained, 
and if this be suspended in water and decomposed by passing hydrosulphuric acid 
gas, lead will be removed as insoluble sulphide, and a solution of selenic acid will be 
obtained ; PbSe0 4 + H 2 S = H 2 Se0 4 + PbS. This solution may be evaporated till it has 
a sp. gr. of 2 "6, when it very closely resembles oil of vitriol. It is decomposed, how- 
ever, at about 550° F., evolving oxygen, and becoming selenious acid. It oxidises 
the metals like oil of vitriol, and even dissolves gold. The seleniates closely resemble 
the sulphates, but they are decomposed when heated with hydrochloric acid, chlorine 
being evolved and selenious acid produced. 

Hydroselenic acid, or selenietted hydrogen (H 2 Se), is the exact parallel of sulphuretted 
hydrogen, and is produced by a similar process. It is even more offensive and 
poisonous than that gas, and acts in a similar way upon metallic solutions, precipi- 
tating the selenides. 

There are two chlorides of selenium : the monochloride, Se 2 Cl 2 , a brown volatile 
liquid corresponding to sulphur monochloride ; and the tetrachloride, SeCl 4 , a white 
crystalline solid, without any well-established analogue in the sulphur series. 

Notwithstanding the resemblance between the two elements, there are two sul- 
phides of selenium, a disulphide (SeS 2 ) and a trisulphide (SeS 3 ). The former is 
obtained as a yellow precipitate when hydrosulphuric acid is passed into solution of 
selenious acid. 

Tellurium. 

Te = 129 parts by weight. 

157. Tellurium (from tellus, the earth) is connected with selenium by analogies 
stronger than those which connect that element with sulphur. It is even less fre- 
quently met with than selenium, being found chiefly in certain Transylvanian gold 
ores. It occasionally occurs in an uncombined form, but more frequently in com- 
bination with metals. Foliated or graphic tellurium is a black material containing 
the tellurides of lead, silver, and gold. Bismuth telluride is also found in nature. 
Arsenical pyrites sometimes contains tellurium, apparently as TeS 2 . 

Tellurium is extracted from the foliated ore by a process similar to that for ob- 
taining selenium. From bismuth telluride it is procured by strongly heating the 
ore with a mixture of potassium carbonate and charcoal, when potassium telluride 
is formed, which dissolves in water to a purple-red solution, from which tellurium is 
deposited on exposure to air. 

Tellurium much more nearly resembles the metals than the non-metals in its 
physical properties, and is on that account often classed among the former, but it is 
not capable of forming a true basic oxide. In appearance it is very similar to bismuth 
(with which it is so frequently found), having a pinkish metallic lustre, and being, 
like that metal, crystalline and brittle. It fuses below a red heat, and is converted 
into a yellow vapour at a high temperature. When heated in air it burns with a blue 
flame edged with green, and emits fumes of tellurium dioxide (Te0 2 ) and a peculiar 
odour. 



TELLURIUM. 221 

Like selenium, tellurium is dissolved by strong sulphuric acid, yielding a purple- 
red solution, from which water precipitates it unchanged. 

The oxides of tellurium correspond in composition to those of selenium. Tellurous 
acid (H 2 Te0 3 ) is precipitated when a solution of tellurium in diluted nitric acid is 
poured into water. If the nitric solution is boiled, a crystalline precipitate of 
tellurous anhydride is obtained. Unlike selenious acid, tellurous acid is sparingly 
soluble in water. The anhydride is easily fusible, forming a yellow glass, which 
becomes white on cooling, and may be sublimed unchanged. Tellurous acid is rather 
a weak acid, and with some of the stronger acids the anhydride forms soluble com- 
pounds in which it takes the part of a very feeble base. 

Telluric acid (H 2 Te0 4 ) is also a weak acid obtained by oxidising tellurium with 
nitre, precipitating the potassium tellurate with barium chloride, and decomposing 
the barium tellurate with sulphuric acid. On evaporating the solution, crystals of 
telluric acid (H 2 Te0 4 2H. 2 0) are obtained, which become H 2 Te0 4 at a moderate heat, 
and when heated nearly to redness are converted into an orange-yellow powder, which 
is the anhydride. In this state it is insoluble in acids and alkalies. When strongly 
heated, it evolves oxygen, and becomes tellurous anhydride. The tellurates are 
unstable salts which are converted into tellurites when heated. 

Telluretted hydrogen or hydrotelluric acid (H 2 Te) exhibits in the strongest manner 
the chemical analogy of tellurium with selenium and sulphur. It is a gas very 
similar to sulphuretted hydrogen in smell, and in most of its other properties. 
When its aqueous solution is exposed to the air, it yields a brown deposit of tellurium. 
When passed into metallic solutions it precipitates the tellurides. The gas is pre- 
pared by decomposing telluride of zinc with hydrochloric acid. 

The most characteristic property of tellurium compounds is that of furnishing the 
purple solution of potassium telluride, when fused with potassium carbonate and 
charcoal, and treated with water. Two solid chlorides of tellurium have been obtained; 
TeCl 2 is a black solid with a violet-coloured vapour, and is decomposed by water into 
tellurium and TeCl 4 . The latter may be obtained as a white crystalline volatile solid, 
decomposed by much water, into hydrochloric and tellurous acids. There are also 
two sulphides of tellurium corresponding to the oxides, from which they may be ob- 
tained as dark brown precipitates by the action of hydrosulphuric acid. They are both 
soluble in alkaline sulphides. 

158. Review of the sulphur group of elements. — The three elements — 
sulphur, selenium, and tellurium — exhibit a relation of a similar character 
to that observed between the members of the chlorine group, both in 
their physical and chemical properties. 

Sulphur is a pale yellow solid, easily fusible and volatile, without any 
trace of metallic lustre, and of specific gravity 2*05 (sp. gr. of vapour, 
2 '23). Selenium is either a red powder or a lustrous mass appearing 
black, but transmitting red light through thin layers ; much less fusible 
and volatile than sulphur, and of specific gravity 4*8 (sp. gr. of vapour, 
5*68). Tellurium has a brilliant metallic lustre, is much less fusible and 
volatile than selenium, and of specific gravity 6*65 (sp. gr. of vapour, 9'0). 

Sulphur (atomic weight 32) has the most powerful attraction for oxy- 
gen, hydrogen, and the metals. Selenium (atomic weight 79*5) ranks 
next in the order of chemical energy. Tellurium (atomic weight 129) 
has a less powerful attraction for oxygen, hydrogen, and the metals, than 
either sulphur or selenium. This element appears to stand on neutral 
ground between the non-metallic bodies and the less electro-positive 
metals. 

PHOSPHOKUS. 

P = 31 parts by weight.* 

159. This is -the only element for the ordinary preparation of which 

animal substances are employed. It is never known to occur uncombined 

* The vapour of phosphorus is 62 times as heavy as hydrogen, so that its atom ODly 
occupies half a volume, if the atom of hydrogen be taken to occupy one volume ; and the 
molecule of phosphorus (P 4 ) occupying two volumes would consist of four atoms instead of 
two. 



30-58 


57-67 


2-69 


6-99 


2-07 



222 PHOSPHORUS. 

in nature, but it is found abundantly in the form of phosphate of lime or 
tricalcic diphosphate } 3CaO.P 2 5 or Ca 3 (P0 4 ) 2 , which, is contained in the 
minerals coprolite, phosphorite, and apatite, and occurs diffused, though 
generally in small proportion, through all soils upon which plants will 
grow, for this substance is an essential constituent of the food of most 
plants, and especially of the cereal plants which form so large a propor- 
tion of the food of animals. The seeds of such plants are especially rich 
in the phosphates of calcium and magnesium. 

Animals feeding upon these plants still further accumulate the phos- 
phorus, for it enters, chiefly in the form of calcium phosphate, into the 
composition of almost every solid and liquid in the animal body, and is 
especially abundant in the bones, which contain about three-fifths of 
their weight of calcium phosphate. It is from this source that our 
supply of phosphorus is chiefly derived. 

* Composition of the Bones of Oxen. 

Animal matter, . 
Calcium phosphate, 

,, fluoride, 

,, carbonate, 
Magnesium phosphate, 

100-00 

What is here termed animal matter is a cartilaginous substance, con- 
verted into gelatin when the bones are heated with water under pressure, 
and containing carbon, hydrogen, nitrogen, and oxygen. It was formerly 
the custom to get rid of this by burning the bones in an open fire, but 
the increased demand for chemical products, and the diminished supply 
of bones, have taught economy, so that the cartilaginous matter is now 
dissolved out by heating the bones with water at a high pressure for the 
manufacture of glue ; or the bones are subjected to destructive distilla- 
tion, so as to save the ammonia which they evolve, and the bone charcoal 
thus produced is used by the sugar-refiner until its decolorising powers 
are exhausted, when it is heated in contact with air to burn away the 
charcoal, and leave the bone-ash, consisting chiefly of calcium phosphate, 
Ca 3 (P0 4 ) 2 . In order to extract the phosphorus, the bone-ash is heated 
for some time with diluted sulphuric acid, which removes the greater part 
of the calcium in the form of the sparingly soluble sulphate, leaving the 
phosphoric acid in the solution, which is strained from the deposit, eva- 
porated to a syrup, mixed with charcoal, thoroughly dried in an iron pot, 
and distilled in an earthen retort (fig. 214), when the carbon removes the 
oxygen, and phosphorus distils over, being condensed in a receiver contain- 
ing water to protect it from the action of the air. 

In this process, the sulphuric acid does not remove the whole of the calcium from 
the phosphate, a portion remaining in the solution containing the phosphoric acid, 
so that this solution is generally said to contain superphosphate of lime, and the 
action of the sulphuric acid is thus represented — 

Bone phosphate, Ca 3 (P0 4 ). 2 + 2H 2 S0 4 = CaH 4 (P0 4 ) 2 superphosphate + 2CaS0 4 . 

When the superphosphate is dried, it becomes converted into calcium metaphosphatc 
Ca(P0 3 ) 2 , and on distilling this with charcoal — 

3Ca(P0 3 ) 2 + C ]0 = Ca 3 (P0 4 ) 2 + 10CO + P 4 . 
On the small scale, for the sake of illustration, phosphorus may be prepared by a 
process which has also been successfully employed for its manufacture in quantity, 



EXTRACTION OF PHOSPHORUS FROM BONES. 



223 



and consists in heating a mixture of bone-ash and charcoal in a stream of hydrochloric 
acid gas ; Ca 3 (P0 4 ) 2 + 6HC1 -f- C 8 = 3CaCl 2 + 8CO + H 6 + P 2 . 




Fig. 214. — Extraction of phosphorus. 

A mixture of equal weights of well-dried charcoal and hone-ash, both in fine 
powder, is introduced into a porcelain tube, and placed in a charcoal furnace (fig. 215). 
One end of the tube is connected with a flask (A), containing fused salt and sulphuric 
acid for evolving hydrochloric acid, and the other is cemented with putty into a 
bent retort neck (B), for conveying the phosphorus into a vessel of water (C). On 
heating the porcelain tube to bright redness, phosphorus distils over in abundance. 
The hydrogen and carbonic oxide inflame as they escape into the air, from their con- 
taining phosphorus vapour. 

When first prepared, the phosphorus is red and opaque, from the pre- 
sence of some suboxide of phosphorus and mechanical impurities ; the 
latter are removed by melt- 
ing the phosphorus under 
warm water, and squeezing 
it through wash-leather. 
The phosphorus is then 
fused under ammonia to 
remove any acid impurity, 
and afterwards under potas- 
sium dichromate acidified 
with sulphuric acid, when 
the chromic acid oxidises 
the suboxide of phosphorus, 
and converts it into phos- 
phoric acid which dissolves. 
The phosphorus is then 
thoroughly washed, melted 
under water, and drawn up 
into glass tubes, where it 
solidifies into the sticks in 
which it is sold. These 
are always preserved under 
water from the action of 
oxygen and in tin cases 
from that of light. 

Pure ordinary phospho- lg ' 

rus is almost colourless and transparent, but when exposed to light, and 
especially to direct sun light, it gradually acquires an opaque red colour, 




224 INFLAMMABILITY OF PHOSPHORUS. 

from its partial conversion into the allotropic variety known as red or 
amorphous pi wsplwrus. By tying bands of black cloth ronnd a stick of 
phosphorus and exposing it, under water, to the action of sunlight, 
alternate zones of red may be produced. 

Even though the phosphorus be screened from light, it will not remain 
unchanged unless the water be kept quite free from air, which irregularly 
corrodes the surface of the phosphorus, rendering it white and opaque. 
This action is accelerated by exposure to light. 

The most remarkable character of ordinary phosphorus is its easy in- 
flammability. It inevitably takes fire in air when heated a little above 
its melting-point (111 0, 5 F.), burning with a brilliant white flame, which 
becomes insupportable when the combustion takes place in oxygen (p. 25), 
and evolving dense white clouds of phosphoric anhydride, When a 
piece of dry phosphorus is exposed to the air, it combines slowly with 
oxygen,*" and its temperature often becomes so much elevated during this 
slow combustion, that it melts and takes fire, especially if the combustion 
be encouraged by the warmth of the hand or by friction. Hence, ordinary 
phosphorus must never be handled or cut in the dry state, but always 
under water, for it causes most painful burns. 

The slow oxidation of phosphorus is attended with that peculiar lumi- 
nous appearance which is termed phosphorescence (<££>?, light, </>epa>, to bear), 
but this glow is not seen in pure oxygen or in air containing a minute 
proportion of defiant gas or oil of turpentine. It will be remembered that 
the slow oxidation of phosphorus is attended with the formation of ozone. 

The characteristic behaviour of phosphorus in air is best observed when the phos- 
phorus is in a finely-divided state. When a fragment of phosphorus is shaken with 

a little carbon disulphide, it is quickly 
dissolved, and if the solution be poured 
upon a piece of filtering paper (fig. 216), 
and allowed to evaporate in a darkened 
room, the very thin film of phosphorus 
which is left will exhibit a glow increasing 
in brilliancy till the phosphorus bursts out 
into spontaneous combustion. 

If phosphorus be dissolved in olive oil, 
at a gentle heat, the solution is strongly 
phosphorescent when shaken in a bottle 
Fig. 216. containing air, or when rubbed upon the 

hands. 
Characters may be written on paper with a stick of phosphorus held in a thickly- 
folded piece of damp paper (having a vessel of water at hand into which to plunge 
the phosphorus if it should take fire). When the paper is held with its back to the 
fire, or to a hot iron, in a darkened room, a twinkling combustion of the finely-divided 
phosphorus will ensue, and the letters will be burnt into the paper. Phosphorus 
which has been partly oxidised is even more easily inflamed than pure phosphorus. 
If a few small pieces of phosphorus be placed in a dry stoppered bottle, gently warmed 
till they melt, and then shaken round the sides of the bottle so as to become partly 
converted into red oxide of phosphorus, it will be found, long after the bottle is cold, 
to be spontaneously inflammable, so that if a wooden match tipped with sulphur be 
rubbed against it, 'the phosphorus which it takes up will ignite when the match is 
brought into the air, kindling the sulphur, which will inflame the wood. This was 
one of the earliest forms in which phosphorus was employed for the purpose of pro- 
curing an instantaneous light. ' If the stopper be greased, the phosphorus may be 
preserved unchanged for a long time. 

In the last experiment, if the wood had not been tipped with sulphur, the 

* The white fumes evolved by phosphorus in moist air are said to consist partly of 
ammonium nitrate, formed by the action of the ozonised oxygen upon the air and aqueous 
vapour. 




PREPARATION OF AMORPHOUS PHOSPHORUS. 



225 




phosphorus would not have kindled it, the flame of phosphorus generally being unable 
to ignite solid combustibles, because it deposits upon them a coating of phosphoric 
anhydride, which protects them from the action of air. Hence, in the manufacture 
of lucifer matches, the wood is first tipped with sulphur, or wax, or paraffin, which 
easily give off combustible vapours to be kindled by the flame of the phosphorus 
composition, and thus to inflame the wood. 

If a small stick of phosphorus be carefully dried with filtering paper, and dropped 
into a cylinder of oxygen, which is afterwards covered with a glass plate, no lumino- 
sity will be observed in a darkened room until the cylinder is placed under the air 
pump receiver, and the air slowly exhausted. When 
the oxygen has thus been rarefied to about one-fifth 
of its former density, the phosphorescence will be 
seen. A similar effect may be produced by covering 
the cylinder of oxygen containing the phosphorus 
(having removed the glass plate) with another 
cylinder, about four times its size (fig. 217), filled 
with carbonic acid gas, which will gradually dilute 
the oxygen and produce phosphorescence! By sus- 
pending — in a bottle of air containing a strongly 
luminous piece of phosphorus — a piece of paper with 
a drop of oil of turpentine upon it, the glow may be 
almost instantaneously destroyed. A small tube of 
defiant gas or coal gas dropped into the bottle will 
also extinguish the luminosity.* Fig. 217. 

Ordinary phosphorus is slowly converted into vapour at common 
temperatures, and emits, in the air, white fumes with a peculiar alliaceous 
smell, which appear phosphorescent in the dark. When heated out of 
contact with air, it boils at 550° F., and is converted into a colourless 
vapour. 

The luminosity of phosphorus vapour is seen to advantage when a piece of phos- 
phorus is boiled with water in a narrow-necked flask; or a test-tube with a cork and 
narrow tube. The steam charged with vapour of phosphorus has all the appearance 
of a blue flame, in a darkened room, but of course combustibles are not inflamed by 
it, since its temperature is not higher than 212° F. Phosphorus may be distilled, 
with perfect safety, in an atmosphere of carbonic acid gas, the neck of the retort 
being allowed to dip under water in the receiver. 

Although ordinary phosphorus is of a decidedly glassy or vitreous 
structure, and not at all crystalline, it may be obtained in dodecahedral 
crystals, by allowing its solution in carbon bisulphide to evaporate in 
an atmosphere of carbonic acid gas. 

The conversion of ordinary phosphorus into the red or amorphous phos- 
phorus is one of the most striking instances of allotropic modification. 
When phosphorus is heated for a considerable length of time to about 
450° F. in vacuo, or in an atmosphere in which it cannot burn, it becomes 
converted into a red infusible mass of amorphous phosphorus. This form 
of phosphorus differs as widely from the vitreous form as graphite differs 
from diamond. It is almost unchangeable in the air, evolves no vapour, 
is not luminous, cannot be inflamed by friction, or even by any heat short 
of 500° F., when it actually becomes reconverted into ordinary phos- 
phorus, f Amorphous phosphorus is insoluble in the solvents for ordinary 
phosphorus. The two varieties also differ greatly in specific gravity, that 
of the ordinary phosphorus being 1*83, and of the amorphous variety 2*14. 

* Chappuis finds that when phosphorus is suspended in oxygen, the space glows for a 
short time on adding a little ozone. 

t According to Hittorf, the reconversion does not take place till 800° F., the red phos- 
phorus being convertible into vapour below that temperature, without fusion. 

P 



226 



PROPERTIES OF PHOSPHORUS. 




The conversion of vitreous into amorphous phosphorus may he effected by heating 
it in a flask (A, fig. 218) placed in an oil-bath (B), maintained at a temperature 
ranging from 450° to 460° F., the flask being furnished with a bent tube (C) dipping 
into mercury, and with another tube (D) for supplying carbonic acid gas, dried by 
passing over calcium chloride. The flask should be thoroughly filled with carbonic 
^_^^ acid gas before applying heat, and the 

rv\ tube delivering it may then be closed 

with a small clamp (E). After exposure 
to heat for about forty hours, but little 
ordinary phosphorus will remain, and 
this may be removed by allowing the 
mass to remain in contact with carbon 
disulphide for some hours, and subse- 
quently washing it with fresh disul- 
phide till the latter leaves no phos- 
phorus when evaporated. 

On the large scale, the red phos- 
phorus is prepared by heating about 
200 lbs. of vitreous phosphorus to 450° 
F. in an iron boiler. After three or 
four weeks the phosphorus is found 
to be converted into a hard red brittle. 
Jng. zlb. mass, which is ground by millstones 

under water, and separated from the ordinary phosphorus either by carbon disul- 
phide or caustic soda, in which the latter is soluble. The temperature requires 
careful regulation, for if it be allowed to rise to 500°, the red phosphorus quickly 
resumes the vitreous condition, evolving the heat which it had absorbed during its 
conversion, and thus converting much of the phosphorus into vapour. This recon- 
version may be shown by heating a little red phosphorus in a narrow test-tube, 
when drops of vitreous phosphorus condense on the cool part of the tube. The 
colour of different specimens of amorphous phosphorus varies considerably ; that 
prepared on the large scale is usually of a dark purplish colour, but it may be obtained 
of a bright scarlet colour. Bhombohedral crystals of phosphorus, resembling crystals 
of arsenic in form and metallic appearance, have been obtained by fusing phosphorus 
with lead, and dissolving out the latter with diluted nitric acid (sp. gr. 1*1). 

Ordinary phosphorus is very poisonous, whilst amorphous phosphorus 
appears to be harmless. The former is employed, mixed with fatty sub- 
stances, for poisoning rats and beetles. Cases are, unhappily, not very 
rare of children being poisoned by sucking the phosphorus composition 
on lucifer matches. The vapour of phosphorus also produces a very 
injurious effect upon the persons engaged in the manufacture of lucifer 
matches, resulting in the decay of the lower jaw-bone. The evil is much 
mitigated by good ventilation, or by diffusing turpentine vapour through 
the air of the workroom, and attempts have been made to obviate it 
entirely by substituting amorphous phosphorus for the ordinary variety, 
but, as might be expected, the matches thus made are not so sensitive to 
friction as those in which the vitreous phosphorus is used. 

The difference between the two varieties of phosphorus, in respect to 
chemical energy, is seen when they are placed in contact with a little 
iodine on a plate, when the ordinary phosphorus undergoes combustion 
and the red phosphorus remains unaltered. 

Ordinary phosphorus is capable of direct union with oxygen, chlorine, 
bromine, iodine, sulphur, and most of the metals, with which it forms 
phosphides or phosphurets. ' Even gold and platinum unite with this 
element when heated, so that crucibles of these metals are liable to cor- 
rosion when heated in contact with a phosphate in the presence of a 
reducing agent, such as carbon. Thus the inside of a platinum dish or 
crucible is roughened when vegetable or animal substances containing 



MANUFACTURE OF LUCIFEPc MATCHES. 227 

phosphates are incinerated in it. The presence of small quantities of 
phosphorus in metallic iron or copper produces considerable effect upon 
their physical qualities. 

Phosphorus has the property, a very remarkable one in a non-metal, of 
precipitating some metals from their solutions in the metallic state. If a 
stick of phosphorus be placed in a solution of sulphate of copper, it 
becomes coated with metallic copper, the phosphorus appropriating the 
oxygen. This has been turned to advantage in copying very delicate 
objects by the electrotype process, for by exposing them to the action of a 
solution of phosphorus in ether or carbon disulphide, and afterwards to 
that of a solution of copper, they acquire the requisite conducting metallic 
film, even on their finest filaments. Solutions of silver and gold are 
reduced in a similar manner by phosphorus. 

By floating very minute scales of ordinary phosphorus upon a dilute solution of 
chloride of gold, the metal will be reduced in the form of an extremely thin film, 
which may be raised upon a glass plate, and will be found to have various shades 
of green and violet by transmitted light, dependent upon its thickness, whilst its 
thickest part exhibits the ordinary colour of the metal to reflected light. By heat- 
ing the films on the plate, various shades of amethyst and ruby are developed. If a 
very dilute solution of chloride of gold in distilled water be placed in a perfectly 
clean bottle, and a few drops of ether, in which phosphorus has been dissolved, 
poured into it, a beautiful ruby-coloured, liquid is obtained, the colour of which is 
due to metallic gold in an extremely finely-divided state, and on allowing it to stand 
for some months, the metal subsides as a purple powder, leaving the liquid colourless. 
If any saline impurity be present in the gold solution, the colour of the reduced gold 
will be amethyst or blue. These experiments (Faraday) illustrate very strikingly the 
use of gold for imparting ruby and purple tints to glass and the glaze of porcelain. 

160. Lucifer matches are made by tipping the wood with sulphur, or 
wax, or paraffin, to convey the flame, and afterwards with the match 
composition, which is generally composed of saltpetre or potassium chlorate, 
phosphorus, red lead, and glue, and depends for its action on the easy 
inflammation, by friction, of phosphorus when mixed with oxidising agents 
like saltpetre (KN0 3 ), potassium chlorate (KC10 3 ), or red lead (Pb 3 4 ), 
the glue only serving to bind the composition together and attach it to 
the wood. The composition used by different makers varies much in 
the nature and proportions of the ingredients. In this country, potassium 
chlorate is most commonly employed as the oxidising agent, such matches 
usually kindling with a slight detonation ; but the German manufacturers 
prefer either potassium nitrate or lead nitrate, together with lead dioxide 
or red lead, which produce silent matches. 

Sulphide of antimony (which is inflamed by friction with potassium 
chlorate, see p. 165) is also used in those compositions in which a part of 
the phosphorus is employed in the amorphous form, and fine sand or 
powdered glass is very commonly added to increase the susceptibility of 
the mixture to inflammation by friction. 

The match composition is coloured either with ultramarine blue, Prus- 
sian blue, or vermilion. In preparing the composition, the glue and the 
nitre or chlorate are dissolved in hot water, the phosphorus then added 
and carefully stirred in until intimately mixed, the whole being kept at a 
temperature of about 100° F. The flue sand and colouring matter are 
then added, and when the mixture is complete, it is spread out upon a 
stone slab heated by steam, and the sulphured ends of the matches are 
dipped into it. 

The safety matches, which refuse to ignite unless rubbed upon the 



228 COMPOUNDS OF PHOSPHORUS AND OXYGEN. 

bottom of the box, are tipped with a mixture of antimony sulphide, potas- 
sium chlorate, and powdered glass, which is not sufficiently sensitive to be 
ignited by any ordinary friction, but inflames at once when rubbed upon the 
amorphous phosphorus mixed with glass, which coats the rubber beneath the 
box. On this principle some French matches have been made which can 
be ignited only by breaking the match and rubbing the two ends together. 
It would be very desirable to dispense entirely with the use of phos- 
phorus in lucifer matches, not only because of the danger from accident 
and disease in the manufacture, but because a very large quantity of 
phosphate of lime which ought to be employed for agricultural purposes, 
is now devoted to the preparation of phosphorus, of which six tous are 
said to be consumed annually in this country for the manufacture of 
matches. The most successful attempt in this direction appears to be the 
employment of a mixture of potassium chlorate and lead hyposulphite, 
in place of the ordinary phosphorus composition. 

For illustration, very excellent matches may be made upon the small scale in the 
following manner. The slips of wood are dipped in melted sulphur so as to acquire 
a slight coating. Thirt}^ grains of gelatine or isinglass are dissolved in 2 drachms of 
water in a porcelain dish placed upon a steam-bath ; 20 grains of ordinary phosphorus 
are then added., and well mixed in with a piece of stick ; to this mixture are added, 
in succession, 15 grains of red lead and 50 grains of powdered potassium chlorate. 
The sulphured matches are dipped into this paste, and left to dry in the air. 

To make the safety matches ; 10 grains of powdered potassium chlorate and 10 
grains of antimony sulphide are made into a paste with a few drops of a warm 
solution of 20 grains of gelatine in 2 drachms of water, the sulphured matches being 
tipped with this composition. The rubber is prepared with 20 grains of amorphous 
phosphorus, and 10 grains of finely-powdered glass, mixed with the solution of 
gelatine, and painted on paper or cardboard with a brush. 

161. Phosphorus-fuze composition. — To ignite the Armstrong percussion 
shells, a very sensitive detonating composition was employed, which is com- 
posed of amorphous phosphorus, potassium chlorate, shellac, and powdered 
glass, made into a paste with spirit of wine. This was placed in the little 
cap designed for it, and when dry, waterproofed with a little shellac dis- 
solved in spirit. The fuzes were found too sensitive to bear transport. 

Such a composition may be prepared with care in the following manner : — Four 
grains of powdered potassium chlorate are moistened on a plate with 6 drops of spirit 
of wine, 4 grains of powdered amorphous phosphorus are added, and the whole mixed, 
at arm's length, with a bone-knife, avoiding great pressure. The mixture, which 
should still be quite moist, is spread in small portions upon ten or twelve pieces of 
filtering paper, and left in a safe place to dry. If one of these be gently pressed with 
a stick, it explodes with great violence. It is dangerous to press it with the blade of 
a knife, as the latter is commonly broken, and the pieces projected with considerable 
force. A stick dipped in oil of vitriol of course explodes it immediately. If a bullet 
be placed very lightly upon one of the pellets, and the paper tenderly wrapped round 
it, a percussion shell may be extemporised, which explodes with a loud report when 
dropped upon the floor. 

The detonating toys known as amorces fulminantes are made by enclosing this 
composition between two pieces of thin paper. 1000 of them contain half an ounce 
of the composition. 

162. Oxides of Phosphorus. 



Name. 


Formula. 


By Weight. 


Phosphorus. 


Oxygen. 


Suboxide of phosphorus, . . .1 P 4 
Phosphorous anhydride, . . . | P2Q3 
Phosphoric anhydride, . . . j P>.p5 


124 

62 
62 


16 

48 
80 



PREPARATION OF PHOSPHORIC ACID. 229 



Phosphoric Acids and Phosphates. 

163. The phosphates are by far the most important of the compounds 
of phosphorus. They have been already noticed as almost the only forms 
of combination in which that element is met with in nature, and as indis- 
pensable ingredients in the food of plants and animals. No other mineral 
substance can bear comparison with calcium phosphate as a measure of 
the capability of a country to support animal life. Phosphoric acid itself 
is very useful in calico-printing and in some other arts. 

The mineral sources of this acid appear to be phosphorite, coprolite, and 
apatite, all consisting essentially of calcium phosphate Ca 3 (P0 4 ) 2 , but 
associated in each case with calcium fluoride, which is also contained, 
with calcium phosphate, in bones, and would appear to indicate an organic 
origin for these minerals. Phosphorite is an earthy-looking substance, 
forming large deposits in Estremadura. Apatite (from airardoi, to cheat, in 
allusion to mistakes in its early analysis) occurs in prismatic crystals, and 
is met with in the Cornish tin-veins. Both these minerals are largely 
imported from Spain, Norway, and America, for use in this country as a 
manure. 

Coprolites (kottpos, dung, XlOos, a stone, from the idea that they were 
petrified dung) are rounded nodules of calcium phosphate, which are found 
abundantly in this country. 

Large quantities of phosphates of calcium and magnesium are imported 
in the form of guano, the partially decomposed excrement of sea-fowl. 

Bones, however, must be regarded as the chief immediate source whence 
the calcium phosphate for agricultural purposes is derived. 

Phosphoric acid is obtained from bone-ash by decomposing it with 
sulphuric acid, so as to remove as much of the lime as possible in the 
form of sulphate, which is strained off, and the acid liquid neutralised 
with ammonium carbonate, which precipitates any unchanged calcium 
phosphate, and converts the phosphoric acid into ammonium phosphate. 
On evaporating the solution, and heating the ammonium phosphate, 
ammonia and water are expelled, and metaphosphoric acid (HP0 3 ) is left 
in a fused state, solidifying to a glass on cooling. Thus prepared, however, 
it always retains some ammonia, and is contaminated with soda derived 
from the bones. 

The pure acid is prepared by oxidising phosphorus with diluted nitric 
acid (sp. gr. 1*2), and evaporating the solution until the phosphoric acid 
begins to volatilise in white fumes ; 5HN0 3 + P 3 = 3HP0 3 + H 2 + 5NO. 
Some phosphorous acid is formed at an intermediate stage. A transparent 
glass (glacial phosphoric acid) is thus obtained, which eagerly absorbs 
moisture from the air, and becomes liquid. That which is sold in sticks 
contains much sodium metaphosphate. 

The addition of a little bromine greatly facilitates the action of nitric acid upon 
phosphorus, apparently by forming the phosphorus pentabromide, which is then 
decomposed by water ; PBr 5 + 4H. 2 = H 3 P0 4 + 5HBr. The hydrobromic acid being 
then acted on by nitric acid, bromine is set free to act upon a fresh quantity of 
phosphorus; 3HBr + HN0 3 = P>r 3 f 2H 2 + NO. "When iodine is also added, the 
action is still better. 

1 oz. of phosphorus is placed in 6 oz. of water and 5 grs. of iodine are added ; then, 
drop by drop, 30 grs. of bromine. When the action is over, 6 oz. of nitric acid (sp. 
gr. 1-42) are added, and the vessel is placed in cold water. "When the phosphorus 
has dissolved, the solution is evaporated till its temperature rises to about 400° F. in 
order to expel the excess of nitric acid, the bromine, and the iodine. 



230 



PHOSPHORIC ANHYDRIDE. 



Phosphoric anhydride or phosphorus pentoxide (P 2 ^5) ^ s prepared by 
burning phosphorus in dry air. 

When required in considerable quantity, the anhydride is prepared by burning the 
phosphorus in a small porcelain dish (A, fig. 219) attached to a wide glass tube (B) 
for introducing the phosphorus, and suspended in a glass flask with two lateral necks, 
one of which is connected with a tube containing pumice-stone and oil of vitriol for 
drying the air as it enters, whilst the other neck is provided with a wide tube con- 




Fig. 219. 

veying the anhydride into a bottle, connected, at C, with an aspirator, or cistern of 
water, for drawing air through the apparatus. The first piece of phosphorus is kindled 
by passing a hot wire down the wide tube, but afterwards the heat of the dish will 
always ignite the fresh piece as it is dropped in. The wide tube must be closed with 
a cork whilst the phosphorus is burning. 

A small quantity of phosphoric anhydride is more conveniently prepared by burning 
phosphorus under a large bell-jar of air, under which a shallow dish of oil of vitriol 

has been standing for an hour or two to 
dry the air. This dish is carefully removed 
without disturbing the air within the jar, 
and the well-dried phosphorus is introduced 
in a small porcelain crucible standing upon 
a large glass plate. The phosphorus having 
been kindled with a hot wire, the flakes of 
phosphoric anhydride will be seen falling- 
like snow on to the glass plate, where they 
accumulate in a layer- of considerable thick- 
ness. To preserve it, the solid must be 
immediatly scraped up with a bone or plati- 
num knife, and thrown into a thoroughly 
Fig. 220. dry stoppered bottle. 

Phosphoric anhydride may be fused at a very high temperature, and 
even sublimed. Its great feature is its attraction for water ; left exposed 
to the air for a very short time, it deliquesces entirely, becoming converted 
into phosphoric acid. It is often used by chemists as a dehydrating 
agent, and will even remove the water from oil of vitriol. When thrown 
into water, it hisses like a red hot iron, but does not entirely dissolve at 
once, a few flakes of metaphosphoric acid remaining suspended in the 
liquid for some time. 




PYROPHOSPHORIC AND ORTHO-PHOSPHORIC ACIDS. 23 

The solution obtained by dissolving phosphoric anhydride in water, 
contains monoliy titrated phosphoric acid or metaphosphoric acid (H 2 O.P 2 5 
or HP0 3 ). If a little silver nitrate be added to a portion of it, a trans- 
parent gelatinous precipitate is formed, which is the silver metaphos- 
phate ( AgX0 3 + HP0 8 = HN0 3 + AgP0 3 )." 

If the solution of metaphosphoric acid be heated in a flask for a short 
time, it will lose the property of yielding a precipitate with silver nitrate, 
unless one or two drops of ammonia be added to neutralise it, when an 
opaque white precipitate of silver pyrophosphate (2Ag 2 O.P 2 5 or Ag 4 P 2 O r ) 
is obtained, for the phosphoric acid has now been converted into the 
dihydrated or pyrophosphoric acid (2H 2 O.P 2 5 or H 4 P 2 O r ). The formation 
of the precipitate is thus expressed — 

H 4 P 2 7 + 4AgN0 3 + 4NH 3 = Ag 4 P 2 7 + 4NH 4 N0 3 . 

When the solution of pyrophosphoric acid is mixed with more water 
and boiled for a long time, it gives, when tested with silver nitrate and a 
little ammonia, a yellow precipitate of silver orthophosphate (3Ag 2 O.P 2 5 
or Ag 3 P0 4 ) ; the phosphoric acid having become converted into trihydrated 
phosphoric acid or orthophosphoric acid (3H 2 O.P 2 5 or H 3 P0 4 ), and acting 
upon the silver nitrate in the presence of ammonia, thus — 

H 3 P0 4 + 3AgN0 3 + 3^H 3 = Ag 3 P0 4 + 3NH 4 N0 8 . 

The pyrophosphoric acid (H 4 P 2 7 ) cannot be obtained by the above 
process without an admixture of one of the other acids, but it has been 
obtained in crystals by decomposing the lead pyrophosphate (Pb 2 P 2 7 ) 
with hydrosulphuric acid, and evaporating the filtered solution in vacuo 
over oil of vitriol. 

Trihydrated phosphoric acid may also be obtained in prismatic crystals, 
by evaporating its solution in a similar way. This acid is also called 
orthophosphoric acid (opObs, true), and common phosphoric acid, in 
allusion to the circumstance that the phosphates commonly met with and 
employed in the arts are the salts of this acid. 

It will be perceived, from their formulae, that metaphosphoric, HP0 3 , orthophos- 
phoric, H 3 P0 4 , and pyrophosphoric acid, H 4 P 2 7 , are respectively monobasic, 
tribasic, and tetrabasic acids. The normal sodium salts of these acids are, respec- 
tively, metaphosphate, NaP0 3 , orthophosphate, Na 3 P0 4 , and pyrophosphate, 
Ra 4 P 2 7 . The hydrogen in orthophosphoric and pyrophos- 
phoric acids may be only partly replaced by a metal ; thus 
there are two other orthophosphat.es of sodium, viz., hydro- 
disodic phosphate HNa 2 P0 4 , and dihydrosodic phosphate 
H 2 A T aP0 4 . 

The phosphates commonly met with are all derived from 
orthophosphoric acid; for example, bone-ash, or tricalcic 
orthophosphate, Ca 3 (P0 4 ) 2 ; superphosphate, or monocalcic 
orthophosphate, CaH 4 (P0 4 )2 ; common phosphate of soda, 
or hydrodisodic orthophosphate, HNa 2 P0 4 ; microcosmic salt, 
or hydro-ammonio-sodic orthophosphate HNH 4 lSra(P0 4 ). 

Pyrophosphates and metaphosphates may be obtained by 
the action of heat on the hydro-orthophosphates. 

Thus, if a crystal of the common rhombic sodium phosphate 
(HNa 2 P0 4 .12Aq.) be heated gently in a crucible (fig. 221), 
it melts in its water of crystallisation, and gradually dries Fig. 221. 

up to a white mass, the composition of which, if not heated 

beyond 300° F., will be Na 2 HP0 4 . If a little of this, white mass be dissolved in 
water, the solution will be alkaline to red litmus paper ; and if silver nitrate (itself 
neutral to test-papers) be added to it, a yellow precipitate of silver orthophosphate 
will be obtained, and the solution will become strongly" acid — 

Na 2 HP0 4 + 3AgN0 3 = Ag 3 P0 4 + 2NaN0 3 + HNO s . 




232 HYPOPHOSPHOROUS ACID. 

If the dried sodium phosphate be now strongly heated over a lamp, it will lose 
water, and become pyrophosphate (irvp, fire) 2Na 2 HP0 4 = H 2 + Na 4 P 2 7 . On dis- 
solving this in water, the solution will be alkaline, and will give with silver nitrate a 
white precipitate and a neutral solution ; Na 4 P 2 7 + 4AgN0 3 = Ag 4 P 2 7 + 4NaN0 3 . 

Microcosmic salt (NaNH 4 HP0 4 .4Aq.), when dissolved in water, yields an alkaline 
solution which gives a yellow precipitate with silver nitrate, the liquid becoming 
acid — 

NaNH 4 HP0 4 + 3AgN0 3 = Ag 3 P0 4 + NaN0 3 + NH 4 N0 3 + HN0 3 . 

But if the salt be heated in a crucible, it fuses, evolving water and ammonia, 
and leaving a transparent glass of sodium metaphosphate NaiSTH 4 HP0 4 = H 2 
+ NH 3 + NaP0 3 , which may be dissolved by soaking in water, yielding a slightly acid 
solution, which gives a white gelatinous precipitate with nitrate of silver, the liquid 
being neutral ; JSTaP0 3 + AgN0 3 = AgP0 3 + NaN0 3 . 

All the phosphates may be converted into orthophosphates, by fusing them with 
alkaline hydrate or carbonate.* 

164. Phosphorous anhydride (P 2 3 ) is the product of the slow combustion of phos- 
phorus. If a piece of phosphorus be heated in a long glass tube, into which a very 
slow current of dry air is drawn through a very narrow tube, it burns with a pale blue 
flame, and white flakes of phosphorous anhydride are deposited. It is more easily 
converted into vapour than phosphoric acid. It eagerly absorbs moisture from the 
air, and is decomposed when strongly heated in a sealed tube, yielding free phosphorus 
and phosphoric anhydride ; 5P 2 3 = 3P 2 5 + P 4 . 

Phosphorous acid, H 3 P0 3 , is obtained in solution, mixed with phosphoric and 
hypophosphoric acids, when sticks of phosphorus arranged in separate tubes open at 
both ends, and, placed in a funnel over a bottle, are exposed under a bell-jar, open at 
the top, to air saturated with aqueous vapour. To obtain the pure acid, chlorine is 
very slowly passed through phosphorus fused under water, when the phosphorous 
chloride first formed is decomposed by the water into phosphorous and hvdrochloric 
acids; PC1 3 + 3H 2 = H 3 P0 3 + 3HC1. The hydrochloric acid is expelled by a 
moderate heat, when the phosphorous acid is deposited in prismatic crystals. When 
heated, it is decomposed into phosphoric acid and gaseous phosphuretted hydrogen ; 
4H 3 P0 3 = 3H 3 P0 4 + PH 3 . 

Solution of phosphorous acid gradually absorbs oxygen from the air, becoming 
phosphoric acid. This tendency to absorb oxygen causes it to act as a reducing agent 
upon many solutions ; thus it precipitates finely-divided metallic silver from a solution 
of the nitrate, by which its presence may be recognised in the water in which ordinary 
phosphorus has been kept. The solution of phosphorous acid even reduces sulphurous 
acid, producing sulphuretted hydrogen and sulphur, the latter being formed by the 
action of the sulphuretted hydrogen upon the sulphurous acid; H 2 S0 3 + 3H 3 P0 3 
= 3H 3 P0 4 + H 2 S. 

If solution of phosphorous acid be poured into a hydrogen apparatus, some hydric 
phosphide is formed which imparts a fine green tint to the hydrogen flame. 

HypophospJioric acid, H 4 P 2 6 , is precipitated as a sparingly soluble sodium hypo- 
phosphate, Na 4 P 2 O 6 .10Aq., on adding sodium carbonate to the syrupy liquid produced 
by the oxidation of moist phosphorus in the air. From the sodium salt, a lead-salt 
may be obtained by decomposition with lead acetate, and by treating this with hydro- 
sulphuric acid, an aqueous solution of H 4 P 2 6 is obtained. It is intermediate in pro- 
perties between phosphorous and phosphoric acids, and gives with silver nitrate a 
white precipitate which is not blaekened on boiling. 

165. Hypophosphorous acid (H 3 P0 2 ). — "When phosphorus is boiled with barium 
hydrate and water, the latter is decomposed, its hydrogen combining with part of 
the phosphorus to form hydric phosphide (spontaneously inflammable), which 
escapes, whilst the oxygen of the water unites with another part of the phosphorus, 
forming hypophosphorous acid, which acts on the baryta to form barium hypo- 
phosphite ; this may be obtained by evaporating the solution, in crystals having the 
composition BaH 4 (P0 o ) 9 . The action of phosphorus upon barium hydrate may be 
represented by the equation 3Ba(OH) 2 + 6H 2 + P 8 = 3BaH 4 (P0 2 ) 2 + 2PH 3 . 

Barium hydrate. Barium hypophosphite. 

Some barium orthophosphate is also formed at the same time, as the result of a 
secondary action. ' 

* It has been remarked that the pliancy of the acid character of phosphoric acid par- 
ticularly fits it to take part in the vital phenomena. It may be regarded as three acids 
in one. 



GASEOUS PHOSPHURETTED HYDROGEN. 



233 



By dissolving the barium hypophosphite in water, and decomposing it with the 
requisite quantity of sulphuric acid, so as to precipitate the barium as sulphate, a 
solution is obtained which may be concentrated by careful evaporation. If this 
hypophosphorous acid be heated, it evolves hydric phosphide, and becomes converted 
into phosphoric acid; 2H 3 P0 2 = H 3 P0 4 + PH 3 . -When exposed to the air it absorbs 
oxygen, and becomes converted into phosphorous and phosphoric acids. It is a 
more powerful reducing agent than phosphorous acid. The latter acid does not 
reduce a solution of sulphate of copper, but hypophosphorous acid, when gently warmed 
with it, gives a black precipitate of hydride of copper (CuH), which is decomposed by 
boiling, evolving hydrogen and leaving metallic copper. 

When heated, the hypophosphites evolve hydric phosphide, and are converted 
into phosphates. The sodium hypophosphite (JSTaH 2 P0 2 ) is sometimes used in 
medicine ; its solution has been known to explode with great violence during evapora- 
tion, probably from a sudden disengagement of hydric phosphide. 

The following is a summary of the acids formed by phosphorus with oxygen and 
hydrogen — 



Hypophosphorous acid, 


. . H 3 P0 2 


Hypophosphoric ,, . 


. . H 4 P 2 6 


Phosphorous ,, . 


. . H3PO3 


Metaphosphoric ,, . 


HPO s 


Orthophosphoric ,, . 


H,P0 4 


Pyrophosphoric ,, . 


• • H 4 P 2 7 



166. Suboxide of phosphorus is supposed to constitute the yellow or red residue 
which is left in the dish when phosphorus 
burns in air, but it is always mixed with much 
phosphoric anhydride. If phosphorus be melted 
under water in a flask (fig. 222), and oxygen 
gas be allowed to bubble through it (a brass 
tube being employed to convey the oxygen), 
each bubble of the gas produces a brilliant 
flash, and the phosphorus is converted into 
red flakes, which were believed to be suboxide 
of phosphorus, but are really amorphous phos- 
phorus. The true suboxide of phosphorus (P 4 0) 
appears to be formed when small pieces of phos- 
phorus are covered with phosphorous chloride 
exposed to the air, and afterwards heated with 
water, when the suboxide is deposited as a yellow powder becoming red at high 
temperatures, and inflaming when heated in air. 




Fig. 222. 



Phosphides of Hydrogen. 

167. Although phosphorus and hydrogen do not combine directly, 
there are three compounds of these elements producible by processes of 
substitution, the composition of which is shown in the following table : — 



Name. 


Formula. 


By Weight. 


Phosphorus. 


H ydrogen. 


Gaseous hydric phosphide, 
Liquid hydric phosphide, 
Solid hydric phosphide, . 


PH S 
PH 2 
P 2 H? 


31 
31 

62 


3 
2 

1 



Gaseous hydric phosphide or phosphuretted hydrogen gas, or pliosphine 
(PH 3 = 34 parts by weight = 2 volumes = \ volume P + 3 volumes H), is 
by far the most important of these. It has been mentioned above as 
resulting from the action of heat upon phosphorous acid, and when 
prepared by this process, it is obtained as a colourless gas, with a most 
powerful odour of putrid fish, inflaming on the approach of a light, and 
burning with a brilliant white flame, producing thick clouds of phosphoric 



234 



GASEOUS PHOSPHURETTED HYDROGEN. 




acid. It is slightly heavier than air (sp. gr. 1*19), and has been liquefied 
under high pressure. 

The ordinary method of preparing this gas for experimental purposes consists in 
boiling phosphorus with a strong solution of potash, when water is decomposed, its 
hydrogen combining with one part of the phosphorus, and its oxygen with another 
part forming hypophosphorous acid, which unites with the potash — 

P 4 + 3KHO + 3H 2 = PH 3 + 3KH,P0 2 . 

A few fragments of phosphorus are introduced into a small retort (fig. 223), which 
is then nearly filled with a strong solution of potash (sp. gr. 1*3),* and heated. The 
extremity of the neck of the retort should not be plunged under water until the 

spontaneously inflammable gas is seen 
burning at the orifice, and the retort must 
not be placed close to the face of the 
operator, since explosions sometimes take 
place in preparing the gas, and the boiling 
potash produces dangerous effects. The 
gas may be collected in small jars filled 
with water, taking care that no bubble of 
air is left in them. It contains hydric 
phosphide mixed with free hydrogen, the 
latter being formed from the deoxidation 
of water by the potassium hypophosphite. 
As each bubble of this gas escapes into 
the air through the water of the pneumatic 
trough, it burns with a vivid white flame, 
producing beautiful wreaths of smoke 
(phosphoric anhydride), resembling the 
gunner's rings sometimes seen in firing 
cannon. Small bubbles sometimes escape 
without spontaneously inflaming. If a 
bubble be sent up into a jar of oxygen, 
the flash of light is extremely vivid, and 
the jar must be a strong one to resist the 
concussion. It is advisable to add a trace of chlorine to the oxygen, to insure the 
inflammation of each bubble, for an accumulation of the gas would shatter the jar. 

If this gas be passed through a tube cooled in a freezing mixture of ice and salt, 
the gas escaping from the tube is found to have lost its spontaneous inflammability, 
although it takes fire on contact with flame. The cold tube contains the liquid 
hydric 'phosphide (PH 2 ), which was present in the gas in the state of vapour, and 
caused^ its spontaneous inflammability, for as soon as the liquid comes in contact 
with air it takes fire. When exposed to light, the liquid phosphide is decomposed 
into the gaseous phosphide, and a yellow solid phosphide (P S H), which is not 
spontaneously inflammable ; 5PH 2 = P 2 H + 3PH 3 . It is for this reason that the 
spontaneously inflammable gas loses that property when kept (unless in the dark), 
depositing the solid phosphide upon the sides of the jar. 

By passing a few drops of oil of turpentine up through the water into a jar of the 
spontaneously inflammable gas, this property will be entirely destroyed, whereas 
the addition of a trace of nitrous acid imparts spontaneous inflammability. 

_ Hydric phosphide, when passed through solutions of some of the metals, pre- 
cipitates their phosphides. For example, with sulphate of copper it gives a black 
precipitate of phosphide of copper, 3CuS0 4 + 2PH 3 = 3H 2 S0 4 + P 2 Cu 3 . 

When this black precipitate is heated with solution of potassium cyanide, it evolves 
self-lighting hydric phosphide. + In fact, this is one of the easiest and safest methods 
of preparing this gas ; for the phosphide of copper is readily obtained by simply 
boiling phosphorus in a solution of sulphate of copper. 

Phosphine has great pretensions to rank as the chemical analogue of ammonia, for 
although it has no alkaline properties, it is capable of combining with hydrobromic 
and hydriodic acids to form crystalline compounds analogous to ammonium bromide 
and iodide ; these compounds, however, are decomposed by water. It will be seen 

* 450 grains of common stick potash dissolved in 1000 grains of water. 
+ Cupric cyanide and potassium phosphide being formed, and the latter decomposed 
by water, giving hydric phosphide and potassium hypophosphite. 



Fig. 223. — Preparation of phosphuretted 
hydrogen. 



CHLORIDES OF PHOSPHORUS. 235 

hereafter, that when the hydrogen of phosphine is displaced by certain compound 
radicals, such as ethyle, powerful organic bases are produced. 

The spontaneously inflammable hydric phosphide may also be obtained by throwing 
fragments of calcium phosphide into water ; this substance is prepared by passing 
vapour of phosphorus over red hot quicklime, or simply by heating small lumps of 
quicklime to bright redness in a crucible aDd throwing in fragments of phosphorus, 
closing the crucible immediately. The dark brown mass thus obtained is a mixture 
of pyrophosphate and phosphide of calcium, of somewhat variable composition. 

The calcium phosphide has beeu used in life-buoys for indicating by the flare their 
position on the water. 

When phosphine is decomposed by a succession of electric sparks, 2 volumes of 
the gas yield 3 volumes of hydrogen, the phosphorus being deposited in the red or 
amorphous form. 

168. Two chlorides of phosphorus are known. The trichloride or phosphorous chloride 
(PC1 3 ) is prepared by acting upon phosphorus with perfectly dry chlorine in the appa- 
ratus employed (p. 219) for preparing the chloride of sulphur. Phosphorous chloride 
distils over very easily (boiling-point, 173° '4 F.), as a colourless, pungent liquid 
(sp. gr. 1*62), which fumes strongly in air, its vapour decomposing the moisture of 
the air and producing hydrochloric acid fumes. In contact Avith water the liquid is 
immediately decomposed, yielding hydrochloric and phosphorous acids, as described 
for the preparation of the latter acid (p. 232). Its analogy to phosphorous anhydride 
is shown by its absorbing oxygen when boiled in the presence of that gas, and forming 
the phosphorus oxychloridc (PC1 3 0). It also absorbs chlorine with avidity, becoming 
converted into pentachloride of jrfwsphorus or phosphoric chloride (PC1 5 ). This 
compound, however, is more conveniently prepared by passing chlorine through a 
solution of phosphorus in carbon disulphide, carefully cooled. On evaporation, the 
pentachloride of phosphorus is deposited in white prismatic crystals, which volatilise 
below 212° F., and fume when exposed to air, from the production of hydrochloric 
acid. When thrown into water it is decomposed into phosphoric and hydrochloric 
acids; PC1 5 + 4H 2 = H 3 P0 4 +5F±C1. But if it be allowed to deliquesce in air, only 
a partial decomposition takes place, and the phosphorus oxychloride is formed, 
PC1 5 + H 2 = PCI3O + 2HC1 . 

This oxychloride may also be produced by heating phosphoric chloride with phos- 
phoric anhydride ; P 2 5 + 3PC1 5 = 5PC1 3 0. A more instructive method of preparing 
it consists in distilling the phosphoric chloride with crvstallised boracic acid, 3PC1 5 
+ 3H 2 O.B 2 O 3 = 3PCl 3 + 6HCl + B 2 O 3 . 

Some of the organic acids (succinic, for example) may be obtained in the anhy- 
drous state, as the boracic acid is in this case, by distilling the hydrate with 
phosphoric chloride. The phosphorus oxychloride distils over (boiling-point, 230° 
F.) as a heavy (sp. gr. 17) colourless fuming liquid of pungent odour. Of course, it 
is decomposed by water, yielding hydrochloric and phosphoric acids. It will be 
found of the greatest use in effecting certain transformations in organic substances. 

The analogy between water and hydrosulphuric acid would lead to the expectation 
that a sulphochloride of phosphorus (PC1 3 S), corresponding to the oxychloride, would 
be formed by the action of hydrosulphuric acid upon phosphoric chloride ; PC1 5 + H. 2 S 
= PC1 3 S + 2HC1. It is a colourless faming liquid, which is slowly decomposed by 
water, giving phosphoric, hydrochloric, and hydrosulphuric acids ; PC1 3 S + 4H 2 
=-H 3 P0 4 + 3HCl + H 2 S. When acted on by solution of soda, the sulphochloride of 
phosphorus loses its chlorine to the sodium, and acquires an equivalent quantity of 
oxygen, a sodium sulphoxy '-phosphate (Na 3 P0 3 S.12H 2 0) being deposited in crys- 
tals. This salt evidently corresponds in composition to the sodium orthophosphate 
(£s~a 3 P0 4 .12H 2 0), and its production is expressed by the equation, PC1 3 S + 6XaHO 
= 3NaCl + iSTa 2 P0 3 S + 3H 2 0. Salts of similar composition may be obtained with other 
metallic oxides. 

The bromides and oxybromide of phosphorus correspond to the chlorine compounds. 

Iodine in the solid state combines very energetically with phosphorus, but if the 
two elements be brought together in a state of solution in carbon disulphide, a more 
moderate action ensues, and two iodides of phosphorus may be obtained in crystals ; 
a tri-iodide (PI 3 ) corresponding to the trichloride, and a biniodide (PI 2 ), which has 
no analogue either among the oxygen, chlorine, or bromine compounds of phosphorus. 
PI 5 has also been obtained. 

The addition of a very small quantity of iodine to ordinary phosphorus, fused in a 
flask filled with carbonic acid gas, materially accelerates its conversion into the red 
modification, and allows the change to be effected at a much lower temperature than 



236 THOSPH AMIDES. 

that required when the phosphorus is heated alone, probably because successive 
portions of vitreous phosphorus combine Avith the iodine to form an unstable iodide 
from which the heat separates the phosphorus in the amorphous form. 

169. The sulphides of phosphorus may be formed by the direct combination of 
their elements. If ordinary phosphorus be used, the experiment is not unattended 
with danger, and should be performed under water. It is safer to combine the 
amorphous phosphorus with sulphur, at a moderate heat, in an atmosphere of car- 
bonic acid gas. 

There appear to be at least three sulphides of phosphorus, viz., the subsulphide 
(P 2 S), the sesquisulphide (P 2 S 3 ), representing phosphorous anhydride (P 2 3 ). and the 
pentasulphide (P 2 S 5 )), analogous to phosphoric anhydride (P 2 5 ). 

P 2 S is a yellow oily liquid which may be distilled out of contact with air. 

P 2 S 3 is a yellow solid, easily fusible, and capable of subliming in a crystalline 
form if air be excluded. It may be produced by the action of hydric sulphide upon 
phosphoric chloride ; 2PC1 3 + 3H 2 S = P 2 S 3 + 6HC1 . 

P 2 S 5 crystallises more readily in a fused state than P 2 S 3 . Both these sulphides, 
unlike the P 2 S, are easily decomposed by water. 

170. Phosphamides or amides of phosphoric acid. — When phosphorus oxy chloride 
is acted on by ammonia, ammonium chloride and phosphotriamide are produced; 
the former is dissolved by water, which leaves the phosphotriamide as a white in- 
soluble body, not easily attacked by acids and alkalies ; PC1 3 + 6NH 3 = 3NH 4 C1 
+ N 3 H 6 PO {Phosphotriamide). 

If the sulphochloride, PC1 3 S, be substituted for the oxychloride, the corresponding 
sulphosphotriamide, N 3 H 6 PS, is obtained. 

The action of ammonia on phosphoric chloride yields chlorophosphamide, N 2 H 4 PCL, ; 
PC1 5 + 2NH 3 = 2HC1 + N 2 H 4 PC1 3 . 

When this is boiled with water, a very stable insoluble substance is obtained, 
which is phosphodiamide ; N 2 H 4 PC1 3 + H 2 = 3HC1 + N 2 H 3 PO (phosphodiamide). 

When heated, it evolves ammonia and becomes phosphomonamide ; N 2 H 3 PO = NH 3 
+ NPO. 

The phosphamides may be regarded as being derived from the ammonium ortho- 
phosphates by the abstraction of 3H 2 ; thus — 

(NH 4 ) 3 P0 4 minus 3H 2 = N 3 H 6 PO Phosphotriamide. 
(NH 4 ) 2 HP0 4 ,, ,, = N 2 H 3 PO Phosphodiamide. 
NH 4 H 2 P0 4 „ ,, = NPO Phosphomonamide. 

When boiled with potassium hydrate, the phosphamides acquire the elements of 
water, and are converted into ammonia and potassium orthophosphate. 

AKSENIC. 

As = 75 parts by weight. * 

171. This element is often classed among the metals, because it has a 
metallic lustre and conducts electricity, but it is not capable of forming 
a base with oxygen, and the chemical character and composition of its 
compounds connect it in the closest manner with phosphorus. 

In its mode of occurrence in nature it more nearly resembles the 
sulphur group of elements, for it is occasionally found in the uncombined 
state (native arsenic), but far more abundantly in combination with 
various metals, forming arsenides, which frequently accompany the sul- 
phides of the same metals. The following are some of the chief arsenides 
and arsenio-sidjphides found in the mineral kingdom — 

Kupfernickel, NiAs 

Arsenical nickel, NiAs 2 

Tin -white cobalt, CoAs 2 

Mispickel or arsenical pyrites, FeS 2 .FeAs 2 

Cobalt-glance, CoS 2 .CoAs 2 

Nickel-glance, NiS 2 . NiAs 2 

* The specific gravity of the vapour of arsenic, like that of phosphorus, indicates that 
75 parts by weight only occupy half a volume. Hence the molecule of arsenic must be 
represented by As 4 =2 volumes. 



ARSENIC. 



237 



But arsenic also occurs, like the metals, in combination with sulphur, 
thus we have — 



Red orpiraent or realgar, 
Yellow orpiment, 



As.,S, 



It is from these minerals that arsenic derives its name (apaevcKov, 
orpiment) ; the sulphides of arsenic are also found in combination with 
other sulphides ; thus red silver ore is a compound of the sulphides of 
silver and arsenic (3Ag 2 S.As 2 S 3 ) ; Tennantite contains sulphide of arsenic 
combined with the sulphides of iron and copper • and grey copper ore 
is composed of sulphide of arsenic with the sulphides of copper, silver, 
zinc, iron, and antimony. In an oxidised form arsenic is found in con- 
dicrrite, which contains arsenious anhydride (As 2 ;} ) and cuprous oxide. 
Cobalt-bloom consists of cobalt arseniate or Co 3 (As0 4 ) 2 . 

Arsenical pyrites is one of the principal sources of arsenic and its com- 
pounds, though a considerable quantity is also obtained in the form of 
arsenious anhydride as a secondary product in the working of certain ores, 
especially those of copper, tin, cobalt, and nickel. 

The substance used in the arts under the name of arsenic is really the 
oxide of arsenic or arsenious anhydride (As 2 3 ) ; pure arsenic itself has 
very few useful applications, so that it is not the subject of an extensive 
manufacture. It can be extracted from 
arsenical pyrites (FeS 2 .FeAs 2 ) by heating 
it in earthen cylinders fitted with iron 
receivers, in which the arsenic condenses 
as a metallic-looking crust, the heat ex- 
pelling it from the pyrites in the form of 
vapour. 

On a small scale it may be obtained by heating 
a mixture of white arsenic with half its weight 
of recently calcined charcoal in a crucible (fig. 
224), the mixture being covered with two or three 
inches of charcoal in very small fragments, and 
the crucible so placed that this charcoal may be 
heated to redness first, in order to ensure the 
reduction of any oxide which might escape from 
below. In order to collect the arsenic, another 
crucible, having a small hole drilled through the bottom for the escape of gas, is 
cemented on to the first, in an inverted position, with fire-clay, and protected from 
the fire by an iron plate with 
a hole in it for the crucible. 
The reduction of arsenious 
anhydride by charcoal is thus 
represented — 

As 2 3 + C 3 = As 2 + SCO . 

For the sake of illustration, 
a small quantity of arsenic 
may be prepared from white 
arsenic by a method commonly 
employed in testing for that 
substance. A small tube of 
German glass is drawn out to 
a narrow point (A, fig. 225), 
and sealed with the aid of the blowpipe. 

introduced into the point of the tube, and a few fragments of charcoal are placed in 
the tube itself at B. The charcoal is heated to redness with a blowpipe flame, and 
the point is then heated so as to drive the white arsenic in vapour over the red hot 




Fig. 224. — Extraction of arsenic. 




Fig. 225.— Reduction of arsenious oxide. 

A very minute quantity of white arsenic is 



238 



PROPERTIES OF ARSENIC. 



charcoal, when a shining black ring of arsenic (C) will be deposited upon the cooler 
portion of the tube. 

The arsenic thus obtained is a brittle mass of a dark steel-grey colour 
and brilliant metallic lustre (sp. gr. 5*7). It does not fuse when heated, 
unless in a sealed tube, since it is converted into vapour at 356° F. It is 
not changed by exposure to air, unless powdered and moistened, when 
it is slowly converted into As 2 3 . When heated in air, it oxidises 
rapidly at about 160° F., giving off white fumes of arsenious anhydride 
and a characteristic garlic odour (recalling that of phosphorus), which, is 
also produced when arsenical pyrites is struck with a hammer or pick. 
At a red heat it burns in air with a bluish white flame, and in oxygen 
with great brilliancy. It is not dissolved by water or any simple solvent 
(herein resembling the metals), but is oxidised and dissolved by nitric 
acid. 

In its chemical relations to other elements, arsenic much resembles 
phosphorus, undergoing spontaneous combustion in chlorine, and easily 
combining with sulphur. Like phosphorus also, it combines with many 
metals, even with platinum, to form arsenides, and its presence often 
affects materially the properties of the useful metals. There are some 
reasons for believing in the existence of two allotropic forms of arsenic, 
differing in chemical activity like those of phosphorus. 

Pure arsenic does not produce symptoms of poisoning till a consider- 
able period after its administration, being probably first oxidised in the 
stomach and intestines, and converted into arsenious acid. 



Oxides of Arsenic. 

172. Arsenic forms two compounds with oxygen, corresponding to 
phosphorous and phosphoric anhydrides. 





Formula. 


By Weight. 


Arsenic. 


Oxygen. 


Arsenious anhydride, . 
Arsenic anhydride, . 


As 2 3 

As 2 5 


150 
150 


48 
80 



Arsenious anhydride (As 2 3 =198 parts by weight = 1 volume 
= 1 volume As + 3 volumes 0).* — Unlike phosphorus, arsenic, when 
burning in air, only combines with three atoms of oxygen. Arsenious 
anhydride, or ichite arsenic, is a very useful substance in many branches 
of industry. It is employed in the manufacture of glass, of several 
colouring-matters, and of shot. A large quantity is also consumed for 
the preparation of arsenic acid and arseniate of soda ; it is, indeed, the 
source from which nearly all the compounds of arsenic are procured. 
Small quantities of crystalline arsenious anhydride are occasionally found 
associated with the ores of nickel and cobalt. 

White arsenic is manufactured by roasting the arsenical pyrites, chiefly 
obtained from the mines of Silesia, in muffles or ovens, through which 
air is allowed to pass, when the arsenic is converted into As 2 3 , and the 
sulphur into S0 2 , which are conducted into large chambers in which the 
As 2 3 is deposited as a very fine powder. The iron of the pyrites is 

* The specific gravity of the vapour of arsenious anhydride is 198 times that of hydrogen, 
instead of 99 times according to the usual law. 



ARSENIOUS ANHYDRIDE. 239 

left partly as oxide, and partly as sulphate of iron. The removal of the 
As 2 3 from the condensing chambers is a very unwholesome operation, 
owing to its dusty and very poisonous character. The workmen are 
cased in leather, and protect their mouths and noses with damp cloths, so 
as to avoid inhaling the fine powder. 

This rough white arsenic is subjected to a second sublimation on a 
smaller scale in iron vessels, when it is obtained in the form of a semi- 
transparent glassy mass known as vitreous arsenioiis acid, which gradually 
becomes opaque when kept, and ultimately resembles porcelain. The 
white arsenic sold in the shops is a fine powder, dangerously resembling 
flour in appearance, but so much heavier (sp. gr. 3 "7) that it ought not 
to be mistaken for it. When examined under the microscope, it appears 
in the form of irregular glassy fragments, mixed with octahedral crystals. 
White arsenic softens when gently heated, but does not fuse (unless in a 
sealed tube), being converted into vapour at 380° F., and depositing in 
brilliant octahedral crystals upon a cool surface. The experiment may be 
made in a small tube sealed at one end, the upper part of which should 
be slightly warmed before heating the arsenious anhydride, so as to 
prevent too rapid condensation, which is unfavourable to the formation 
of distinct crystals.* The octahedra are best examined with a binocular 
microscope. This common poison may fortunately be still more easily 
recognised by sprinkling it upon a red hot coal, when a strong odour 
of garlic is perceptible, due to the reduction of the As 2 3 by the heated 
carbon; the vapour of white arsenic itself is inodorous. The sparing 
solubility of white arsenic in water is very unfavourable to its action as 
a poison, for, when thrown into ordinary liquids, it is dissolved in very 
small quantity, the greater part of it collecting at the bottom. Even 
when taken into the stomach in a solid state, its want of solubility 
delays its operation sufficiently to give a better chance of antidotal 
treatment than in the case of most other common poisons. Its compara- 
tive insolubility is shown by its being almost tasteless. 

When thrown into water, arsenious anhydride exhibits great repulsion 
for the particles of that liquid, and collects in a characteristic manner 
round little bubbles of air, forming small white globes which are not 
wetted by the water. Even if stirred with the water, and allowed to 
remain in contact with it for some hours, a pint of water (20 oz.) would 
not take up more than 20 grs. The smallest dose which has been 
known to prove fatal is 2 "5 grs. If boiling water be poured upon pow- 
dered white arsenic, and allowed to remain in contact with it till cold, it 
will dissolve about ^J^ of its weight (22 grs. in a pint). 

When powdered white arsenic is boiled with water for two or three 
hours, 100 parts by weight of water may be made to dissolve 11 -5 parts 
of the anhydride, and when the solution is allowed to cool, about 9 parts 
will be deposited in octahedral crystals, leaving 2 - 5 parts dissolved in 100 
of water (219 grs. in a pint). 

This great increase in the solubility of the arsenious anhydride by long- 
boiling with water is usually attributed to the conversion of the opaque 
or crystalline variety, which always composes the powder, into the 
vitreous modification, which is the more soluble in water. Water, heated 

* When arsenious anhydride is fused in a long tube, sealed at both ends, and buried in 
hot sand, the mass, after cooling, is found to contain some prismatic crystals, which are 
also sublimed on those parts of the tube which have been heated above 390° F. 



240 ARSENITES. 

with arsenious anhydride in a sealed tube, may be made to dissolve its 
own weight of it ; as the solution cools, it first deposits prismatic crystals, 
and afterwards the ordinary octahedral form. The solution is very feebly 
acid to blue litmus paper. 

White arsenic dissolves abundantly in hot hydrochloric acid (a part of 
it being converted into arsenious chloride), and as the solution cools, 
part of the anhydride is deposited in large octahedral crystals. It is said 
that if the vitreous form be dissolved in hydrochloric acid, the formation 
of these crystals will be attended by flashes of light, visible in a darkened 
room; but the opaque variety does not exhibit this phenomenon. 

The vitreous arsenious anhydride has a slightly higher specific gravity 
than the opaque form, and fuses rather more easily. The opaque variety 
appears to be identical in its properties with crystallised arsenious anhydride. 

Solutions of the alkalies readily dissolve arsenious anhydride, forming 
alkaline arsenites, the solutions of which are capable of dissolving arsenious 
anhydride more easily than water, and deposit it in crystals on cooling. 
Arsenious anhydride is sometimes deposited in prismatic crystals from 
its solution in potash, and the same form has been found native. On 
adding a small quantity of hydrochloric acid to the solution of the alka- 
line arsenite, a white precipitate of arsenious anhydride is formed. 

White arsenic has the property of preventing the putrefaction of skin 
and similar substances, and is occasionally employed for the preservation 
of objects of natural history, &c. 

Arsenites. — Arsenious acid, properly so called, has not yet been obtained 
in the separate state. The aqueous solution of white arsenic, when neu- 
tralised exactly with ammonia, yields, with silver nitrate, a yellow preci- 
pitate having the composition Ag' 3 As0 3 ; with cupric sulphate, a green 
precipitate having the composition Cu"HAs0 3 ; with zinc sulphate, a 
white precipitate containing Zn" 3 (As0 3 ) 2 , and with magnesium sulphate, 
a white precipitate of Mg"HAs0 3 . It would appear, therefore, that the 
arsenious acid from which these salts are derived is a tribasic acid having 
the formula H 3 As0 3 , corresponding to boracic acid H 3 B0 3 . Arsenious 
acid does not destroy the alkaline reaction of the alkalies, and it does 
not decompose the alkaline carbonates unless heat is applied, proving it 
to be a feeble acid. The ammonium arsenite is very unstable, evolving 
ammonia freely when exposed to the air. When arsenious anhydride 
is dissolved in a hot solution of ammonia, octahedral crystals of it are de- 
posited on cooling, notwithstanding the presence of ammonia in large excess. 

When the carbonates of potassium and sodium are fused with an excess 
of arsenious anhydride, brilliant transparent glasses are obtained which 
are similar in composition to glass of borax (K 2 As 4 7 and Na 2 As 4 7 ). 

If an alkaline arsenite be fused in contact with platinum, the latter is 
easily melted, combining with a small proportion of arsenic to form a 
fusible platinum arsenide, a portion of the arsenite being converted into 
arseniate. The alkaline arseniates are so much more stable than the 
arsenites, that the latter exhibit a great tendency to pass into the former, 
with separation of arsenic. 

The arsenites of potassium and sodium in solution are sometimes 
employed as sheep-dipping compositions ; and an arsenical soap, com- 
posed of potassium arsenite, soap, and camphor, is used by naturalists 
to preserve the skins of animals. Sodium arsenite is also occasionally 
employed for preventing incrustations in steam-boilers, being prepared 




ARSENIC ACID. 241 

for that purpose by dissolving 2 molecules of white arsenic and 1 mole- 
cule of sodium carbonate. 

Scheele's green is an arsenite of copper prepared by dissolving white 
arsenic in a solution of potassium carbonate, and decomposing the arsenite 
of potassium thus produced by adding sulphate of copper, when the 
arsenite of copper is precipitated. This poisonous colour is used to 
impart a bright green tint to paper hangings, and is sometimes injurious 
to the health of the occupants of rooms thus decorated, since the arsenite 
of copper is often easily rubbed off the paper, and diffused through the 
air in the form of a fine dust, a small portion of which is inhaled with 
every breath. 

The presence of the arsenite of copper in a sample of such paper is readily proved 
by soaking it in a little ammonia, which will dissolve the arsenite of copper to a blue 
liquid, the presence of arsenic in which 
may be shown by acidifying it with a 
little pure hydrochloric acid, and boiling 
with one or two strips of pure copper, 
which will become covered with a steel- 
grey coating of arsenide of copper. On 
washing the copper, drying it on filter- 
paper, and heating it in a small tube 
(fig. 226), the arsenic will be converted 
into arsenious anhydride, which will 
deposit in brilliant octahedral crystals 
on the cool part of the tube. It is 
obvious that, to avoid mistakes, the 
ammonia, hydrochloric acid, and copper fig. 226. 

should be examined in precisely the same 

way, without the suspected paper, so as to render it certain that the arsenic is not 
derived from them. 

The effective green colour of the arsenite of copper also leads to its 
employment as a colour for feathers, muslin, &c, where it is very inju- 
rious to the health of the work-people. It has even been ignorantly or 
recklessly used for colouring twelfth-cake ornaments, (fee. 

Emerald-green is a combination of arsenite and acetate of copper 
obtained by mixing hot solutions of equal weights of white arsenic and 
acetate of copper. 

In quantities short of poisonous doses, white arsenic appears to have a 
remarkable effect upon the animal body. Grooms occasionally employ it 
to improve the appearance of horses, and in Styria it seems to be taken 
by men and women for the same purpose, apparently favouring the secre- 
tion of fat. It is said that a continuance of the custom develops a 
craving for this drug, and enables large doses to be taken without imme- 
diate danger, though the ultimate consequences are very serious. 

Solution of potassium arsenite {Folder's solution) has long been used in 
medicine. 

173. Arsenic acid (H 3 As0 4 ). — This acid has acquired great importance 
in the chemical arts during the last few years, having been employed to 
replace the expensive tartaric acid used in calico-printing, and to furnish, 
by its action upon aniline, the magnificent dye known as Magenta. 

Arsenic acid is prepared by oxidising white arsenic with three-fourths 
of its weight of nitric acid of sp. gr. 1 '35, when it dissolves with evolution 
of much heat and abundant red fumes of nitrous anhydride — 

As 2 3 + 2HM) 3 + 2H 2 = N" 2 3 + 2H 3 As0 4 . 

Q 



242 ARSENIETTED HYDROGEN. 

After cooling, the solution deposits very deliquescent prismatic crystals 
containing 2H 3 As0 4 .Aq. When these are heated to 212° F. they melt, and 
the liquid gradually deposits needle-like crystals of arsenic acid, H 3 As0 4 , 
corresponding to orthophosphoric acid. At 300° F. (149° C), 2H 3 As0 4 
lose H 2 0, and at 500° F. (260° C), they lose 3H 2 0, becoming As 2 5 , 
arsenic anhydride, which is decomposed at a red heat into As 2 3 and 2 . 

Arsenic anhydride has very much less attraction for water than the 
phosphoric anhydride to which it corresponds ; it deliquesces slowly in 
air, and dissolves rather reluctantly in water. Neither does it appear 
that its combinations with water differ from each other, like the phosphoric 
acids, in the salts to which they give rise, arsenic acid forming tribasic 
salts only, like common phosphoric acid. The arseniates correspond very 
closely to the orthophosphates, with which they are isomorphous (i.e., 
identical in crystalline form). Thus the three arseniates of sodium are 
similar in composition to the three orthophosphates, their formulas being 
Na 3 As0 4 .12Aq. ; Na 2 H As0 4 . 1 2 Aq. ; and 2(NaH 2 As0 4 )Aq. 

The common arseniate of soda (]S!"a 2 HAs0 4 7Aq.) is largely used by 
calico-printers as a substitute for the dung-baths formerly employed, since, 
like the common phosphate of soda, it possesses the feebly alkaline pro- 
perties required in that particular part of the process. It is manufactured 
by combining arsenious acid with soda, and heating the resulting arsenite 
with sodium nitrate, from which it acquires oxygen, becoming converted 
into sodium arseniate. 

Calcic arseniate, 2CaHAs0 4 .7H 2 0, has been found in crystalline crusts 
at Joachimsthal. 

Arsenic acid is a much more powerful acid than arsenious acid, being 
comparable, in this respect, with phosphoric acid. It appears to be less 
poisonous than arsenious acid. 

174. Arsenietted hydrogen or hydric arsenide (AsH 3 = 78 parts by weight 
= 2 vols. = J vol. As + 3 vols. H). — The only compound of arsenic and 
hydrogen, the existence of which has been satisfactorily established, is that 
which corresponds to ammonia and phosphine. It is prepared by the action 
of sulphuric acid diluted with three parts of water upon the zinc arsenide, 
obtained by heating equal weights of zinc and arsenic in an earthen 
retort ; 2n 3 As 2 + 3H 2 S0 2 = 2AsH 3 + 3ZnS0 4 . The gas is so poisonous in 
its character that its preparation in the pure state is attended with danger. 
It has a sickly alliaceous odour, and may be liquefied at - 40° F. It. is 
inflammable, burning with a peculiar livid flame, producing water and 
fumes of arsenious anhydride ; 2 AsH 3 + 6 = As 2 3 + 3H 2 0. The chief 
interest attaching to this gas depends upon the circum- 
stance that its production allows of the detection of 
very minute quantities of arsenic in cases in poisoning. 

The application of this test, known as Marsh's test, is the 
safest method of preparing arsenietted hydrogen in order to 
study its properties, for it is obtained so largely diluted with 
free hydrogen that it ceases to be so very dangerous. Some 
fragments of granulated zinc are introduced into a half-pint 
bottle (fig. 227), provided with a funnel-tube (A), and a narrow 
tube (B) bent at right angles and drawn out to a jet at the 
Fig. 227. extremity ; this tube should be made of German glass, so that 

it may not fuse easily. The bottle having been about one- 
third filled with water, a little diluted sulphuric acid is poured down the funnel-tube 
so as to cause a moderate evolution of hydrogen, and after about five minutes (to allow 





TERCHLORIDE OF ARSENIC. 243 

the escape of the air) the hydrogen is kindled at the jet. If a few drops of a solution 
obtained by boiling white arsenic with water be now poured down the funnel, 
arsenietted hydrogen will be evolved together with the hydrogen — 

As 2 3 + Zn 6 + 6H 2 S0 4 = 2AsH 3 + 6ZnS0 4 + 3H 2 . 

The hydrogen flame will now acquire the livid hue above referred to, and a white 
smoke of As 2 3 will rise from it. If a piece of glass or porcelain 
be depressed upon the flame (fig. 228), it will acquire a metallic- 
looking coating of arsenic, just as carbon would be deposited 
from an ordinary gas-flame. Arsenietted hydrogen is easily Fig. 228. 

decomposed by heat, so that if the glass tube through which it 

passes be heated with a spirit-lamp (fig. 229) a dark mirror of arsenic will be 
deposited a little in front of the heated part, and the flame of the gas will lose its 
livid hue. These deposits of arsenic are extremely 
thin, so that a very minute quantity of arsenic 
is required to form them, thus rendering the 
test one of extraordinary delicacy. It must be 
remembered, however, that both sulphuric acid 
and zinc are liable to contain arsenic, so that 
erroneous results may be very easily arrived at by 
this test in the hands of any but those specially 
devoted to such investigations. 

Arsenietted hydrogen, like sulphuretted hydro- 
gen, causes dark precipitates in many metallic 
solutions. 

Hydric phosphide, hydric arsenide, and 
ammonia constitute a group of hydrogen 
compounds having certain properties in Fl S- 229 - 

common, which distinguish them from the compounds of hydrogen with 
other elements. 

Two volumes of each of these gases contain three volumes of hydrogen. 

They are all possessed of peculiar odours, that of ammonia being the 
most powerful and that of hydric arsenide the least. 

Ammonia is powerfully alkaline, phosphine exhibits some tendency to 
play an alkaline part, whilst hydric arsenide seems devoid of alkaline 
disposition. 

All these are inflammable, ammonia being the least so of the group ; 
and all are decomposed by heat, ammonia least easily, and hydric arsenide 
most easily. 

They are all producible from their corresponding oxygen compounds, 
viz., N 2 3 , P 2 ^3' anc ^ -^ s 2^3' by ^ ne ac ti° n oi nascent hydrogen (e.g., by 
contact with zinc and diluted sulphuric acid). 

All three are the prototypes of various organic bases which contain 
some compound radical in place of the hydrogen, thus — 

NH 3 is the prototype of triethylamine, JST(C 2 H 5 ) 3 

PH 3 ,, triethylphosphine, P(C 2 H 5 ) 3 

AsH 3 ,, triethylarsine, As(C 2 H 5 ) 3 . 

175. Arsenic trichloride or arsenious chloride. — Only one compound of chlorine 
with arsenic (AsCl 3 ) is well known.* The trichloride may be formed by the direct 
union of its elements, but the simplest laboratory process for procuring it consists 
in heating white arsenic in dry chlorine gas, in a tubulated retort (A, fig. 229), 
extemporised from a Florence flask (see p. 106). The arsenious anhydride soon 
melts, and the trichloride distils over, leaving a melted mass in the flask, which 
forms a brilliantly transparent glass on cooling, the composition of which varies some- 

* Nickles appears to have succeeded in forming the pentachloride by the action of 
hydrochloric acid gas on As 2 5 in presence of ether ; he describes it as very unstable, and 
easily converted into the trichloride. 



244 



REALGAR — 0RP1MENT. 



what with the temperature employed, but appears to be essentially 2 As 2 3 . As 2 5 . 
The same vitreous compound may be obtained by fusing arsenious and arsenic anhy- 
drides together. 



The reaction may be represented by the equation, HAs 2 3 
+ 3(2As 2 3 .As 2 5 ). 
Arsenic trichloride bears 



a 



4AsCl, 




Fig. 230. 



great general resemblance to phosphorus trichloride ; 
it is a heavy (sp. gr. 2 2), pungent, 
fuming liquid, decomposed by the mois- 
ture of the air, its vapours depositing 
a white coating upon the objects in 
its immediate neighbourhood. When 
poured into water it deposits arsenious 
anhydride; 2AsCl 3 + 3H 2 = As 2 3 + 
6HC1 ; but when dissolved in the 
smallest possible quantity of water 
it deposits crystals of the formula 
AsOCi.H 2 0. 

When white arsenic is dissolved in 
hydrochloric acid, ar&enious chloride is 
formed, As 2 3 + 6HC1 = 2 AsCl 3 + 3H 2 0, 
and remains undecomposed by the 
water in the presence of strong hydro- 
chloric acid, but if water be added, 
arsenious anhydride is precipitated. 
When the solution in hydrochloric acid is distilled, the arsenious chloride distils over, 
and this is sometimes a convenient method of separating arsenic from articles of food, 
&c, in testing for that poison. When heated in dry hydrochloric acid gas, white 
arsenic yields a glassy compound, which contains As 2 3 .AsC10 ; 3As 2 3 + 2HC1 
= 2(As. 2 3 .AsC10) + H 2 0. 

In composition by volume, the arsenious chloride resembles phosphorous chloride 
containing h volume of arsenic vapour, and 3 volumes of chlorine condensed into 

2 volumes, the specific gravity of its vapour being 6 '3. 

Arsenious bromide much resembles the chloride in its chemical characters, but is 
a solid crystalline substance, easily fusible. 

176. Arsenic tri-iodide or arsenious iodide (Asl 3 ) is remarkable for not being 
decomposed by water, like the corresponding phosphorus compound. When obtained 
by heating arsenic and iodine together, it sublimes in brick-red flakes, which, if 
prepared on a large scale, hang in long laminae, like sea-weed. It may be dissolved 
in boiling water, and crystallises out unchanged. It may even be prepared by heating 

3 parts of arsenic with 10 of iodine and 100 of water, when the solution deposits red 
crystals of the hydrated tri-iodide, from which the water may be expelled by a 
gentle heat. 

Asl 3 is precipitated as a golden crystalline powder on mixing a hot solution of 
As.,0 3 in HC1 with a strong solution of KI. 

Arsenic di-iodide, Asl 2 , is obtained by heating 1 part of arsenic and 2 parts of 
iodine in a sealed tube to 230° C, and crystallising from CS 2 in an atmosphere of C0 2 . 
It forms red prismatic crystals which become black when treated with water, accord- - 
ing to the equation 3AsI 2 = 2Asl 3 + As . 

The arsenic tri-fluoridc (AsF 3 ) resembles the trichloride, but .is much more volatile. 
It may be obtained by distilling 4 parts of arsenious anhydride with 5 of fluorspar 
and 10 of strong sulphuric acid, in a leaden retort (see p. 182). It does not attack 
glass unless water be present, which decomposes it into arsenious and hydrofluoric 
acids. 

177. Sulphides of arsenic.' — There are three wel] : known sulphides of 
arsenic, having the composition As 2 S 2 , As 2 S 3 , and As 2 S 5 , the two former 
being found in nature. 

Realgar (As 2 S 2 ) is a beautiful mineral, crystallised in orange-red 
prisms ; but the red orpiment used in the arts is generally prepared by 
heating a mixture of white arsenic and sulphur, when sulphurous acid 
gas escapes, and an orange-coloured mass of realgar is left, 2As 2 3 + S 7 
= 2As 2 S 2 + 3S0 2 . 



SULPHIDES OF ARSENIC. 245 

Another process for preparing it consists in distilling arsenical pyrites 
with sulphur or with iron pyrites — ■ 

FeS 2 .FeAs 2 + 2FeS 2 = 4FeS + As 2 S 2 

Arsenical pyrites. Iron pyrites. o U lDhide Realgar. 

The realgar distils over, and condenses to a red transparent solid. 
Realgar burns in air with a blue flame, yielding arsenious and sulphurous 
anhydrides. If it be thrown into melted saltpetre, it burns with a bril- 
liant white flame, being converted into arseniate and sulphate of potassium. 
This brilliant flame renders realgar an important ingredient in Indian fire 
and similar compositions for fire-works and signal lights. A mixture of 
one part of red orpiment with 3*5 parts of sublimed sulphur and 14 parts 
of nitre is used for signal-light composition. 

Realgar is not easily attacked by acids ; nitric acid, however, dissolves it, with the 
aid of heat, forming arsenic acid and sulphuric acid, with separation of part of the 
sulphur in the free state. Alkalies (potash, for example) partly dissolve it, leaving a 
dark brown substance, which appears to contain free arsenic, 3As 2 S 2 = 2As 2 S 3 + As 2 . 

Yellow orpiment, or arsenious sulphide (As 2 S 3 ), is found native in 
yellow prismatic crystals. The paint known as King's yellow is a mixture 
of arsenious sulphide and arsenious anhydride, prepared by subliming 
a mixture of sulphur with white arsenic, S 9 + 2As 2 3 = 2As 2 S 3 + 3S0 2 . 
It is, of course, very poisonous. 

This substance, like realgar, is not much affected by acids, excepting nitric acid ; 
but it dissolves entirely in potash, forming potassium arsenite and sulpharsenite ; 
6KHO + As 2 S 3 = K 3 AsS 3 + K 3 As0 3 + 3H 2 0. Ammonia also dissolves it easily, forming 
a colourless solution which is employed for dyeing yellow, since if a piece of stuff be 
dipped into it and exposed to air, the ammonia will volatilise, leaving the yellow 
orpiment behind. 

The formation of the characteristic yellow sulphide is turned to account in testing 
for arsenic ; if a solution prepared by boiling white arsenic with distilled water be 
mixed with a solution of hydrosulphuric acid, a bright yellow liquid is produced, which 
looks opaque by reflected, but transparent by transmitted light, and may be passed 
through a filter without leaving any solid matter behind. This solution probably 
contains a soluble compound of arsenious sulphide with hydrosulphuric acid (3H 2 S. 
As 2 S 3 ) ; it is, however, very unstable, being decomposed by evaporation, with preci- 
pitation of the sulphide. The addition of a little hydrochloric acid, or of sal- 
ammoniac, and many other neutral salts, will also cause a separation of the sulphide 
from this solution ; even the addition of a hard water will have that effect. If the 
solution of arsenious acid be acidified with hydrochloric acid before adding the 
hydrosulphuric acid, the bright yellow sulphide is precipitated at once, and may be 
distinguished from any other similar precipitate by its ready solubility in solution of 
ammonium carbonate. 

Arsenic sulphide (As 2 S 5 ) possesses far less practical importance than the preceding 
sulphides ; it may be obtained by fusing As 2 S 3 with sulphur, when it forms an orange- 
coloured glass, easily fusible, and capable of being sublimed, without change. When 
hydrosulphuric acid gas is passed through solution of arsenic acid, a white precipitate 
of sulphur is first obtained, the hydrogen reducing the arsenic acid to arsenious 
acid ; H 3 As0 4 + H 2 S = H 3 As0 3 + H 2 6 + S ; and if the passage of the gas be continued, 
the arsenious acid is decomposed, and arsenious sulphide is precipitated ; these 
changes are much accelerated by heat. But if a solution of sodium arseniate be 
saturated with hydrosulphuric acid, it is converted into sodium sulpharseniate. On 
adding hydrochloric acid to this solution, a bright yellow precipitate of arsenic 
sulphide is obtained. 

Cuprous sulpharseniate or Clarite (Cu 3 AsS 4 ), is found in the Black Forest. 



246 REVIEW OF THE NON-METALLIC ELEMENTS. 



GENEEAL EEVIEW OF THE NON-METALLIC ELEMENTS. 

178. At the conclusion of the history of the non-metals, it may be 
well to call attention to the points of resemblance which classify them 
into separate groups or families, most of which are connected, by some 
analogies, with one or more members of the class of metals. 

Hydrogen stands alone among the non-metals, its chemical properties 
and functions being widely different from those of any other non-metal, 
but connecting it very closely with the most highly electro-positive (or 
basylous) metals, such as potassium and sodium. 

Oxygen, Sulphur, Selenium, and Tellurium compose a group, the mem- 
bers of which (in the state of vapour) combine with twice their volume 
of hydrogen to form compounds which (in the state of vapour) occupy 
the same volume as the hydrogen occupied before combination. All these 
hydrogen compounds are capable of playing a feebly acid part, and their 
hydrogen may be displaced by an equivalent weight of a metal to produce 
compounds exhibiting a general agreement in chemical properties. This 
group is connected with the metals through tellurium, not only by its 
physical properties, but by its forming an oxide (Te0 2 ), which occasion- 
ally acts as a weak base. 

Nitrogen, Phosphorus, aud Arsenic are connected together by the gene- 
ral analogy of their hydrogen and oxygen compounds, the two last mem- 
ber of the group being far more closely connected with each other than 
with nitrogen. With the metals they are connected through arsenic, the 
hydrogen compound of which is very similar in properties, and probably 
in composition, to antimonietted hydrogen ; arsenious anhydride (As 2 3 ) 
is also capable of occupying the place of antimonious oxide (Sb 2 3 ) in 
certain salts of that oxide ; and the sulphides of antimony correspond in 
composition, and in some of their properties, to those of arsenic, One 
form of arsenious anhydride (the prismatic) is isomorphous with native 
oxide of antimony, and this oxide may be obtained in octahedra, the 
ordinary form of arsenious anhydride, so that these oxides are isodi- 
morphous. 

These elements are also connected with the oxygen group through 
sulphur, selenium, and tellurium, the relations of which to hydrogen and 
the metals are somewhat similar to those of phosphorus and arsenic. 

Carbon, Boron, and Silicon resemble each other in their allotropic 
forms, their resistance to fusion and volatilisation, and their forming 
feeble acids. To the metals they are allied through' silicon, which re- 
sembles tin in the composition and character of its oxide and chloride. 

This group is connected with the nitrogen group through boron, for 
boracic acid resembles arsenious acid in its relations to bases, and in 
forming vitreous compounds with the alkalies. In certain compounds 
boracic and arsenious anhydrides are interchangeable. 

Chlorine, Bromine, Iodine, and Fluorine are intimately connected by 
numerous analogies, which have been already pointed out (p. 186). Some 
of the properties of iodine, as its relations to oxygen, and the solubility 
of its trichloride in water, connect it slightly with the metals, whilst 
some of the j:>roperties of the fluorides connect this group with the 
oxygen group of non- metallic elements. 



ATOMIC TYPES. 247 

Atomicity — Quantivalenc e. 

On examining the composition by volume of hydrochloric acid, water, 
ammonia, and marsh gas, it is seen that equal volumes of these com- 
pounds, measured in the gaseous state at the same temperature and pres- 
sure, contain respectively 1, 2, 3, and 4 volumes of hydrogen. 

Thus 2 volumes of hydrochloric acid gas contain 1 volume of chlorine and 
1 volume of hydrogen. 
2 volumes of water vapour contain 1 volume of oxygen and 2 

volumes of hydrogen. 
2 volumes of ammonia contain I volume of nitrogen and 3 volumes 

of hydrogen. 
2 volumes of marsh gas contain 1 volume (?) of imaginary carbon 
vapour and 4 volumes of hydrogen. 
In the case of the marsh gas, it has been already explained that the 
volume occupied by a given weight of carbon vapour cannot be ascer- 
tained by experiment, but there are reasons to justify the assumption that 
12 parts by weight of carbon vapour would occupy the same volume as 1 
part by weight of hydrogen. In the other cases, the above statements 
exhibit the direct results of experiments previously described. 

If it be allowed that one atom of each element occupies one volume, 
then hydrochloric acid, water, ammonia, and marsh gas will contain for 
one atom of chlorine, oxygen, nitrogen, and carbon, respectively, 1, 2, 3, 
and 4 atoms of hydrogen, or, taking the symbol for each element to re- 
present one atom — 

Hydrochloric acid = OH = 

Water = OHH 

Ammonia = NHHH = 

Marsh gas = CHHHH = 

Since, on the atomic theory, hydrogen is accepted as the unit of atomic 
weight and volume, it appears reasonable to fix upon it as representing the 
unit of combining power, and to classify the elements according to the 
tendency of their atoms to imitate the combining power of one or more 
atoms of hydrogen. 

By the atomicity or quantivalence of an element is meant the number 
expressing the hydrogen-atoms to which one atom (or volume) of that 
element is usually equivalent. 

Thus, the atomicity of chlorine is = 1, for one volume (or atom) of 
this element not only combines with, and neutralises the properties 
of, one atom (or volume) of hydrogen, but is capable of representing, 
or occupying the place of, one atom of hydrogen in its compounds (see 
page 154). 

The atomicity of oxygen is = 2, since one volume (or atom) of oxygen 
combines with, and neutralises, two atoms (or volumes) of hydrogen in 
water, and is generally capable of occupying the place of two atoms of 
hydrogen in the compounds of that element. 

The atomicity of nitrogen is = 3, for one volume (or atom) of nitrogen 
neutralises the properties of three atoms (or volumes) of hydrogen in 
ammonia, and is often found to occupy the place of three atoms of hydro- 
gen in its compounds. 

The atomicity of carbon is = 4, for one volume (or atom) of imaginary 





Vols. 


Weights. 




H=l 


H=l 


HC1 


= 2 


= 36-5 


H 2 


_ 2 


= 18 


H 3 N 


— *9 


= 17 


H 4 C 


= 2 


= 16 



248 ATOMIC TYPES. 

carbon vapour is combined, in marsh gas, with four atoms (or volumes) of 
hydrogen, and in its compounds with other elements, one atom of carbon 
is usually found representing four atoms of hydrogen. 

Since hydrochloric acid, water, ammonia, and marsh gas are the most 
conspicuous members of large classes of chemical compounds, they are 
often referred to as types, and the elements, chlorine, oxygen, nitrogen, and 
carbon are taken as the representatives of the various classes into which 
the elements are divided according to their atomicities. 

Cblorineis the type of one-atom elements (technically called mon-atomic 
uni-valent, monad elements), the atomic weights of which are chemically 
equivalent to one part by weight of hydrogen. 

Oxygen is the type of two-atom elements (di-atomic, bi-valent, diad 
elements), of which the atomic weights are chemically equivalent to two 
parts by weight of hydrogen. 

Nitrogen is the type of three-atom elements (tri-atomic, tervalent, 
triad elements), of which the atomic weights are chemically equivalent to 
three parts by weight of hydrogen. 

Carbon is the type of four-atom elements (tetratomic, quadrivalent, tetrad. 
elements), of which the atomic weights are chemically equivalent to four 
parts by weight of hydrogen. It is remarkable that the four elements, 
hydrogen, oxygen, nitrogen, and carbon which compose the chief part of 
living matter are, respectively, monatomic, diatomic, triatomic and tetra- 
tomic elements. 

If the non-metals be classified according to their quantivalence, it will 
be found that, with only few exceptions, the classification will coincide 
with that founded upon their chemical analogies in other respects. Thus, 
the members of the oxygen group are all diatomic, or capable of combining 
with two atoms of hydrogen, as shown by the formulas of their hydrogen 
compounds, H 2 0, H 2 S, H 2 Se, H 2 Te. The nitrogen group is generally re- 
presented as triatomic, their hydrogen compounds being NH 3 , PH 3 , and 
AsH 3 . Boron is also a triatomic element, for, in BC1 3 , the boron occupies 
the place of three atoms of hydrogen. 

Carbon and silicon, however, are tetratomic elements, as shown in 
marsh gas, CH 4 , and in silicon tetrachloride, SiCl 4 . 

Chlorine, bromine, iodine, and fluorine are monatomic, their hydrogen 
compounds having the formulas, HC1, HBr, HI, and HF. 

The atomicity or quantivalence of an element is sometimes expressed 
in a formula by a dash, or dashes, placed above and to the right of the 
element ; thus the symbols, CI', 0", W, C"", indicate the respective 
atomicities of those elements. When the atomicity of an element is 
taken into account, it helps to explain the constitution of compounds 
which would otherwise appear quite anomalous. For example, there is a 
compound of the molecular formula, N 3 H 6 P, obtained by the action of 
phosphorous chloride upon ammonia ; recollecting the triatomic character 
of phosphorus, we perceive this compound to represent three molecules 
of ammonia (N 3 H 9 ), in which phosphorus is the substitute for three atoms 
of hydrogen, which is at once expressed if the formula be written, 
N 3 H 6 P'". Again, carbon oxychloride, C0C1. 2 , appears an inexplicable 
association of elements, until the tetratomic character of carbon and 
diatomic character of oxygen are taken into account, as in the formula 
C""0"Cr 2 , w r hen it appears that the diatomic oxygen and the two atoms 
of monatomic chlorine are the substitutes for four atoms of hydrogen in 



CONSTITUTION OF SALTS. 249 

marsh gas, CH 4 , and it might plausibly be given as a reason why the 
apparently indifferent carbonic oxide should combine with chlorine, that 
the atomicity of the carbon is only partly satisfied in carbonic oxide, 
which contains only oxygen equal in value to two atoms of hydrogen, 
the tetratomic carbon requiring the value of two more atoms of hydrogen 
to satisfy it. In carbon dioxide, C""0" 2 , the two atoms of diatomic oxygen 
satisfy the atomicity of the carbon. 

In a similar manner the absorption of carbonic oxide by cuprous 
chloride may be explained; for the atomic formula of that salt is Cu'Cl', 
and hence it is capable of supplying the two absent atoms in C""0". 

Many more examples of the same kind might be gathered from the 
preceding pages, but these will probably be sufficient to mark the im- 
portance of remembering the atomicities of the elements in speculative 
chemistry ; indeed, without this clue it is impossible to find any meaning 
whatever in a very large number of the formula? of organic substances, 
whilst with it, not only their constitution, but in many cases their mode 
of formation, becomes as intelligible as that of the simplest mineral com- 
pounds. 

Structural Formula? — Bonds. — In speculations relating to the atomic 
structure of compounds, it is now usual to represent graphically the 
atomicity of each element ; thus a monatomic element, like hydro- 
gen, is represented as affording one point of attachment, which may 
be indicated by writing the symbol H — ; a diatomic element, like 
oxygen, affords two points of attachment, as shown by writing its 
atomic symbol — — ; accordingly, to form water, the diatomic oxy- 
gen attaches to itself two atoms of hydrogen, as represented by the 
molecular formula H — — H, whereas in hydric peroxide (H 2 2 ) the 
second atom of oxygen is linked by one point of attachment to the first, 
so that the graphic expression for this compound would be H — — — H. 
A triatomic element, such as nitrogen, has three points of attachment. 
IS r =, and thus, in ammonia, attaches to itself three atoms of hydrogen 
JS T =H 3 . The tetratomic element, carbon, affords four points of attach- 
mentzzCzz, and thus marsh gas (CH 4 ) is represented by H 2 .— C— H 2 , and 
carbon dioxide by OzzCzzO. In carbon monoxide, two of the bonds 
belonging to the carbon are represented as latent or closed, thus OzzCzn, 
so that the carbon here plays the part of a diatomic element.* 

CONSTITUTION OF SALTS. 

179. The term salt, like acid and alkali, was, of course, purely em- 
pirical in its origin, being conferred upon every solid substance which 
exhibited any of the prominent characters of sea salt (sal, brine, a-dXos, the 
sea), such as solubility in water and tendency to crystallisation. 

When the great mass of chemical facts accumulated by the alchemists, 
metallurgists, and apothecaries came be to classified, and the distinction 
between acids and bases was recognised, the term salt was extended to all 
those substances, such as muriate of soda, nitrate of potash, carbonate of 
lime, &c, from which a base and an acid could be obtained, without 
regard to their solubility or tendency to crystallise. When the analytical 
powers of the chemist were more fully developed, it was found that 
muriate of soda and a large class of similar salts did not contain an acid 

* For fuller information upon this subject, the student is referred to Frankland's 
Lecture Notes for Chemical Students. 



250 NEUTRAL AND NORMAL SALTS. 

and a base, but that the acid and base were produced and not educed from 
the salts by the chemical operations to which they were subjected. Thus 
muriate of soda, from which muriatic acid had been so easily produced by the 
action of sulphuric acid, was shown to contain only sodium and chlorine. 

This led to a classification of salts into haloid salts (aAs, the sea), or 
those composed like chloride of sodium, of a metal combined with a salt- 
radical or halogen, and oxy-acid salts, or those composed of a metallic 
oxide combined with an oxygen acid. (It will have been remarked that 
the tendency of modern chemistry is to represent this second class of 
salts by formulae which do not admit the existence of the metal as an 
oxide in the salt.) 

Independently of all differences of opinion with respect to the actual 
constitution of salts, the criterion by which the claims of a substance to 
this title can be estimated is this : a salt is a compound which may be 
formed by the action of an acid upon a base, water, which is a very general 
result of such action, being excepted. 

The oxy-acid salts soon came to be divided into neutral and acid salts, 
according to their effect upon vegetable colours and the organ of taste, 
and a class of basic salts was afterwards added, when it was found that a 
neutral soluble salt sometimes became insoluble by combining with an 
additional quantity of base. 

Further investigation has shown that the neutral state of a salt, and its 
neutrality to test-papers, depend less upon the proportions of the acid and 
base which are contained in it, than upon the chemical energy of these 
substances. 

Thus, potash, acting upon one molecule of sulphuric acid, forms a salt 
which is perfectly neutral to taste and to litmus-papers, whilst with one 
molecule of carbonic acid it forms a strongly alkaline salt ; and one mole- 
cule of sulphuric acid acting upon one molecule of oxide of zinc forms a 
salt which is strongly acid to test-papers. 

A salt may, therefore, be neutral in chemical constitution, and acid or 
alkaline in reaction to test-papers, and it has been proposed to employ the 
term normal to designate those salts which are neutral in chemical con- 
stitution, and to restrict the term neutral to those salts which are neither 
acid nor alkaline to test-papers. Thus, potassium sulphate would be both 
a neutral and a normal salt, whilst zinc sulphate and potassium carbonate 
are normal, but not neutral salts. 

The following definitions are repeated here, on account of their im- 
portance : — 

An acid is a compound containing hydrogen, the whole or part of 
which is displaceable by a metal. 

A salt is a compound derived from an acid by the displacement of its 
hydrogen by a metal. 

A monobasic acid contains but one atom of displaceable hydrogen, and 
therefore can only form one series of salts. 

A dibasic acid contains two atoms of displaceable hydrogen, and there- 
fore can form two series of salts (normal and acid salts). 

A tribasic acid contains ■ three atoms of displaceable hydrogen, and 
therefore can form three series of salts (normal salts, and two series of 
acid salts). 

A normal scdt is one in which the whole of the displaceable hydrogen 
has been displaced by a metal. 



CONSTITUTION OF ACIDS AND SALTS. 



251 



An acid salt is one in which only part of the displaceable hydrogen 
has been displaced by a metal. 

A double salt is one in which the displaceable hydrogen has been 
displaced by different metals. 

A basic salt is a combination of a salt with a basic oxide or with a 
hydrate. 

A few examples may be collected here to illustrate these definitions : — 

Monobasic Acids and Salts. 
Nitric acid, . . . . . HN0 3 

Potassium nitrate, .... KN0 3 



Metaphosphoric acid, .... 


HP0 3 


Sodium metaphosphate, 


NaP0 3 


Dibasic Acids and. Salts. 




Sulphuric acid, 


H 2 S0 4 


Normal potassium sulphate, 


K 2 S0 4 


Acid ,, ,, . . 


KHS0 4 


Carbonic acid (hypothetical), 


H 2 C0 3 


Normal potassium carbonate, 


K 2 C0 3 


Acid 


KHC0 3 


Tribasic Acids and Salts. 




Orthophosphoric acid, .... 


H 3 P0 4 


Normal sodium orthophosphate, 


Na 3 P0 4 


Monacid orthophosphate (or common phosphate), 


Na 9 HP0 4 


Diacid orthophosphate, . 


NaH 2 P0 4 


Microcosmic salt, . . • 


Na(NH 4 )HP0 4 


Arsenic acid, ..... 


H 3 As0 4 


Normal sodium arseniate, 


Na 3 As0 4 


Monacid arseniate, .... 


Na 2 HAs0 4 


Diacid arseniate, .... 


NaH 2 As0 4 



To this view of the constitution of acids and salts, it may be objected 
that it presupposes the existence of a hydrogen compound corresponding 
in composition to the normal salt. Thus the carbonates would be derived 
from an imaginary carbonic acid of the formula H 2 C0 3 ; the arsenites 
from an imaginary arsenious acid, H 3 As0 3 , &c. Indeed, out of the 
twenty-one mineral acids which are of practical importance, there are 
seven which must be thus treated in order to accommodate this theory, 
viz., carbonic, nitrous, sulphurous, arsenious, chromic, hypochlorous, and 
chlorous. It must, however, be acknowledged that no theory of the 
constitution of acids and salts has yet been advanced which is thoroughly 
supported on all sides by experimental evidence. 

From what has been stated above, it will have been seen that an 
examination of the acid itself is by no means necessary in order to ascer- 
tain what its basicity is. If only one series of its salts can be discovered, 
it is a monobasic acid. If a normal and an acid salt (or a double salt) 
can be obtained, the acid is dibasic. When, beside the normal salt, there 
are two series of acid salts, the acid is tribasic. 

Water-type theory of the constitution of salts. — Another ingenious 
theory of the constitution of salts is that known as the water-type theory, 



252 WATER-TYPE THEORY OF ACIDS AND SALTS. 

according to which all oxygen acids are fashioned after the type of water, 
by the displacement of its hydrogen by a compound radical, such displace- 
ment being total in the anhydrides, and partial in the acids. Then, a 
monobasic acid is formed upon the type of one molecule of water, by the 
displacement of one atom of hydrogen to form the acid, and of both 
atoms to form the anhydride. Thus, nitric acid (HN0 3 ) would be written 

NQ ( 0, and nitric anhydride (]ST 2 5 ) would become .t^ 2 \ ; and potas- 
sium nitrate (KISTOg) would be *-r^ > ; a glance at these formulae shows 

why a monobasic acid like nitric acid does not form either acid salts or 
double salts, because it contains only one atom of hydrogen, and therefore 
can only form a single salt with each metal by displacement of that 
hydrogen. This view does not ignore the existence of the anhydride, 
and assumes, as the radical of the acid, the substance N0 2 , which has 
the composition of nitric peroxide. The formation of nitric acid by the 
action of water upon nitric anhydride would be thus expressed — 
HI n N0 2 ) n H ) n N0 2 ) n 
h| + m\i ° = NOj ° + H J ' 

In a similar manner, phosphoric anhydride (P 2 5 ) would be represented 

PO ) H ) 

by p^. 2 > 0, metaphosphoric acid (HP0 3 ) by p~ > 0, and the sodium 

metaphosphate by p~ > . In this case, however, the radical P0 2 is, 

so far as we know, imaginary. 

A dibasic acid is one which is composed after the type of a double 

XT \ 

molecule of water, -pr 2 > 2 , and therefore contains two atoms of hydro- 
gen which may be displaced either entirely by a metal, yielding a normal 
salt, or partly by a metal, yielding an acid salt, or by two metals, yield- 
ing a double salt. For example, sulphuric acid (H 2 S0 4 ) would be 

TT \ 

qA " ( ^2' or * wo m olcules of water, in which two atoms of hydrogen 

are displaced by the diatomic radical S0 2 ; normal potassium sulphate 

SO " r ^2' ac ^ potassium sulphate (bisulphate of potash) ~~ „ > 2 , and 

SO " ) 
sulphuric anhydride, L 2 „ > 2 . 

Here the radical S0 2 has the same composition as sulphurous oxide, 

which might well be accepted as the radical of sulphuric acid. 

CO" ) 
Again, carbonic anhydride would be p~„ > 2 , the imaginary carbonic 

acid, pA„ > 2 , potassium carbonate, pA„ > 2 , acid potassium carbonate, 

CO" ( ^2» carbonate of potassium and sodium, p^„ > 2 . 

The radical of carbonic acid, therefore (CO), would have the same com- 
position as carbonic oxide, which is seen to have a diatomic character in 
its compound with chlorine (C0)"C1 2 , where it occupies the place of two 
atoms of hydrogen. 

In applying this view to pyrophosphoric acid (H 4 P 2 7 ), some difficulty 
arises because its formula cannot be written on the type of two molecules 



CONSTITUTION OF POLYBASIC ACIDS. 253 

of water (H 4 2 ) on account of the indivisibility of the 7 into two whole 
numbers ; it is therefore necessary to take four molecules of water as the 
type, when we have — 

TT \ XT \ 

Type, TT 4 > 4 , pyrophosphoric acid, ,p 4 ~ v„„ > 4 , pyrophosphate of 

Na ) • • ]N"a. H I 

sodium, /p 4 n v „, > 4 , acid pyrophosphate of sodium, " p 2 n %„„ V 4 . 

Here the increased complexity of the formulae appears objectionable. 

A few salts are known in which two acids are combined with the same base, such 
as the acetonitrate of barium, composed of nitrate and acetate of barium. It is 
obvious that the same reasoning which leads to the conclusion that an acid capable 
of forming a double salt with two different bases is dibasic, or contains a diatomic 
acid radical, would also support the inference that a base capable of forming a double 
salt with two different acids is di-acid, or contains a diatomic basic radical. Hence 
the existence of the above acetonitrate of barium countenances the belief that barium 
is a diatomic metal. The formula of the salt would then be written, on the tvpe of 

Ba" ) 
two molecules of water, thus — (C 2 H 3 0)' /> 2 . 

(N0 2 )' ) 

A tribasic acid is formed upon the type of a treble molecule of water, 
thus — 

TT j TT "J 

Type, tt 3 > 3 , orthophosphoric acid, r>h>» \ 3 , sodium orthophos- 

phate, -pry" \ O3 ? common phosphate of sodium, -pry" \ 3 , microcos- 

mic salt (phosphate of sodium and ammonium), pry" f O3 • 
But in this case also an unknown radical, PO, is assumed. 

TT \ 

If pyrophosphoric acid be represented by /pV)y"/pr) y 4 , its inter- 

TT ) 
mediate position between metaphosphoric acid p r , , > 0, and orthophos- 

TT \ 

phoric acid pA/// \ 3 is at once apparent. 

Hydroxyle theory of the constitution of acids. — By a simple modification 
of the water-type theory, the acids may be represented as containing the 
group hydroxyle (HO). A monobasic acid would contain one hydroxyle 
group ; thus, nitric acid would be HO.ISr0 2 ; a dibasic acid would contain 
(H0) 2 ; e.g., sulphuric acid (HO) 2 .S0 2 ; and so for other acids. 

The three phosphoric acids would then become — 



Metaphosphoric, 
HP0 3 




op/° 

U± { OH 




( 


0P ( OH 
U± ) OH 


Pyrophosphoric, 
H 4 P 2 7 



0p fOH 






(OH 


Orthophosphoric, . 
H 3 P0 4 


' 


0P<^ OH 

(oh 



CHEMISTRY OF THE METALS, 



180. The general principles of chemistry having been explained and 
illustrated ia the history of the non-metallic elements, the chemistry of 
the metals will be discussed with less attention to details, which, however 
interesting in a strictly chemical sense, are not, at present, of immediate 
practical importance. 

The definition of a metal has been already given at page 29, as an 
element capable of forming a base by union with oxygen. It will also be 
noticed that the metals are but little disposed to form combinations with 
hydrogen; but that they evince very powerful attraction for the chlorine 
group of elements, with which they form, as a rule, compounds which 
dissolve, without apparent decomposition, in water. 

Classification of the Metals. 

The metals may be divided into ten classes or groups. 

I. Potassium group.— The metals of this group are distinguished by 
their property of forming hydrates which are very soluble in water and 
very strongly alkaline. Each metal of this group forms one chloride, 
containing one atom of metal and one atom of chlorine. 

Potassium Group. 



Atomic 
Weight. 
Lithium, . . .7 

Sodium, . . .23 

Potassium, . . .39*1 



Atomic 
Weight. 
Rubidium, . . 85 '3 

Caesium, . . .133 



II. Calcium group. — The metals of this group form hydrates which 
are much less soluble in water than those of the potassium group, but 
which are also strongly alkaline. Each metal of this group forms a 
chloride, containing one atom of the metal and two atoms of chlorine. 

Calcium Group. 

Atomic Weight. 
Calcium, . . . . . .40 

Strontium, . . . . . 87 '5 

Barium, ...... 137 

III. Magnesium group. — The metals of this group also form one 
chloride, containing one atom of metal and two atoms of chlorine ; but 
they form hydrates which are not soluble in water, and are not strongly 
alkaline. 

Magnesium Group. 

Atomic 
Weight. 
.65 
. 112 





Atomic 






Weight. 




Glucinum, . 


. 9'2 


Zinc, . 


Magnesium, . 


. 24-3 


Cadmium, 



CLASSIFICATION OF THE METALS. 



255 



IV. Aluminium group. — The metals of this group form one chloride 
containing one atom of metal and three atoms of chlorine. Each metal 
also forms one oxide, which is a weak base, and contains two atoms of 
the metal and three atoms of oxygen. The metals enclosed in paren- 
theses have been but little studied, and it is doubtful whether their 
chlorides and oxides are composed as above stated, though their general 
characters appear to give them a place in this group. 



Aluminium 

(Yttrium, 

Gallium, 

(Zirconium 

(Erbium, 

V. Iron g? 



Aluminium 


Group. 


Atomic 




Weight. 




. 27-5 


Indium, 


. 617) 


Lanthanium 


69-9) 


Didymium, 


. 89'5) 


(Thorinum, 


. 112-6) 





Atomic 

Weight. 

113-4 

139 

144-8 

231-5) 



"oup. — The metals of this group form two compounds with 
oxygen, one of which contains single atoms of the metal and oxygen, 
and is a pretty strong base ; the other contains two atoms of metal com- 
bined with three atoms of oxygen, and behaves to acids either as a 
weak base or as an indifferent oxide. (Cerium will be found to present an 
exception in the composition of its oxides.) 



Iron, . 

Cobalt, 
Nickel, 



Iron Group, 

Atomic 
Weight. 
. 56 
. 59 
. 59 



Uranium, 
(Cerium, 



Atomic 
Weight. 
120 
138) 



VI. Manganese group. — The metals of this group differ from those of 
the preceding groups by forming well-defined salts in which the metal 
enters into the composition of the acid radical (viz., chromates, man- 
ganates, vanadiates, molybdates). From the groups which follow, this 
group is distinguished by forming at least two chlorides, containing 
metal and chlorine in the atomic ratios of 1 : 2 and 1 : 3 respectively. 



Manganese Group. 



Vanadium, 
Chromium, 



Atomic 

Weight. 

51-3 

52-5 



Manganese, 
Molybdenum, 



Atomic 

Weight. 

55 



VII. Antimony group. — The two members of this group are brittle 
metals, the chlorides of which are easily decomposed by water. 



Antimony Group. 



Antimony, 
Bismuth, . 



Atomic Weight. 
. 120 
. 210 



VIII. Tin group. — Each of the metals of this group forms a compound 
with two atoms of oxygen which is insoluble in acids but dissolves in 
the alkalies, forming salts. 

Tin Group. 



Titanium, 
Niobium, 
Tin, . 



Atomic 
Weight. 
50 
94 
118 



Tantalum, 
Tuugsten, 



Atomic 
Weight. 

182 

184 



256 



PERIODIC LAW OF THE CHEMICAL ELEMENTS. 



IX. Silver group. — The metals of this group are capable of forming an 
insoluble chloride. 



Copper, 

Silver, 

Mercury, 



Silver 


Group. 


Atomic 




Weight. 




63-5 


Thallium, 


108 


Lead, 


200 





Atomic 
Weight. 

204 

207 



X. Platinum group. — The metals of this group form chlorides which 
combine with the chlorides of the metals of Group I. to form easily 
crystallised double salts. 

Platinum Group. 





Atomic 






Weight. 




Rhodium, . 


. 104-3 


Platinum 


Ruthenium, 


. 104-2 


Iridium, 


Palladium, 


. 106'5 


Osmium, 


Gold, 


. 196-6 





Atomic 

Weight. 

197'1 

197-1 

199 



Periodic law of the chemical elements. — This law, as stated by 
Mendelejeff, is to the effect that "the properties of simple bodies, the 
constitution of their combinations, as well as the properties of the latter, 
are periodic functions of the atomic weights of the elements." In other 
words, if the elements be arranged in the order of their atomic weights, 
they approximate to a series with periodically recurring changes in the 
chemical and physical functions of its members. 

By observing the gaps which exist in this series, Mendelejeff endeavours 
to predict the properties of elements which have yet to be discovered, and 
did indeed foretell, with considerable precision, the properties of gallium, 
in anticipation of its discovery. 

The following table Illustrates this periodic law : the elements being 
divided into 7 groups according to the formulae of their oxides or hydrides, 
as given at the head of each column, and into 6 series, the members of 
which exhibit similarity in physical and chemical functions. 



Group 


1 


2 


3 


4 


5 


6 


7 


Series. 


R 2 


RO 


R 2 3 


R0 2 


R 2 3 


RH 2 
R0 3 


RH 
R 2 7 


1 


Li 7 


G 9 


B 11 


C 12 


N 14 


O 16 


F 19 


2 


Na23 


Mg 24 


Al 27 


Si 28 


P 31 


S 32 


CI 35 


3 


K 39 


Ca 40 




Ti 48 


V 51 


Cr 52 


Mn 55 


4 




Zn 65 


Ga 70 




As 75 


Se 78 


Br 80 


5 


Rb 85 


Sr 87 




Zr 90 


Nb 94 


Mo 96 




6 




Cd 112 


In 113 


Sn 118 


Sb 122 




I 127 



The blanks in such a table indicate where new elements 



may 



be 



expected. Thus, the 4th and 6th members of group 1 are as yet unknown, 
and their properties must be similar to those of potassium and rubidium ; 
the third member of group 3, when discovered, will have properties in- 
termediate between those of aluminium and gallium. 

This periodic classification of the elements bears some resemblance to 
the classification of organic compounds in homologous series. 



CARBONATE OF POTASH. 257 



POTASSIUM. 

K' = 39 parts by weight. 

The indispensable alkali, potash, appears to have been originally 
derived from the granitic rocks, where it exists, in combination with 
silica and alumina, in the well-known minerals felspar and mica. 
These rocks having, in course of time, disintegrated to form soils for the 
support of plants, the potash has been converted into a soluble state, and 
has passed into the plants as a necessary portion of their food. 

In the plant the potash is found to have entered into various forms 
of combination ; thus, most plants contain sulphate and chloride of 
potassium ; but the greater portion of the potassium exists in the form of 
salts of certain vegetable acids formed in the plant, and when the latter 
is burnt these salts are decomposed by the heat, leaving the potassium in 
the form of carbonate. 

Carbonate of potash or potassium carbonate, K 2 C0 3 . — When the ashes 
of plants are treated with water, the salts of potassium are dissolved, 
those of calcium and magnesium being left. On separating the aqueous 
solution and evaporating it to a certain point, a great deal of the potassium 
sulphate, being much less soluble, is deposited, and the carbonate remains 
in the solution ; this is evaporated to dryness, when the carbonate is left, 
mixed with much potassium chloride, and some sulphate ; this mixture 
constitutes the substances imported from America and other countries 
where wood is abundant, under the name of potashes, which are much in 
demand for the manufacture of soap and glass. When further purified, 
these are sold under the name of pearlash, but this is still far from being 
pure potassium carbonate. 

During the fermentation of the grape-juice, in the preparation of wine, 
a hard crystalline substance is deposited, which is known in commerce 
by the name of argot, or, when purified, as cream of tartar. The chemical 
name of this salt is bitartrate of potash or hydropotassic tartrate, for it is 
derived from potash and tartaric acid, a vegetable acid having the com- 
position H 2 C 4 H 4 6 . When this salt (KHC 4 H 4 6 ) is heated, it leaves 
potassium carbonate mixed with carbon; but if the heat be continued, 
and free access of air permitted, the carbon will be entirely burnt away, 
and potassium carbonate will be left (salt of tartar). 

In wine-producing countries potassium carbonate is prepared from 
the refuse yeast which rises during the fermentation, and is dried in the 
sun in order to be subsequently incinerated. 

The fleeces of sheep contain a considerable proportion of salt of 
potassium with an animal acid • when the fleece is washed with water 
this salt is dissolved out, and on evaporating the liquid and burning the 
residue it is converted into potassium carbonate. 

Potassium carbonate is also made from potassium sulphate by a process 
similar to that by which sodium sulphate is converted into carbonate 
(182). Potassium chloride is converted into potassium carbonate by 
decomposing it with the carbonate of trimethylamine (see trimethylamine). 

Hydrate of potash or potassium hydrate, T&R.O. — Carbonate of potassium 
was formerly called potash, and was supposed to be an elementary sub- 
stance. It was known that its alkaline qualities were rendered far more 
powerful by treating it with lime, which caused it to be termed mild 

E 



258 CAUSTIC POTASH. 

alkali, in order to distinguish it from the caustic* alkali obtained, by 
means of lime, and possessed of very powerful corrosive properties. Lime, 
it was said, is derived from limestone by the action of fire, and therefore 
owes its peculiar properties to the acquisition of a certain amount of the 
matter of fire, which, in turn, it imparts to the mild alkali, and thus 
confers upon it a caustic or burning power. 

Black's researches in the middlle of the eighteenth century, which are 
often referred to as models of inductive reasoning, exposed the fallacy of 
this explanation, and proved that instead of acquiring anything from the 
fire, the limestone actually lost carbonic acid gas, and instead of imparting 
anything to the mild alkali, the lime really gained as much carbonic acid 
as it previously lost. 

The caustic potash, so largely employed by the soap-maker, is obtained 
by adding slaked lime to a boiling diluted solution of the potassium 
carbonate, when calcium carbonate is deposited at the bottom of the 
vessel, whilst hydrate of potash remains in the clear solution — 

K 2 C0 3 + Ca(HO) 2 = CaC0 3 + 2KHO 

Potassium Calcium Calcium Potassium 

carbonate. hydrate. carbonate. hydrate. 

If the solution be too strong the lime will not decompose the carbonate. 

When the solution is evaporated, the potassium hydrate remains as a 
clear oily liquid, which solidifies to a white mass as it cools, and forms 
the fused potash of commerce, which is often cast into cylindrical sticks 
for more convenient use.t The potassium hydrate is the most powerful 
alkaline substance in ordinary use, and is very frequently employed by r 
the chemist on account of its energetic action on the different acids. It 
is generally used in the state of solution, the strength of which is inferred 
from its specific gravity, this being higher in proportion to the amount of 
potash contained in the solution. 

Potassium.— -Of the composition of potassium hydrate nothing was 
known till the year 1807, when Davy succeeded in decomposing it by 
the galvanic battery ; this experiment, which deserves particular notice, 
as being the first of a series resulting in the discovery of so many 
important metals, was made in the following manner : — A fragment of 
potassium hydrate, which, in its dry state, does not conduct electricity, was 
allowed to become slightly moist by exposure to the air, and placed upon 
a plate of platinum attached to the copper end of a very powerful galvanic 
battery ; when the wire connected with the zinc end was made to touch 
the surface of the hydrate, some small metallic globules resembling 
mercury made their appearance at the extremity of this (negative) wire, 
at which the hydrogen contained in the hydrate was also eliminated, 
whilst bubbles of oxygen were separated on the surface of the platinum 
plate connected with the positive wire (see p. 9). By allowing the 
negative wire to dip into a little mercury contained in a cavity upon 
the surface of the potash, a combination of potassium with mercury 
was obtained, and the mercury was afterwards separated by distillation. 
This process, however, furnished the metal in very small quantities, and, 
though it w r as obtained with greater facility a year or two afterwards by 
decomposing potassium hydrate with white hot iron, some years elapsed 

* From KaLU), to burn. 

+ These have sometimes a greenish colour, due to the presence of some potassium 
manganate. 



POTASSIUM. 



259 



before any considerable quantity of potassium was prepared by the present 
method of distilling in an iron retort an intimate mixture of potassium 
carbonate and carbon, obtained by calcining cream of tartar • in this 
process the oxygen of the 
carbonate is removed by 
the carbon in the form of 
carbonic oxide (K 2 C0 3 + C 2 
= K 2 + 3CO). 

The annexed figure repre- 
sents the iron retort connected 
with its copper receiver, sur- 
rounded with cold water, and 
containing petroleum to protect 
the distilled potassium from 
oxidation. The lateral tube of 
the receiver permits the tube 
of the retort to be cleared, if 
necessary, during the distilla- 
tion, by the passage of an iron 
rod. 

Some of the most strik- 
ing properties of this metal 
have already been referred 
to (p. 11); its softness, 
causing it to be easily cut 
like wax, the rapidity with 
which its silvery surface 
tarnishes when exposed to the air, its great lightness (sp. gr. 0*865), 
causing it to float upon water, and its taking fire when in contact with 
that liquid, sufficiently distinguish it from other metals. It fuses easily 
when heated, and is converted, at a higher temperature, into a green 
vapour ; if air be present, it burns with a violet-coloured flame, and is 
converted into anhydrous potash, or dipotassium oxide (K 2 0). 

The property of burning with this peculiar violet-coloured flame is 
characteristic of potassium, and allows it to be recognised in its com- 
pounds. 




Fig. 231. — Preparation of potassium. 




Fig. 232. — Coloured flame test. 

If a solution of potassium nitrate (saltpetre) in water be mixed with enough spirit 
of wine to allow of its being inflamed, the flame will have a peculiar lilac colour. 
This colour may also be developed by exposing a very minute particle of saltpetre, 
taken on the end of a heated platinum wire, to the reducing (inner) blowpipe flame 
(fig. 232), when the potassium, being reduced to the metallic state and passing into 
the oxidising (outer) flame in the state of vapour, imparts to that flame a lilac tinge. 



260 EXTRACTION OF COMMON SALT. 

The difficulty and expense attending the preparation of potassium have 
prevented its receiving any application except in purely chemical opera- 
tions, where its attraction for oxygen, chlorine, and other electro-negative 
elements, is often turned to account. 

Potassium chloride (KC1) is an important natural source of this metal, 
being extracted from sea water, from kelp (the ash of sea-weed), and 
from the refuse of the manufacture of sugar from beet-root. It also occurs 
in combination with magnesium chloride, forming the mineral known as 
carnallite (KCl.MgCl 2 .6H 2 0), an immense saline deposit overlying the 
rock-salt in the salt-mines of Stassfurth, in Saxony. Carnallite resembles 
rock-salt in appearance, but is very deliquescent ; it promises to become 
the most important source of potassium hitherto discovered. Considerable 
deposits containing chloride and sulphate of potassium have also been 
found in East Galicia. 

Bicarbonate of potash or hydropotassic carbonate (KHCO B ), which is 
much used in medicine, is obtained by passing carbonic acid gas through 
it strong solution of potassium carbonate, when it is deposited in crystals, 
being much less soluble in water than the normal carbonate. 

Potassium nitrate (KN0 3 ), or saltpetre, will be specially considered 
in the section on gunpowder. 

SODIUM. 

Na' = 23 parts by weight. 

181. Sodium is often found, in place of potassium, in the felspars and 
other minerals, but we are far more abundantly supplied with it in the 
form of common salt (sodium chloride, NaCI), occurring not only in the 
solid state, but dissolved in sea water, and in smaller quantity in the 
waters derived from most lakes, rivers, and springs. 

Rock-salt forms very considerable deposits in many regions; in this 
country the most important is situated at Northwich, in Cheshire, where 
very large quantities are extracted by mining. Wielitzka, in Poland, is 
celebrated for an extensive salt-mine, in which there are a chapel and 
dwelling-rooms, the furniture of which is made of this rock. Extensive 
beds of rock-salt also occur in France, Germany, Hungary, Spain, Abyssinia, 
and Mexico. Perfectly pure specimens form beautiful colourless cubes, 
and are styled sal gem; but ordinary rock-salt is only partially trans- 
parent, and exhibits a rusty colour, due to the presence of iron. In some 
places the salt is extracted by boring a hole into the rock and filling 
it with water, which is pumped up when saturated with salt, and evapo- 
rated in boilers, the minute crystals of salt being removed as they are 
deposited. 

At Droitwich, in Worcestershire, the salt is obtained by evaporation from 
the waters of certain salt springs. In some parts of France and Germany 
the water from the salt springs contains so little salt that it would not 
pay for the fuel necessary to evaporate the water, and a very ingenious 
plan is adopted by which the proportion of water is greatly reduced with- 
out the application of artificial heat. For this purpose a lofty scaffolding 
is erected and filled with bundles of brushwood, over which the salt water 
is allowed to flow, having been raised to the top of the scaffolding by 
pumps. In trickling over the brushwood this water exposes a large sur- 
face to the action of the wind, and a considerable evaporation takes place, 
so that a much stronger brine is collected in the reservoir beneath the 



Extraction of common salt. 261 

scaffolding : by several repetitions of the operation, the proportion of water 
is so far diminished that the rest may be economically evaporated by arti- 
ficial heat. The brine is run into boilers and rapidly boiled for about 
thirty hours, fresh brine being allowed to flow in continually, so as to 
maintain the liquid at the same level in the boiler. During this ebullition 
a considerable deposit, composed of the sulphates of calcium and sodium, 
is formed, and raked out by the workmen. When a film of crystals of salt 
begins to form upon the surface, the fire is lowered, and the temperature of 
the brine allowed to fall to about 180° F., at which temperature it is 
maintained for several days whilst the salt is crystallising. The crystals 
are afterwards drained and dried by exposure to air. The grain of the 
salt is regulated by the temperature at which it crystallises, the size of the 
crystals increasing as the temperature falls. It is not possible to extract 
the whole of the salt in this way, since the last portions which crystallise 
will always be contaminated with other salts present in the brine; but the 
mother-liquor is not wasted, for after as much salt as possible has been 
obtained, it is made to yield sodium sulphate (Glauber's salt), magnesium 
sulphate (Epsom salts), bromine, and iodine. 

The process adopted for extracting the salt from sea water depends 
upon the climate. In Eussia, shallow pits are dug upon the shore in 
which the sea water is allowed to freeze, when a great portion of the 
water separates in the form of pure ice, leaving a solution of salt suffi- 
ciently strong to pay for evaporation. 

Where the climate is sufficiently warm, the sea water is allowed to run 
very slowly through a series of shallow pits upon the shore, where it be- 
comes concentrated by spontaneous evaporation, and is afterwards allowed 
to remain for some time in reservoirs in which the salt is deposited. The 
coarse crystals thus obtained are known in commerce as bay-salt. Eefore 
they are sent into the market they are allowed to drain for a long time, 
in a sheltered situation, when the magnesium chloride with which they 
are contaminated deliquesces in the moisture of the air and drains off. 
The bittern, or liquor remaining after the salt has been extracted, is 
employed to furnish magnesia and bromine. 

Great improvements have been made during the last few years in the economical 
extraction of the salt from sea water. It will be remembered that 1000 parts of 
sea water contain about 

29*0 parts of sodium chloride, 
0'5 ,, potassium chloride, 
3'0 ,, magnesium chloride, 
2 - 5 ,, magnesium sulphate, 
1*5 ,, calcium sulphate, &c. 

In a warm climate, that of Marseilles, for example, the water is allowed to evapo- 
rate spontaneously until it has a specific gravity of 1 *24. During this evaporation 
it deposits about four-fifths of its sodium chloride. It is then mixed with one-tenth 
of its volume of water, and artificially cooled to 0° F. (see p. 127), when it deposits 
a quantity of sodium sulphate, resulting from the decomposition of part of the 
remaining sodium chloride by the magnesium sulphate. The mother-liquor is evapo- 
rated down till its specific gravity is 1 '33,. a fresh quantity of sodium chloride being 
deposited during the evaporation. When the liquid cools it deposits a double salt 
composed of chlorides of potassium and magnesium, from which the latter chloride 
may be extracted by washing with a very little water, leaving the potassium chloride 
fit for the market. 

This process is instructive as illustrating the influence exerted upon the arrange- 
ment of the various acids and bases in a saline solution by the temperature to which 
the solution is exposed, the general rule being that the salt is formed which is least 
soluble in the liquid at the particular temperature. 



262 



MANUFACTURE OF ALKALI. 



The great tendency observed in ordinary table salt to become damp 
when exposed to the air, is due chiefly to the presence of small quantities 
of chlorides of magnesium and calcium, for pure sodium chloride has very 
much less disposition to attract atmospheric moisture, although it is very 
easily dissolved by water, 2 j parts of this liquid being able to dissolve 
one part (by Aveight) of salt. 

In the history of the useful applications of common salt is to be found 
one of the best illustrations of the influence of chemical research upon 
the development of the resources of a country, and a capital example of a 
manufacturing process not based, as such processes usually are, upon mere 
experience, independent of any knowledge of chemical principles, but 
upon a direct and intentional application of these to the attainment of a 
particular object. 



fsiiti 




Fig. 233. — Furnace for converting common salt into sulphate of soda. 

Until the last quarter of the eighteenth century, the uses of common 
salt were limited to culinary and agricultural purposes, and to the glazing 
of the coarser kinds of earthenware, whilst a substance far more useful in 
the arts, carbonate of soda, was imported chiefly from Spain under the 
name of barilla, which was the ash obtained by burning a marine plant 
known as the salsola soda. But this ash only contained about one-fourth 
of its weight of carbonate of soria, so that this latter substance was thus 
imported at a great expense, and the manufactures of soap and glass, to 
which it is indispensable, were proportionally fettered. 

During the wars of the French Eevolution the price of barilla had risen 
so considerably, that it was deemed advisable by Napoleon to offer a 
premium for the discovery of a process by which the carbonate of soda 
could be manufactured at home, and to this circumstance we are indebted 
for the discovery, by Leblanc, of the process at present in use for the 
manufacture of carbonate of soda from common salt, a discovery which 
placed this substance at once among the most important raw materials 
with which a country could be furnished. 

182. Manufacture of carbonate of soda from common salt. — The salt is 

spread upon the hearth of & reverberator ij furnace (fig. 233),* and mixed 

* The hearth of this furnace is usually divided, as seen in the figure, into two compart- 
ments, in one of which (lined with lead), more remote from the grate, the decomposition is 
effected, the acid being poured in through the funnel, while in that nearest to the grate, 
lined with firebrick, the whole of the hydrochloric acid is expelled, and the sodium sulphate 
fused. 



MANUFACTURE OF ALKALI. 263 

with an equal weight of sulphuric acid, which converts it into sodium 
sulphate (p. 157), expelling hydrochloric acid in the form of gas, which 
would prove highly injurious to the vegetation in the neighbourhood, and 
is therefore usually condensed by being brought into contact with water 
(see p. 158). The flame of the fire is allowed to play over the surface of 
the mixture of salt and sulphuric acid until it has become perfectly dry ; 
in this state it is technically known as salt cake, and is next mixed with 
about an equal weight of limestone and rather more than half its weight 
of' small coal ; this mixture is again heated upon the hearth of a reverbera- 
tory furnace, when it evolves an abundance of carbonic oxide, and yields 
a mixture of sodium carbonate with lime and calcium sulphide ; this 
mixture is technically known as hlack ash. 

The chauge which has been effected in the sodium sulphate will be 
easily understood ; for when this salt is heated in contact with carbon 
(from the small coal) it loses its oxygen, and becomes sodium sulphide, 
whilst carbonic acid gas is evolved; thus Na 2 S0 4 + C 2 = lSra 2 S + 2C0 2 . 
Again, when calcium carbonate is heated in contact with carbon, carbonic 
oxide is given off, and lime remains; CaC0 3 + C = 2CO + CaO. Finally, 
when sodium sulphide and lime are heated together in the presence of 
carbonic acid gas, sodium carbonate and calcium sulphide are produced; 
Na 2 S + CaO + C0 2 = Na. 2 C0 8 + CaS . 

When the black ash is treated with water, the sodium carbonate is 
dissolved, leaving the calcium sulphide, and by evaporating the solution, 
ordinary soda ash is obtained.* But this is by no means pure sodium 
carbonate, for it contains, in addition to a considerable quantity of common 
salt and sodium sulphate, a certain amount of caustic soda, formed by 
the action of the excess of lime upon the carbonate. In order to purify 
it, the crude soda ash is mixed with small coal or sawdust and again 
heated, when the carbonic acid gas formed from the carbonaceous matter 
converts the caustic soda into carbonate, and on dissolving the mass in 
water and evaporating the solution, it deposits oblique rhombic prisms of 
common washing soda, having the composition Na 2 CO 3 .10Aq. [soda 
crystals). 

A little reflection will show the important influence which this process 
has exerted upon the progress of the useful arts in this country. The 
three raw materials, salt, coal, and limestone, we possess in abundance. 
The sulphuric acid, when the process was first introduced, bore a high 
price, but the resulting demand for this acid gave rise to so many im- 
provements in its manufacture that its price has been very greatly 
diminished — a circumstance which has of course produced a most beneficial 
effect upon all branches of manufacture in which the acid is employed. 

The large quantity of hydrochloric acid obtained as a secondary pro- 
duct has been employed for the preparation of bleaching powder, and 
the important arts of bleaching and calico-printing have thence received 
a considerable impulse. These arts have also derived a more direct 
benefit from the increased supply of sodium carbonate, which is so largely 
used for cleansing all kinds of textile fabrics. The manufactures of soap 
and glass, which probably create the greatest demand for sodium 
carbonate, have been increased and improved beyond all precedent by the 
production of this salt from native sources. 

* Before evaporation, air is generally blown through the liquor to oxidise the sodium 
sulphide which may remain unaltered. 



264 EECOVERY OF SULPHUR FROM ALKALI WASTE. 

Hargreave's process dispenses with the use of sulphuric acid, and converts the 
sodium chloride into sulphate by the action of sulphurous acid gas (obtained by 
burning pyrites) steam, and air, at a dull red heat — 

2NaCl + H 2 + S0 2 + = Na 2 S0 4 + 2HC1. 
The hydrochloric acid is absorbed by water, as usual, and the sodium sulphate 
converted into carbonate as described above. 

Deacon passes chlorine, sulphurous acid gas, and steam over the salt, which is made 
to glide down a series of inclined planes in a tower strongly heated ; S0 2 + 2H 2 
+ C1 2 = 2HC1 + H. 2 S0 4 . The HC1 is condensed and employed for the production of 
chlorine, whilst the H 2 S0 4 decomposes the NaCl . 

In the ammonia soda process which is now much used, a strong solution of NaCl is 
decomposed by the bicarbonate of ammonia, when bicarbonate of soda is deposited as 
a crystalline powder, leaving ammonium chloride in the solution ; NaCI + NH 4 HC0 3 
= NH 4 C1 + NaHC0 3 . The bicarbonate of soda is heated to convert it into carbonate ; 
2NaHC0 3 = Na 2 C0 3 +H 2 + C0 2 . The ammonium chloride is heated with lime to 
disengage the ammonia which is then converted into bicarbonate by the C0 2 (in the 
presence of water), so that the same ammonia is used over again. 

The sodium carbonate obtained by the ammonia process is much prized by the 
glass manufacturer on account of its purity. 

Recovery of sulphur from alkali-waste. — Since nearly the whole of the sulphur 
which is employed, in the form of sulphuric acid, for decomposing the common salt, 
is obtained at the alkali-works in the form of calcium sulphide in the tank-waste 
left after exhausting the black ash with water, several processes have been devised 
for recovering the sulphur in order to employ it again for the manufacture of oil of 
vitriol. The simplest of these consists in blowing air through the moist tank-waste, 
until it is converted into a mixture of calcium disulphide and calcium hyposulphite, 
the oxidation being stopped when one-third of the disulphide has been converted 
into hyposulphite — 

(1) 2CaS + = CaO + CaS 2 . (2) CaS 2 + 3 = CaS 2 3 . 
When the yellow liquor thus obtained is decomposed by the muriatic acid from the 
alkali-works the sulphur is precipitated — 

(2) CaS 2 3 + 2CaS 2 + 6HC1 - S 6 + 3CaCl 2 + 3H 2 0. 

In another process, the drainings from the heaps of alkali-waste exposed to rain 
are saturated with sulphurous acid, gas from burning pyrites, when calcium hypo- 
sulphite is formed, and, on adding muriatic acid, both the sulphur of the waste and 
that obtained from the pyrites are precipitated. 

An objection to these processes appears to be the difficulty in procuring a sufficient 
quantity of muriatic acid, for which there is a great demand on the part of the pro- 
ducers of bleaching powder and bicarbonate of soda. 

Another process for recovering the sulphur employs the waste liquor from the 
chlorine stills (see p. 148), which contains manganese dichloride (MnCl 2 ) and ferric 
chloride (Fe 2 Cl 6 ). On treating the calcium sulphide in the soda- waste with this still- 
liquor, calcium chloride and sulphides of iron and manganese are produced — 
MnCl 2 + CaS = MnS + CaCl 2 ; Fe 2 Cl 6 + 3CaS = Fe 2 S 3 + 3CaCl 2 . 

By exposing these sulphides to the air, in a moist state, the sulphur is separated, 
and the metals are converted into oxides — 

2MnS + 8 = Mn 2 3 + S 2 ; Fe 2 S 3 + 3 = Fe 2 3 + S 3 . 

By stirring these oxides with more soda-waste, the sulphides-are reproduced ; and 
are afterwards again oxidised by exposure to air so as to separate their sulphur. 
The sulphur thus separated combines with the calcium sulphide in a fresh portion of 
the waste, to form disulphide, one-third of which is oxidised by the air, as in the 
process first described, and converted into calcium hyposulphite. In order to pre- 
cipitate the sulphur from the liquor containing the calcium disulphide and calcium 
hyposulphite, the excess of hydrochloric acid always present in the chlorine still- 
liquor is turned to account ; the sulphur liquor is run into this until the precipitated 
sulphur begins to be accompanied by a black precipitate of sulphide of iron, showing 
that all the free acid has been neutralised. The still-liquor thus neutralised is then 
employed for decomposing a fresh portion of the soda-waste, as at the commencement 
of the process. The precipitated sulphur is pressed to free it from the liquor, dried, 
and melted by super-heated steam. 

Although the chemistry of this process is rather elaborate, the practical working is 
said to be very simple and inexpensive. 



SODA LYE — SODIUM. 265 

The most recently invented process for extracting sulphur from tank- waste consists 
in decomposing the calcium sulphide in the waste with a strong solution of magnesium 
chloride ; CaS + MgCl 2 + H 2 = CaCl 2 + MgO + H 2 S. The H 2 S is burnt, and the S0 2 
formed is converted into H 2 S0 4 in the vitriol chambers (p. 204). 

In order to recover the magnesium chloride, "the mixture of CaCl 2 and MgO is 
treated, under pressure, with carbonic acid gas obtained from a lime kiln ; CaCl 2 
+ MgO + C0 2 — CaC0 3 + MgCl 2 . The magnesium chloride may therefore be used over 
and over again. 

The crystals of sodium carbonate are easily distinguished by their pro- 
perty of efflorescing in dry air (p. 42), and by their alkaline taste, which 
is much milder than that of potassium carbonate, this being, moreover, a 
deliquescent salt. The crystals are very soluble in water, requiring only 
2 parts of cold, and less than their own weight of boiling water ; the 
solution is strongly alkaline to test-papers. 

The substance commonly used in medicine under the name of carbonate 
of soda, is really the bicarbonate (or hydrosodic carbonate, NaHC0 3 ), and 
is prepared by saturating the carbonate with carbonic acid gas. It is 
readily distinguished from the carbonate, as it is but slightly alkaline, and 
is very much less easily dissolved by water. 

Soda lye, employed in the manufacture of hard soap, is a solution 
of sodium hydrate (NaHO), obtained by decomposing the carbonate 
with calcium hydrate (slaked lime), Na 2 C0 3 + Ca(HO) 2 = 2NaHO 
+ CaC0 8 . 

The solid sodium hydrate of commerce is generally obtained in the 
process for manufacturing carbonate of soda just described : the solution 
obtained by treating the black ash with water is concentrated by evapora- 
tion, so that the carbonate, sulphate, and chloride of sodium may 
crystallise out, leaving the hydrate, which is far more soluble, in the 
liquid. The latter, which still contains a compound of sulphide of 
sodium and sulphide of iron, which gives it a red colour (red liquor) is 
mixed with some nitrate of soda to oxidise the sulphides, and evaporated 
down until a fused mass of sodium hydrate is left, which is poured out 
into iron moulds.* 

Kryolite (Na 3 AlF 6 ) is sometimes employed as a source of the sodium 
hydrate which may be obtained by decomposing it with slaked lime. 

183. Sodium. — Potash and soda exhibit so much similarity in their 
properties, that we cannot be surprised at their having been confounded 
together by the earlier chemists, and it was not till 1736 that Du Hamel 
pointed out the difference between them. The discovery of potassium 
naturally led Davy to that of sodium, which can be obtained by processes 
exactly similar to those adopted for procuring potassium, to which it will 
be remembered sodium presents very great similarity in properties (p. 12). 
Sodium, however, is readily distinguished from potassium by its burning 
with a yellow flame, which serves even to characterise it when in 
combination. 

This yellow flame is well seen by dissolving salt in water in a plate, and adding 
enough spirit of wine to render it inflammable, the mixture being well-stirred while 
burning. If a little piece of sodium be burnt in an iron spoon held in a flame, all 

* Another plan of treating the black ash liquor consists in allowing it to trickle through 
a column of coke against a current of air, when the sodium sulphide is oxidised, whilst 
the sulphide of iron is deposited. The liquor is mixed with a little chloride of lime to 
oxidise any remaining sulphides, and concentrated by evaporation, when carbonate and 
ferrocyanide of sodium are deposited in crystals. The liquor separated from these 
contains the sodium hydrate, and is evaporated till it solidifies on cooling. 



266 SODIUM — BORAX. 

the flames in the room, even at a remote distance, will be tinged yellow The blow- 
pipe ilame may also be employed to detect sodium by this colour, as in the case of 
potassium (p. 259). In fireworks, nitrate of soda is employed for producing yellow 
flames. A very good yellow fire may be made by intimately mixing, in a mortar, 
74 grs. of nitrate of soda, 20 grs. of sulphur, 6 grs. of sulphide of antimony, and 
2 grs. of charcoal, all carefully dried, and very finely powdered. 

The preparation of sodium, by distilling a mixture of sodium carbonate 
and charcoal, is much easier than that of potassium, for which reason 
sodium is far less costly than that metal, and has received applications, 
on the large scale, during the last few years, for the extraction of the 
metals aluminium and magnesium. An amalgam of sodium (p. 131) is 
also employed with advantage in extracting gold and silver from their 
ores. To obtain sodium in large quantity, a mixture of dried carbonate 
of soda, powdered coal, and chalk is distilled in iron cylinders, when the 
sodium passes over in the form of vapour— 

Na 2 C0 3 + C 2 = Na 2 + 3CO. 

The chalk is employed to prevent the fusion of the mixture. 

184. Borax, biborate of soda (Na 2 0.2B 2 3 or Na 2 B 4 7 ). — A very im- 
portant compound of soda is used in the arts under the name of borax, in 
which the soda is combined with boracic anhydride. It has already been 
stated that this substance' is deposited during the evaporation of the 
waters of certain lakes in Thibet, whence it is imported into this country 
in impure crystals, which are covered with a peculiar greasy coating. 
Borax has also been found abundantly in Southern California. The 
refiner of tincal powders the crystals and washes them, upon a strainer, 
with a weak solution of soda, which converts the greasy matter into a 
soap and dissolves it. The borax is then dissolved in water, a quantity 
of sodium carbonate is added to separate some lime which the borax 
usually contains, and, after filtering off the carbonate of lime, the solution 
is evaporated to the crystallising point and allowed to cool, in order that 
it may deposit the pure crystals of borax. 

It appears, however, that the greater part of the borax employed in the 
arts is manufactured in this country by heating carbonate of soda with 
boracic acid, when the latter expels the carbonic acid and combines with 
the soda.* The mass is then dissolved in water, and the borax crystal- 
lised, an operation upon which much care is bestowed, since the product 
does not meet with a ready sale unless in large crystals, 

The solution of borax, having been evaporated to the requisite degree 
of concentration, is allowed to crystallise in covered wooden boxes, which 
are lined with lead and enclosed in an outer case of wood, the space 
between the sides of the case and the box being stuffed with some bad 
conducter of heat, so that the solution of borax may cool very slowly, and 
large crystals may be deposited. In about thirty hours the crystallisa- 
tion is completed, when the liquid is drawn off as rapidly as possible, the 
last portion being carefully soaked up with sponges, so that no small 
crystals may be afterwards formed upon the surface of the large ones ; the 
case is then again covered up, so that the crystals may cool slowly with- 
out cracking. 

* The ammonia which is evolved from the Tuscan boracic acid employed in this process 
is known in commerce as Volcanic ammonia, and is free from the empyreumatic odour 
which generally accompanies that from coal and bones. 



SODIOI SILICATE. 267 

Borax is chemically known as sodium anhydroborate, and is represented, 
in the dry state, by the formula Xa B 4 7 . The ordinary prismatic crystals, 
however, contain ten molecules of water of crystallisation, and are 
therefore represented by the formula Xa o B 4 O r .10Aq. They soon effloresce 
and become opaque when exposed to air, and may readily be distinguished 
by their alkaline taste and action upon test-papers, and especially by their 
behaviour when heated, for they fuse easily and intumesce most violently, 
swelling up to a white spongy mass of many times their original bulk; 
this mass afterwards fuses down to a clear liquid which forms a trans- 
parent glassy mass on cooling {vitrified borax), and since this glass is 
capable of dissolving many metallic oxides with great readiness (borax 
being, by constitution, an acid salt, and therefore ready to combine -with 
more base), it is much used in the metallurgic arts. Large quantities of 
borax are also employed in glazing ston^Tare. 

185. Sodium silicate. — A combination of soda with silica has long- 
been used, under the name of soluble glass, for imparting a fire-proof 
character to wood and other materials, and more recently, for producing 
artificial stone for building purposes, and for a peculiar kind of permanent 
fresco-painting (stereocJiromy), the results of which are intended to with- 
stand exposure to the weather. 

Soluble glass is usually prepared by fusing 15 parts of sand with 8 
parts of carbonate of soda and 1 part of charcoal. The silicic acid, com- 
bining with the soda, disengages the carbonic acid gas, the expulsion of 
which is facilitated by the presence of charcoal, which converts it into 
carbonic oxide. The mass thus formed is scarcely affected by cold water, 
but dissolves when boiled with water, yielding a strongly alkaline liquid. 

In using this substance for rendering wood fire-proof, a rather weak 
solution is first applied to the wood, and over this a coating of lime-wash 
is laid, a second coating of soluble glass (in a more concentrated solu- 
tion) is then applied. The wood so prepared is, of course, charred, as 
usual, by the appli2ation of heat, but its inflammability is remarkably 
diminishecl. 

For the manufacture of Mansome's artificial stone, the soluble glass is 
prepared by heating flints, under pressure, with a strong solution of 
caustic soda, to a temperature between 300° and 400° F., when the silica 
constituting the flint enters into combination with the soda. Finely 
divided sand is moistened with this solution, pressed into moulds, dried, and 
exposed to a high temperature, when the silicate of soda fuses and cements 
the grains of sand together into a mass of artificial sandstone, to which 
any required colour may be imparted by mixing metallic oxides with the 
sand before it is moulded. 

Silicate of soda is also sometimes used as a dung substitute (p. 242) in 
calico-printing. 

Sodium sulphate forms the very common saline efflorescence upon the 
surface of brick walls, and has been found covering the sandy soil of 
the Desert of Atacama. over a considerable area. The mineral known 
as Thenardite also consists of sodium sulphate, and Glauberite is a 
double sulphate of sodium and calcium (Xa 2 S0 4 .CaS0 4 ) which is nearly 
insoluble in water. 

Phosphate of soda or hydrodisodic orthophosphate, Xa o HP0 4 .12Aq., 
is obtained by neutralising, with sodium carbonate, the impure phosphoric 



2(58 SALTS OF AMMONIUM. 

acid obtained by decomposing bone-ash with sulphuric acid (p. 229). On 
evaporation, the phosphate is deposited in oblique rhombic prisms which 
effloresce in air. 

Sodium nitrate, NaN0 3 , will be more particularly noticed in the 
section on gunpowder. It is imported from Peru, and used in consider- 
able quantity as a manure, and for the manufacture of potassium nitrate. 

SALTS OF AMMONIUM. 

186. The great chemical resemblance between some of the salts formed 
by neutralising acids with ammonia, and the salts of potassium and sodium, 
has been already pointed out as affording a reason for the hypothesis of 
the existence of a compound metal, ammonium (NHJ, equivalent in its 
functions to potassium and sodium. 

The compounds which are formed when ammonia (NHJ combines with 
the anhydrides, such as carbonic (C0 2 ) and sulphuric (S0 3 ), do not exhibit 
the resemblance to the salts of potassium and sodium until water is added. 
Thus, by the action of dry ammonia gas upon sulphuric anhydride, a 
compound called sulphuric ammonide is formed, having the composition 
(NH 3 ) 2 S0 3 . This substance dissolves in water and crystallises in octahedra, 
but its solution is not precipitated by barium chloride, which always pre- 
cipitates the true sulphates, nor by platinic chloride which precipitates the 
true ammonium salts. By long boiling with water, however, it becomes 
converted into ammonium sulphate (NH 4 ) 2 S0 4 , which yields precipitates 
with both the above tests. The phosphoric, carbonic, and sulphurous 
anhydrides also combine with dry ammonia to form ammonides, which 
do not respond to the ordinary tests for the corresponding salts of 
ammonium until after water has been assimilated. The true salts of 
ammonium are produced either by the combination of an acid with 
ammonia, or by double decomposition. 

187. Ammonium sulphate, (NH 4 ) 2 S0 4 , is largely employed in the pre- 
paration of ammonia-alum, and of artificial manures, for which purposes 
it is generally obtained from the ammoniacal liquor of the gas-works by 
neutralising with sulphuric acid and evaporating. The rough crystals are 
gently heated to expel tarry substances, and purified by recrystallisation. 
The crystals have the same shape as those of potassium sulphate, and are 
easily soluble in water. When heated to about 500° F. the ammonium 
sulphate is decomposed, yielding vapour of ammonium sulphite, water, 
ammonia, nitrogen, and sulphur dioxide. If muslin be dipped into a 
solution of ammonium sulphate in ten parts of water and dried, it will no 
longer burn with flame when ignited. The mineral mascagnine consists 
of ammonium sulphate. This salt is occasionally found in needle-like 
crystals upon the windows of rooms in which coal gas is burnt. 

1 88. Sesquicarbonate of ammonia* (4KH 3 . 3H 2 0. 3C0 2 or (KH 4 ) 4 H 2 (C0 3 ) 3 
is the common carbonate of ammonia of the shops, also called smelling 
salts or Preston salts, largely used in medicine, and by bakers and con- 
fectioners, for imparting lightness or porosity to cakes, &c. It is com- 
monly prepared by mixing sal ammoniac (ammonium chloride) with twice 
its weight of chalk, and distilling the mixture in an earthen or iron 

* It appears that the carbonate formerly found in commerce had the composition 
4NH 3 .2H 2 0.3C0 2 . 



SAL AMMONIAC. 2B9 

retort, communicating, through an iron pipe, with a leaden chamber or 
receiver, in which the ammonium carbonate collects as a transparent 
fibrous mass, which is extracted by taking the receiver to pieces, and 
purified by resubliming it at about 130° F., in iron vessels surmounted by 
leaden domes. The action of calcium carbonate upon ammonium chloride 
would be expected to furnish the normal carbonate (NH 4 ) 2 C0 3 , but this 
salt (even if produced) is decomposed by the heat employed in the 
process — 

6NH 4 C1 + 3CaC0 3 = 2KET 3 + 3CaCl 2 + (NTi 4 ) 4 H 2 (C0 3 ) 3 . 

When a mass of freshly prepared sesquicarbonate of ammonia is 
exposed to air, it evolves ammonia and becomes gradually converted into 
an opaque crumbly mass of bicarbonate of ammonia or hydroammonic 
carbonate— 

(NH 4 ) 4 H 2 (C0 3 ) 3 = ]\ T H 3 + 3NH 4 HCO s . 

Water effects this decomposition more rapidly ; if the powdered sesqui- 
carbonate of ammonia be washed with a little water, bicarbonate of am- 
monia is left, and the solution contains the normal carbonate (NH 4 ) 2 C0 3 , 
which may be obtained in crystals by adopting certain precautions. The 
sesquicarbonate dissolves in about three times its weight of cold water. 
Boiling water decomposes it, and the solution, on cooling, deposits large 
prismatic crystals of bicarbonate of ammonia (NH 4 HC0 3 ) which is much 
less soluble in water. This salt has been found in considerable quantity, 
forming crystalline masses in a bed of guano on the western coast of 
Patagonia. Sal volatile is an alcoholic solution of carbonate of ammonia 
obtained by distilling sal ammoniac with carbonate of potash and rectified 
spirit of wine, or by treating the sesquicarbonate of ammonia with hot 
spirit. 

The commercial carbonate of ammonia appears to contain a small quantity of 
ammonium carbamate, N H 4 CO,NH 2 , which is derived from the normal carbonate by 
the loss of H 2 ; (NH 4 ) 2 C0 3 = NH 4 C0. 2 NH. 2 + H 2 0. 

The ammonium carbamate is deposited as a white solid when ammonia gas is mixed 
with carbonic acid gas. It may be obtained in crystals by passing C0 2 and NH 3 
into the strongest solution of ammonia. 

Ammonium carbamate is easily soluble in water, which soon converts it into am- 
monium carbonate. The aqueous solution, when freshly prepared, is not precipitated 
by calcium chloride, but the calcium carbonate is deposited on standing or heating. 

When ammonium carbamate is heated in a sealed tube to 130° C. it is decomposed 
into ammonium carbonate and urea, 2NH 4 C0 2 lSrH 2 = (NH 4 ) 2 C03 + CO]Sr 2 H 4 . Car- 
bamic acid, HC0 2 ]SrH 2 , has not been isolated ; its relation to carbonic acid is seen by 
a comparison of their formulae — 

CO S 0H CO J 0H 

CU I OH L0 j NH 2 

Hypothetical carbonic acid. Hypothetical carbamic acid. 

Other carbamates have been obtained by passing C0 2 through strongly ammoniacal 

solutions of different bases, and precipitating the carbamates by alcohol. "When 

potassium carbamate is heated, it yields water and potassium cyanate, KC0 NH., 

= KCXO + H 2 0. 

189. Ammonium chloride (NH 4 C1), also called muriate of ammonia and 
sal ammoniac— When dry ammonia gas is brought in contact with an 
equal volume of dry hydrochloric acid gas, it has been seen (p. 130) that 
they combine directly to produce this salt, the preparation of which on 
the large scale has been noticed at p. 124. It is also sometimes made by 
subliming a mixture of ammonium sulphate with common salt — 
(NH 4 ) 2 S0 4 + 2^aCl = 2XH 4 C1 + Xa 2 S0 4 . 



270 SULPHIDE OF AMMONIUM. 

Its commercial form is that of a very tough translucent fibrous mass, 
generally of the dome-like shape of the receivers, and often striped with 
brown, from the presence of a little iron. It has not the least smell of 
ammonia, and is very soluble in water, requiring about three parts of cold 
water, and little more than its own weight of boiling water. As the hot 
solution cools, it deposits beautiful fern-like crystallisations composed of 
minute cubes and octahedra. The liquefaction of sal ammoniac in water 
lowers the temperature very considerably, which renders the salt very 
useful in freezing mixtures. A mixture of equal weights of sal ammoniac 
and nitre, dissolved in its own weight of water, lowers the temperature 
of the latter from 50° F. to 10°. In this case partial decomposition takes 
place, resulting in the production of potassium chloride and ammonium 
nitrate, both of which absorb much heat whilst being dissolved by water. 
The solution of ammonium chloride in water is slightly acid to blue 
litmus paper. When sal ammoniac is heated, it passes off in vapour, at a 
temperature below redness, without previously fusing ; the vapour forms 
thick white clouds in the air, and may be recondensed as a white crust 
upon a cold surface ; but it cannot be sublimed without some loss, a 
portion being decomposed into hydrochloric acid, hydrogen, and nitrogen. 
The specific gravity (weight of 1 volume) of the vapour of sal ammoniac 
is 13*3 times that of hydrogen, so that 5 3 -5 parts, or one molecule, would 
appear to occupy 4 volumes instead of 2, but this may be explained by 
supposing a temporary dissociation of the hydrochloric acid and ammonia 
when the salt is converted into vapour, so that the observed specific 
gravity is really that of a mixture of equal volumes of these constituent 
gases. Experimental evidence has been obtained in support of this 
view, for it has been found that free ammonia and hydrochloric acid may 
be separated by diffusion from the vapour obtained on heating ammonium 
chloride. 

This may he shown by placing a fragment of sal ammoniac in a narrow test-tube, 
with a plug of asbestos at a little distance above it ; if a piece of red litmus paper be 
placed in the tube, it will be found, on heating the sal ammoniac and the asbestos, 
that the NH 3 , being lighter, diffuses most rapidly through the asbestos, and blues 
the red litmus, but soon afterwards the hydrochloric acid diffuses through, and the 
litmus is again reddened. 

Moreover, the heat which becomes latent or is absorbed in vaporising 
the sal ammoniac, is almost exactly that which is produced by the com- 
bination of the hydrochloric acid and ammonia. 

When ammonium chloride is heated with metallic oxides, the hydro- 
chloric acid often converts the oxide into a chloride which is either fusible 
or volatile, so that sal ammoniac is often employed for cleansing the sur- 
faces of metals previously to soldering them. Even those metallic oxides 
which are destitute of basic properties, such as antimonic and stannic 
oxides, are convertible into chlorides by the action of sal ammoniac at a. 
high temperature. 

Ammonium chloride is found in volcanic districts, and is present in 
very small quantity in sea water. 

190. Hydrosulphate of ammonia (2N"H 3 .H. 2 S), or ammonium sulp?dde 
(NH 4 ) 2 S, has been obtained in colourless crystals by mixing hydrosulphuric 
acid gas with twice its volume of ammonia gas in a vessel cooled by a 
mixture of ice and salt. It is a very unstable compound, decomposing at 
the ordinary temperature of the air into free ammonia and ammonium 



SULPHIDES OF AMMONIUM. 271 

hydrosulphide, NH 4 HS, which, may be obtained in very volatile colourless 
needles by passing equal volumes of NH 3 and H 2 S into a vessel cooled in 
ice. When a solution of ammonia is saturated with hydric sulphide, the 
ammonia is found to have combined with one molecule, forming a solution 
of the ammonium hydromlphide (NH 4 HS). The solution is colourless 
when freshly prepared, but it soon becomes yellow in contact with the air, 
from the formation of ammonium disulphide (NH 4 ) 2 S 2 , ammonium hypo- 
sulphite being formed at the same time — 

4NH 4 HS + 5 = (KH 4 ) 2 S 2 + (NH 4 ) 2 S 2 3 + 2H 2 0. 

Eventually, the solution deposits sulphur and becomes colourless, hypo- 
sulphite, sulphite, and sulphate of ammonium being formed. When the 
freshly-prepared colourless solution of ammonium hydrosulphide is mixed 
with an acid, the solution remains clear, hydrosulphuric acid being evolved 
with effervescence ; NH 4 HS + HC1 = NH 4 C1 -I- H 2 S ■ but if the solution 
be yellow, a milky precipitate of sulphur is produced, from the decom- 
position of the ammonium disulphide — 

(NH 4 ) 2 S 2 + 2HCI = 2NH 4 C1 + H 2 S + S. 

The fresh solution gives a black precipitate of lead sulphide when 
solution of lead acetate is added to it, but after it has been kept till it 
is of a dark yellow or red colour, it gives a red precipitate of the per- 
sulphide of lead. Solution of ammonium sulphide, prepared by mixing 
the hydrosulphide with an equal volume of solution of ammonia, is Jargely 
employed in analytical chemistry ; NH 4 HS + NH 3 = (NH 4 ) 2 S . The 
solution has a very disagreeable odour. 

Ammonium disulphide is obtained in deliquescent yellow crystals, when a mixture 
of ammonia gas with vapour of sulphur is passed through a red hot porcelain tube. 
It is the chief constituent of Boyle's fuming liquor, a fetid yellow liquid obtained by 
distilling sal ammoniac with sulphur and lime. The disulphide is sometimes 
deposited in yellow crystals from this liquid. By dissolving sulphur in ammonium 
disulphide, orange-yellow prismatic crystals of ammonium pentasulpjliide (NH 4 ) 2 S 5 
may be obtained. Even a heptasulphide (JSTH) 2 S 7 has been crystallised. 

It is scarcely possible to represent the constitution of the higher sulphides of 
ammonium except on the ammonium hypothesis. 

Ammonium bromide (NH 4 Br), and ammonium iodide (NH 4 T), are useful in pho- 
tography. They are both colourless crystalline salts, but the iodide is very liable 
to become yellow or brown, from the separation of iodine, unless kept dry and in 
the dark. Both salts are extremely soluble in water. 

191. Lithium (L = 7 parts by weight) is a comparatively rare metal, obtained chiefly 
from the minerals lepidolite (teiris, a scale) or lithia-mica, containing silicate of 
alumina with fluorides of potassium and lithium ; petalite (ireraXov, a leaf), silicate of 
soda, lithia, and alumina, and triphane or spodumene (airoSbs, ashes), which has a 
similar composition. Its name (from \l6os, a stone) was bestowed in the belief that 
it existed only in the mineral kingdom, but recent investigation has detected it in 
minute proportion in the ashes of tobacco and other plants. 

Metallic lithium is obtained by decomposing fused lithium chloride by a galvanic 
current. It is remarkable as the lightest of the solid elements (sp. gr. 0'59). It 
bears a general resemblance to potassium and sodium, but it is harder and less easily 
oxidised than those metals. It decomposes water rapidly at the ordinary temperature, 
but does not inflame upon it. 

Lithium differs from potassium and sodium by forming a sparingly soluble 
phosphate (L 3 P0 4 ) and carbonate (L 2 C0 3 ). The compounds of lithium impart a red 
colour to the flame of the blowpipe (p. 259). 

Lithium carbonate is occasionally employed medicinally. 

Rubidium (Rb' = 85 parts by weight) and Cesium (Cs' = 133 parts by weight) 
were discovered so lately as in 1860, by Bunsen and Kirchhoff, during the analysis 



272 



SPECTRUM ANALYSIS. 



of a certain spring water which contained these metals in so minute quantity (2 or 3 
grs. in a ton) that they would certainly have escaped observation if the analysis had 
been conducted in the ordinary way. The discovery of these metals, as well as of 
three others (thallium, indium, gallium) to be mentioned hereafter, was the result of 
the application of the method of spectrum analysis, of which a brief description is 
here given, although the discussion of the optical principles upon which it depends 
would be misplaced in a chemical work. 

192. Spectrum analysis. — It has been mentioned above that compounds 
of potassium, sodium, and lithium impart, respectively, lilac, yellow, and 
red colours to the blowpipe flame (or air-gas flame, see p. 107), or, in 
other words, that the highly heated vapours of the metals evolve luminous 
rays of these particular colours. When the quantity of the metal is 
extremely minute, and its peculiar luminous rays proportionally scanty, 
their colour may very easily escape notice, especially if two or three metals 
are present in the flame at the same time. But if the light emanating 

from the flame be allowed to 
pass through a narrow slit 
at A (fig. 234), collected by 
a lens, and transmitted 
through a prism of flint 
glass or through a hollow 
prism (B) filled with carbon 
disulphide, all the rays of one 
colour will be refracted in a 
definite direction, so that the 
spectrum, or image of the 
slit, when thrown upon a 
screen, instead of exhibiting 
colours uniformly distributed like the flame itself, will show stripes or 
bands of the various coloured rays existing in the flame. Thus, when 
vapour of sodium is present in the flame, the whole of the yellow light 
emitted by it will be collected in the spectimmmto a narrow yellow stripe 
of great intensity, and so extremely delicate is this test that it is scarcely 
possible to obtain a flame which does not exhibit this sodium line. The 
heated vapour of lithium emits a mixture of red with a few yellow rays, 
and accordingly, the spectrum of a flame containing lithium exhibits a very 
bright band of red light, and a comparatively dull band of yellow light, 
the red band being characteristic of lithium. The potassium flame emits 
a mixture of blue and red rays, so that its spectrum exhibits a distinct 
red band of a darker colour than the lithium band, and a feeble violet 
band. Instead of throwing the spectrum upon a screen, it is generally 
passed through a telescope (C) to the eye of the observer, and the spectro- 
scope so constructed has now taken its place among the apparatus indis- 
pensable to the analytical chemist. The prism B may be slowly moved 
round by a handle attached to a stage on which it rests, in order that the 
different parts of the spectrum may be successively brought into sight. 
By comparing the spectra of the flames containing vapours of the metals 
with a picture or map of the solar spectrum (fig. 235), the exact position 
of the various coloured bands may be noted, and thus, if several metals 
are present in the same flame, they may still be distinguished by the 
colours and positions of their bands. Thus, if a mixture of the chlorides 
of potassium, sodium, and lithium be taken upon a loop of platinum wire 
and held in the flame, the dull red line of potassium (K, fig. 235) is seen 




Spectroscope. 



RUBIDIUM — CAESIUM. 



273 



close to one end of the spectrum; at some distance from it the bright red 
band (L) of lithium; at about the same distance from this, the pale 
yellow lithium line ; and close to this, the bright yellow band of 
sodium (Na) ; whilst near to the other end of the spectrum is the feeble 
violet band of potassium (k). The chlorides of the metals are most 
suitable for this experiment, on account of their easy conversion into 
vapour. 



Violet. Indicjo. Ulize 



Green. 



Yellow. Orange. Reel/. 




Spectrum furnished by solar light decomposed by a prism. 







, 












6 






e s 


«" 


S * a 


* . b 


c 


B 3 


-b -B gig &*•§•§ 

5 ^ £*~ ,» B 35'S 


"■8 £4 


,3 




£ 

« 




3 U/2 


fi 8 




e 


^ 


<* 


<o 




K 


t 


3 


2 


i 












A 


a 




1 


K. 




Coloured bands in the spectru 


tn. 












Fig. 235. 





















When examining, with the spectroscope, the alkaline chlorides extracted from the 
spring water above alluded to, Bunsen and Kirchhoff observed two red and two blue 
bands in the spectrum, which they could not ascribe to any known substance, and 
which they ultimately traced to the two new metals, rubidium {rubidus, dark-red) 
and caesium (cassius, sky-blue). 

Rubidium has since been found in small quantity in other mineral waters, in 
lepidolite, and in the ashes of many plants. This metal is closely related in pro- 
perties to potassium, but is more easily fusible and convertible into vapour, and 
actually surpasses that metal in its attraction for oxygen, rubidium taking tire 
spontaneously in air. It burns on water with exactly the same flame as potassium. 
Its hydrate is a powerful alkali, like potash, and its salts are isomorphous with those 
of potash. The double chloride of platinum and potassium, however, is eight times 
as soluble in boiling water as the corresponding salt of rubidium, which is taken 
advantage of in separating these two allied metals. 

Caesium appears to be, even more highly electro-positive than rubidium, forming a 
strong alkali, caesium hydrate, and salts which are isomorphous with those of potas- 
sium. Caesium carbonate, however, is soluble in alcohol, which does not dissolve 
the carbonates of potassium and rubidium. Moreover, the caesium bitartrate is nine 
times as soluble in water as the rubidium bitartrate. 

Caesium has been found in lepidolite ; and the rare mineral pollux found in Elba, 
and resembling felspar in composition, is said to contain a very large quantity of 
this metal. 

Metallic caesium cannot be obtained by reduction with carbon, but it has been 
extracted by decomposing its cyanide by the galvanic current. 

193. General review of the group of alkali metals.— Caesium, rubidium, 
potassium, sodium, and lithium constitute a group of elements conspicuous 
for their highly electro-positive character, the powerfully alkaline nature of 

S 



274 BARIUM. 

their hydrates, and the general solubility of their salts. Their chemical 
characters and functions are directly opposite to those of the electro- 
negative group containing fluorine, chlorine, bromine, and iodine, and, 
like those elements, they exhibit a gradation of properties. Thus, caesium 
appears to be the most highly electro-positive member, rubidium the next, 
then potassium and sodium, whilst lithium is the least electro-positive ; 
and just as iodine, the least electro-negative of the halogens, possesses 
the highest atomic number, so caesium, the least electro-negative (or most 
electro-positive) of the alkali-metals, has a higher atomic weight than any 
other member of this group, their atomic weights being represented by 
the numbers, caesium, 133; rubidium, 85*3; potassium, 39; sodium, 23; 
lithium, 7. As in the case of the halogens also, these are all univalent 
elements. Just as chlorine is accepted as the representative of chlorous 
radicals, so potassium is commonly regarded as the type of basylous radicals, 
the term radical being applied to all substances, whether elementary or 
compound, which are capable of being transferred, like chlorine or 
notassium, from one compound to another without suffering decomposition. 

Some of the physical properties of these elements exhibit a gradation in 
the same order as their atomic weights ; thus caesium fuses at 80° F., rubid- 
ium at 101°, potassium at 144°"5, sodium at 207 o, 7, and lithium at 356°, so 
that, at ordinary temperatures, rubidium is the softest, and lithium the 
hardest of these metals. 

In some of their salts a similar gradational relation is observed ; the 
carbonates, for example, of caesium, rubidium, and potassium are highly 
deliquescent, absorbing water greedily from the air, whilst carbonate of 
sodium is not deliquescent, and carbonate of lithium is sparingly soluble 
in water. The difficult solubility of the carbonate and phosphate of lithium 
constitutes the connecting link between this and the succeeding group of 
metals, the carbonates and phosphates of which are insoluble in water. 



BAKIUM. 

Ba" = 137 parts by weight. 

194. Barium, so named from the great weight of its compounds (fiapvs, 
heavy), is found in considerable abundance in the north of England, in 
two minerals known as Witlierite (barium carbonate, BaC0 3 ) and heavy 
spar (barium sulphate, BaS0 4 ). Witherite is found in large masses m 
the lead mines at Alston Moor, and at Anglesark in Lancashire. It is 
said to be used for poisoning rats, and was originally mistaken, on account 
of its great weight, for an ore of lead. 

The metal itself is obtained by decomposing fused barium chloride by 
the galvanic current. It is a pale yellow malleable metal of sp. gr. about 
4, which is easily oxidised by air, and rapidly decomposes water at 
common temperatures. 

Such compounds of barium as are used in the arts are chiefly prepared 
from heavy spar or barium sulphate, which is remarkable for its insolu- 
bility in water and acids. In order to prepare other compounds of barium 
from this refractory mineral, it is ground to powder and strongly heated 
in contact with charcoal or some other carbonaceous substance, which 
removes the oxygen from the mineral in the form of carbonic oxide, 
and converts it into barium sulphide, BaS0 4 + C 4 = 4CO + BaS, This 



BARIUM. 275 

latter compound, being soluble in water, can be readily converted into 
other barytic compounds. 

The artificial barium sulphate, which is used by painters, instead of 
white lead, under the name of permanent white, and is employed for 
glazing cards, is prepared by mixing the solution of barium sulphide with 
dilute sulphuric acid, when the barium sulphate separates as a white 
precipitate, which is collected, washed, and dried — 
BaS + H. 2 S0 4 = H 2 S + BaS0 4 . 

The artificial barium carbonate, which is used in the manufacture of 
some kinds of glass, is prepared by passing carbonic acid gas through a 
solution of barium sulphide, when the carbonate is precipitated; BaS 
+ H 2 + C0 2 = H 2 S + BaC0 3 . 

In preparing compounds of barium from heavy spar on the small scale, it is better 
to convert the sulphate into barium carbonate. 50 grs. of the finely-powdered 
sulphate are mixed with 100 grs. of dried carbonate of soda, 600 grs. of powdered 
nitre, and 100 grs. of very finely powdered charcoal. The mixture is placed on a 
heap upon a brick or iron plate, and kindled with a match, when the heat evolved 
by the combustion of the charcoal in the oxygen of the nitre fuses the barium 
sulphate with the sodium carbonate, when they are decomposed into barium carbonate 
and so'lium sulphate ; BaS0 4 + jSra. 2 C0 3 = Na 2 S0 4 + BaCO :v The fused mass is thrown 
into boiling water, which dissolves the sodium sulphate and leaves the barium 
carbonate. The latter may be allowed to settle, and washed several times, by 
decantation, with distilled water, until the washings no longer yield a precipitate- 
with barium chloride, showing that the whole of the sodium sulphate has been 
washed away and pure barium carbonate remains. 

Barium nitrate, Ba(lST0 3 ) 2 , is obtained by dissolving the carbonate in 
diluted nitric acid, and evaporating the solution, when octahedral crystals 
of the nitrate are deposited. It is an ingredient in some kinds of blasting 
powder used by miners. If barium nitrate be heated in a porcelain crucible, 
it fuses and is decomposed, leaving a grey porous mass of baryta ; * 
Ba(M) 3 ) 2 = BaO + 2M) 2 + O . 

Barium hydrate may be procured by adding 4 oz. of the powdered 
barium nitrate to 12 oz. of a boiling solution of sodium hydrate of sp. gr. 
1T3 (prepared by dissolving 3 oz. of commercial sodium hydrate in 20 
measured ounces of water) ; the solution becomes turbid from the separa- 
tion of barium carbonate produced from the sodium carbonate in the 
hydrate ; it is boiled for some minutes and then filtered ; on partial cooling, 
some crystals of undecomposed barium nitrate are deposited, and if the clear 
liquid be poured off into another vessel and stirred, it deposits abundant 
crystals of barium hydrate having the composition Ba(HO) 9 8Aq. ; these 
effloresce and become opaque when exposed to air, becoming Ba(HO) 9 . Aq. ; 
when heated to redness, they become pure barium hydrate Ba(HO) , which 
fuses, but is not decomposed when further heated. The hydrate is 
moderately soluble in water, the solution being strongly alkaline and 
absorbing carbonic acid gas from the air, depositing barium carbonate. 

When baryta is heated in a tube through which oxygen or air is passed, 
it absorbs the oxygen and is converted into barium dioxide (Ba0 2 ), 
which is employed for the preparation of hydric peroxide (see p. 53). 

Barium chloride, which is the barium compound most commonly 
employed in the laboratory, may be obtained by dissolving the carbonate 
in diluted hydrochloric acid, and evaporating the solution; on cooling, 
the chloride is deposited in tabular crystals, BaCl 2 .2Aq. 

* Containing, according to "Rammelsberg, much barium peroxide. 



276 STRONTIUM— CALCIUM. 

On the large scale, it is generally manufactured by fusing heavy spar 
(barium sulphate) with calcium chloride (the residue from the prepara- 
tion of ammonia, see p. 124) in a reverberatory furnace — 

BaS0 4 + CaCl 2 = CaS0 4 + BaCl 2 . 

The mass is rapidly extracted with hot water, which leaves the calcium 
sulphate undissolved, and the clear solution of barium chloride is decanted 
and evaporated. If the calcium sulphate and barium chloride were 
allowed to remain long together in contact with the water, barium sulphate 
and calcium chloride would be reproduced. 

Barium chlorate, Ba(C10 3 ) 2 , is employed in the manufacture of fire- 
works : , being prepared for that purpose by dissolving the artificial barium 
carbonate in solution of chloric acid ; it forms beautiful shining tabular 
crystals. When mixed with combustible substances, such as charcoal and 
sulphur, it imparts a brilliant green colour to the flame of the burning- 
mixture (see p. 166). 
, All the soluble salts of barium are very poisonous. 

STKOOTIUM. 

Si*" = 87 *5 parts by weight. 

195. Strontium is less abundant than barium, and occurs in nature in 
similar forms of combination. Strontianite, the strontium carbonate 
(SrC0 3 ), was first discovered in the lead mines of Strontian in Argyle- 
shire, and has since been found in small quantity in some mineral waters. 

Celestine (so called from the blue tint of many specimens) is the stron- 
tium sulphate (SrS0 4 ), and is found in beautiful crystals associated with 
the native sulphur in Sicily. It is also met with in this country, and is 
the source from which the strontium nitrate employed in firework com- 
positions is derived. The strontium sulphate resembles barium sulphate 
with respect to its insolubility, and is converted into the soluble strontium 
sulphide (SrS) by calcination with carbonaceous matter. The solution of 
strontium sulphide so obtained is decomposed by nitric acid, and the 
strontium nitrate crystallised from the solution. This salt forms prismatic 
crystals which have the formula Sr(JST0 3 ) 2 .4Aq. It has the property of 
imparting a magnificent crimson colour to flames, and is hence largely 
used for the preparation of red theatrical fire (see p. 165), The other 
compounds of strontium possess too little practical importance, and too 
nearly resemble those of barium, to require particular description here. 

The metal itself is prepared in a similar manner to metallic barium, 
which it much resembles, but is lighter (sp. gr. 2*54). It burns, when 
heated in air, with a crimson flame. 

CALCIUM. 

Ca"r=40 parts by weight. 

196. No other metal is so largely employed in a state of combination 
as calcium, for its oxide, lime (CaO), occupies among bases much the 
same position as that which- sulphuric acid holds among the acids, and is 
used, directly or indirectly, in most of the arts and manufactures. 

Like barium and strontium, it is found, though far more abundantly 
than these, in the mineral kingdom, in the forms of carbonate and sul- 
phate, but it also occurs in large quantity as calcium fluoride (p. 181), 



CARBONATE OF LIME. 277 

and less frequently in the form of phosphate (p. 222). Calcium, more- 
over, is found in all animals and vegetables, and its presence in their food, 
in one form or other, is an essential condition of their existence. 

Metallic calcium may be obtained by decomposing fused calcium iodide 
with metallic sodium. It has a light golden-yellow colour, is harder than 
lead, and very malleable ; it oxidises slowly in air at the ordinary tempera- 
ture, but when heated to redness, it fuses and burns with a very brilliant 
white light, being converted into lime (calx). It decomposes water at 
the ordinary temperature. It is lighter than barium and strontium, its 
specific gravity being 1*58. 

Carbonate of Lime or Calcium Carbonate (CaO.C0 2 or CaC0 3 ), 
from which all the manufactured compounds of lime are derived, consti- 
tutes the different varieties of limestone which are met with in such 
abundance. 

Limestones and chalk are simply calcium carbonate in an amorphous or 
uncrystallised state. The oolite limestone, of which the Bath and Port- 
land building-stones are composed, is so called from its resemblance to the 
roe of a fish (coov, an egg). Marble, in its different varieties, is an assem- 
blage of minute crystalline grains of calcium carbonate, sometimes varie- 
gated by the presence of oxides of iron and manganese, or of bituminous 
matter. This last constituent gives the colour to black marble. Calcium 
carbonate is also found in large transparent rhombohedral crystals, which 
are known to mineralogists as calcareous spar, calc spar, or Iceland spar. 
When the crystals have the form of a six-sided prism, the mineral is 
termed Arragonite. The attention of the crystallographer has long been 
directed to these two crystalline forms of calcium carbonate, on account 
of the circumstance, that if a prism of arragonite be heated, it breaks up 
into a number of minute rhombohedra of calc spar. Satin-spar is a 
variety of calcium carbonate. 

Calcium carbonate is a chief constituent of the shells of fishes and of 
egg-shells, so that, except calcium phosphate, no mineral compound has 
so large a share in the composition of animal frames. Corals also con- 
sist chiefly of calcium carbonate derived from the skeletons of innumer- 
able minute insects. The mineral gaylussite is a double carbonate of 
calcium and sodium (CaC0 3 ,Na 2 C0 3 .5Aq.), and is scarcely affected by 
water unless previously heated, when water dissolves out the sodium 
carbonate. Baryto-calcite is a double carbonate of barium and calcium 
(BaCG 3 ,CaC0 3 ). 

Lime (CaO). — The process by which lime is obtained from the car- 
bonate has been already alluded to under the name of lime-burning. In 
order that the carbonic acid gas may be completely expelled from the car- 
bonate of lime, it is necessary that the products of combustion of the fuel 
should be allowed to pass over the limestone, since, although a very 
intense heat is insufficient to decompose carbonate of lime when shut up 
in a crucible, the decomposition is easily effected if the carbonate be 
heated in a current of atmospheric air or of any other gas, especially if 
aqueous vapour be present, as is the case in the products of combustion 
of the fuel. 

Accordingly, a kiln is commonly employed of the form of an inverted 
cone of brick-work (fig. 236), and into this limestone and fuel are 
thrown in alternate layers. The former, losing its C0 2 before it reaches 
the bottom of the furnace, is raked out in the form of burnt or quick 



278 



SULPHATE OF LIME. 



lime (CaO), whilst its place is supplied by a fresh layer of limestone 
thrown in at the top of the kiln. Fig. 237 represents another form of 
kiln, in which the limestone is supported upon an arch built with large 
lumps of the stone above the fire, which is kept burning for about three 
days and nights, until the whole of the limestone is decomposed. 





Fig. 236.— Lime-kiln. 



Fig. 237.— Lime-kiln. 



The usual test of the quality of the lime thus obtained consists in 
sprinkling it with water, with which it should eagerly combine, evolving 
much heat,* swelling greatly, and crumbling to a light white powder of 
calcium hydrate (slaked lime) Ca(HO) 2 . Lime which behaves in this 
manner is termed fat lime; whereas, if it be found to slake feebly, it is 
pronounced a poor lime, and is known to contain considerable quantities 
of foreign substances, such as silica, alumina, magnesia, &c. Lime is said 
to be overhurnt when it contains hard cinder-like masses of silicate of lime, 
formed by the combination of the silica, which is generally found in 
limestone, with a portion of the lime, under the influence of excessive 
heat in the kiln. 

The calcium hydrate is about twice as soluble in cold as it is in hot 
water, so that lime-water should always be made by shaking slaked lime 
with cold distilled water, which dissolves about 1 '700th of its weight; 
the solution is allowed to settle in a closed bottle, for it absorbs carbonic 
acid gas rapidly from the air. Crystals of calcium hydrate have been 
obtained by evaporating lime-water in vacuo. 

Sulphate of Lime, or Calcium Sulphate, in combination with water 
(CaS0 4 .2H 2 0), is met with in nature, both in the form of transparent 
prisms of selenite, and in opaque and semi-opaque masses known as 
alabaster and gypsum. It is this latter form which yields plaster of 
Paris, for when heated to between 300° and 400° F., it loses about two- 
thirds of its water, becoming 3CaS0 4 .2H 2 0, and if the mass be then 
jjowdered, and again mixed with water, the powder recombines with it 
to form a mass, the hardness of which nearly equals that of the original 
gypsum. 

In the preparation of plaster of Paris, a number of large lumps of 
gypsum are built up into a series of arches, upon which the rest of the 

* The sudden slaking of a large quantity of lime is a common cause of fire. 



CHLORIDE OF CALCIUM. 279 

gypsum is supported ; under these arches the fuel is burnt, and its flame 
is allowed to traverse the gypsum, care being taken that the temperature 
does not rise too high, or the gypsum is overburnt, and does not exhibit 
the property of recombining with water. When the operation is supposed 
to be completed, the lumps are carefully sorted, and those which appear 
to have been properly calcined are ground to a very fine powder. When 
this powder is mixed with water to a cream, and poured into a mould, 
the minute particles of calcium sulphate combine with water to reproduce 
the original gypsum (CaS0 4 .2H 9 0), and this act of combination is 
attended with a slight expansion which forces the plaster into the finest 
lines of the mould. If the setting of plaster of Paris be watched with 
the microscope, the gradual crystallisation may be perceived. The over- 
burnt plaster will not crystallise unless mixed with good plaster, when the 
crystallisation pervades both. An addition of one-tenth of lime to the 
plaster hardens it and acclerates the setting. 

Stucco consists of plaster of Paris (occasionally coloured) mixed with a 
solution of size ; certain cements used for building purposes (Keene's and 
Keating's cements) are prepared from burnt gypsum, which has been 
soaked in a solution of alum and again burnt ; and although the plaster 
thus obtained takes much longer to set than the ordinary kind, it is much 
harder, and therefore takes a good polish. 

Plaster of Paris is much damaged by long exposure to moist air, from 
which it regains a portion of its water, and its property of setting is so far 
diminished. 

Precipitated calcium sulphate is used by paper-makers under the name 
of pearl hardener. 

CaS0 4 forms the mineral anhydrite, a bed. of which, when exposed to 
the air in a railway cutting, has been known to increase in bulk by absorb- 
ing water to such an extent as to disturb the stability of the sides of the 
cutting. 

Calcium chloride (CaCl 2 ) has been mentioned as the residue left in 
the preparation of ammonia. The pure salt may be obtained by dissolving- 
pure calcium carbonate (white marble) in hydrochloric acid, and evaporat- 
ing the solution, when prismatic crystals of the composition CaCl 2 .6Aq. 
are obtained. When these are heated they melt, and at about 390° P. 
are converted into a white porous mass of CaCl 2 .2Aq., which is much 
used for drying gases. At a higher temperature, fused calcium chloride, 
free from water, is left ; this is very useful for removing water from some 
liquids. A saturated solution of calcium chloride boils at 355° F., and 
is sometimes used as a convenient bath for obtaining a temperature above 
the boiling-point of water. In consequence of the attraction of calcium 
chloride for water, surfaces wetted with a solution of the salt never get 
dry. Pope mantlets, for the protection of gunners, are saturated with it 
to prevent their taking fire. 

When calcium hydrate is boiled with a strong solution of calcium 
chloride, it is dissolved, and the filtered solution deposits prismatic crystals 
of calcium oxychloride, CaCl 2 .3Ca0.16Aq., which are decomposed by 
pure water. 

Calcium sulphide (CaS) has lately acquired some importance, on account 
of its presence in Balmain's Luminous Paint., Its property of shining 
in the dark after the exposure to a bright light was observed by Canton 
in 1761 ; his so-called phosphorus was obtained by strongly heating oyster- 



280 ATOMIC HEATS. 

shells with sulphur. The phosphorescence is not due to slow oxidation, 
since a specimen which has been kept for more than a century in a 
sealed tube still exhibits it. 

197. General review of the metals of the alkaline earths. — Barium, 
strontium, and calcium form a highly interesting natural group of metals 
related to each other in a most remarkable manner. They exhibit a 
marked gradation in their attraction for oxygen ; barium is more readily 
tarnished or oxidised, even in dry air, than strontium, and strontium more 
readily than calcium. The hydrates of the metals exhibit a similar 
gradation in properties ; barium hydrate does not lose its water, however 
strongly it may be heated, whereas the hydrates of strontium and calcium 
are decomposed at a red heat. Then barium hydrate and strontium 
hydrate are far more soluble in water than calcium hydrate (which requires 
about 700 parts of water to dissolve it), and all these three exhibit a very 
decided alkaline reaction which entitles them to the name of alkaline earths. 

Among the other compounds of these metals, the sulphates may be 
named as presenting a gradation of a similar description ; for barium 
sulphate may be said to be insoluble in water, strontium sulphate dissolves 
to a very slight extent, and calcium sulphate is rather more soluble. 

The manner in which these metals are associated in nature is also not 
without its significance ; for if two of them are found in the same 
mineral, they will usually be those which stand next to each other in 
the group ; thus strontium carbonate is found together with barium 
carbonate in witherite, whilst calcium carbonate is associated with strontium 
sulphate in celestine. Again, strontium carbonate is often found with 
calcium carbonate in arragonite. 

198. Relation between specific heats and atomic weights — Atomic heats. 
— Since the specific volumes of the vapours of these metals have not been 
ascertained, recourse is had to their specific heats in order to ascertain 
their atomic weights. It will be remembered that the specific heat of 
a substance is the quantity of heat required to raise it 1° in tempera- 
ture, as compared with the quantity of heat required to raise an equal 
weight of water 1°; or, more concisely, the quantity of heat required 
to raise one part by weight of the substance 1° (referred to water as the 
unit). 

Thus, the specific heats of potassium, sodium, and lithium are, respec- 
tively, 0-1696, 0*2934, and 0*9408; these numbers representing the 
relative quantities of heat required to "raise one part by weight of each 
of these metals 1° in temperature, supposing that an equal weight of 
water would be raised 1° by a quantity of heat expressed by one. No 
simple relation can be traced between these numbers, but if the quan- 
tities of heat be calculated which are required to raise atomic weights of 
these elements 1°, the case will be different. 

If 0*1696 be the quantity of heat required to raise one part by weight 
of potassium 1°; 0*1696 x 39, or 6*61, will represent the quantity of heat 
required to raise 39 parts (1 atom) of potassium 1°. In the same way, 
0*2934 x 23, or 6*75, is the quantity of heat required to raise 23 parts 
(1 atom) of sodium 1° ; and 0*9408 x 7, or 6*59, is the quantity required 
to raise 7 parts (1 atom) of lithium 1°. Allowing for experimental error in 
the determination of the specific heats, these numbers, 6*61, 6*75, and 
6*59, may be regarded as representing the same quantities of heat, and 



MAGNESIUM. 281 

they are the atomic heats of these metals, that is, the relative quantities 
of heat required to raise an atom of each 1° in temperature. 

The atomic heat, therefore, which is common to these three metals may 
be represented by the mean of the three numbers, or 6'65. 

The experiments which have been made to determine the specific heats 
of those elements which can be obtained in a similar physical condition, 
lend strong support to the belief that the atomic heats of all elements 
belonging to the same group are identical, and even hold out a prospect 
of the identity of the atomic heats of a great majority of the elementary 
bodies. 

A similar relation has been observed between the atomic heats of com- 
pound bodies belonging to the same group ; thus, if the specific heats of 
the chlorides of potassium, sodium, and lithium be multiplied by the 
atomic weights of those chlorides, the product in each case will approach 
very nearly to the number 12-69. If these chlorides be allowed to con- 
tain one atom of each of their constituents, and it be supposed that the 
atomic heats of these constituents are identical, the half of this number 
(or 6*34) should represent the atomic heat of the alkali-metals, and, in 
fact, it does nearly coincide with that number. 

The specific heats of barium, strontium, and calcium have not been 
determined, and therefore their atomic heats cannot be directly ascer- 
tained. 

The specific heats of the chlorides of barium, strontium, and calcium 
have been ascertained to be represented by the numbers 0*0900, # 1180, 
and 0T686 respectively. Now, the atomic heats of the chlorides, obtained 
by multiplying their atomic weights into their specific heats, would be 
expressed by the mean number 18 "72 ; dividing this by 3, the presumed 
number of atoms in the chloride, we obtain the number 6*24 for the 
atomic heat of each of the elements, which agrees very well with that 
calculated for the alkali-metals. 

MAGNESIUM, 

Mg" = 24-3 parts by weight. 

199. Magnesium is found, like calcium, though less abundantly, in 
each of the three natural kingdoms. Among minerals containing this 
metal, those with which Ave are most familiar are certain combinations of 
silica and magnesia (silicates of magnesia) known by the names of talc, 
steatite or French chalk, asbestos, and meerschaum, which always contains 
water. Magnesite is a carbonate of magnesium. Most of the minerals 
containing magnesium have a remarkably soapy feel. The compounds of 
magnesium, which are employed in medicine, are derived either from the 
mineral dolomite or magnesian limestone which contains the carbonates 
of magnesium and calcium, or from the magnesium sulphate which is 
obtained from sea water and from the waters of many mineral springs. 

Metallic magnesium has acquired some importance during the last few 
years as a source of light. When the extremity of a wire of this metal 
is heated in a flame, it takes fire, and burns with a dazzling white light, 
becoming converted into magnesia (MgO). If the burning wire be plunged 
into a bottle of oxygen, the combustion is still more brilliant. The light 
emitted by burning magnesium is capable of inducing chemical changes 
similar to those caused by sunlight, a circumstance turned to advantage 



282 SULPHATE OF MAGNESIA. 

for the production of photographic pictures by night. Attempts have 
been made to introduce magnesium as an illuminating agent for general 
purposes, but the large quantity of solid magnesia produced in its com- 
bustion forms a very serious obstacle to its use. The metal is extracted 
from magnesium chloride (see p. 118) by fusing it with sodium, using 
sodium chloride and calcium fluoride to promote the fusibility of the 
mass. 

On a small scale, magnesium may be prepared by mixing 900 grs. of magnesium 
chloride with 150 grs. of calcium fluoride, 150 of fused sodium chloride, and 150 of 
sodium cut into slices (see p. 119). The mixture is thrown into a red hot earthen 
crucible, which is then covered again and heated. When the action appears to have 
terminated, the fused mass is stirred with an iron rod to promote the union of the 
globules of magnesium. It is then poured upon an iron tray, allowed to solidify, 
broken up, and the globules of magnesium separated from the slag ; they may be 
collected into one globule by throwing them into a melted mixture of chlorides of 
magnesium and sodium and fluoride of calcium. 

In most of its physical and chemical characters, magnesium resembles 
zinc, though its colour more nearly approaches that of silver ; in ductility 
and malleability it also surpasses zinc. It is nearly as light, however, 
as calcium, its specific gravity being 1*74. It fuses below a red heat, 
and may be distilled like zinc. Cold water has scarcely any action 
upon magnesium ; even when boiled it oxidises the metal very slowly. 
In the presence of acids, however, it is rapidy oxidised by water. 
Solution of ammonium chloride also dissolves it, owing to the tendency 
of the magnesium salts to form double salts with those of ammonium ; 
4NH 4 Cl + Mg = (^ T H 4 ) 2 MgCl 4 + H 2 + 2NH 3 . Magnesium is one of the 
few elements which unite directly with nitrogen at a high temperature. 
The magnesium nitride, Mg 3 N 2 , has been obtained in transparent crystals, 
and is evidently composed alter the type 2NH 3 , so that it is not surprising 
that the action of water upon it gives rise to magnesia and ammonia; 
Mg 3 N 2 + 3H 2 = 2NH 3 + 3MgO. 

If a foot of magnesium tape be burnt in air, the residue evolves much 
ammonia when boiled with water. 

The sulphate of magnesia or magnesium sulphate, so well known as 
Epsom salts, is sometimes prepared by calcining dolomite to expel the 
carbonic acid gas, washing the residual mixture of lime and magnesia 
with water to remove part of the lime, and treating it with sulphuric 
acid, which converts the calcium and magnesium into sulphates ; and since 
calcium sulphate is almost insoluble in water, it is readily separated from 
the magnesium sulphate which passes into the solution, and is obtained by 
evaporation in prismatic crystals, having the composition MgS0 4 H 2 0. 6Aq. 
The preparation of Epsom salts from sea water has already been alluded 
to (p. 261). In some parts of Spain magnesium sulphate is found in 
large quantities (like nitre in hot climates) as an efflorescence upon the 
surface of the soil. This sulphate, as well as that contained in well-waters, 
appears to have been produced by the action of the calcium sulphate, 
originally present in the water, upon magnesian limestone rocks ; 
MgC0 3 + CaS0 4 = MgS0 4 + CaC0 3 . 

The water of constitution in the magnesium sulphate may be displaced 
by the sulphate of an alkali-metal without alteration in its crystalline form; 
a double sulphate of magnesium and potassium (MgS0 4 .I\ 2 S0 4 6Aq.), 
and a similar salt of ammonium may be thus obtained. The mineral 
polyhalite (ttoAv's, many, aA?, salt) is a remarkable salt, containing 



CHLORIDE OF MAGNESIUM. 283 

MgS0 4 .K 2 S0 4 2CaS0 4 ,2H 2 0.* Water decomposes it into its constituent 
salts. 

The preparation commonly used in medicine under the name of mag- 
nesia, is really a basic magnesium carbonate, or a compound of magnesium 
carbonate with magnesium hydrate and water, in the porportions expressed 
by the formula, 5MgC0 3 .2Mg(HO) 2 .7Aq. It is obtained by mixing boil- 
ing solutions of magnesium sulphate and sodium carbonate, when one- 
fourth of the carbon dioxide is expelled in the state of gas ; the white 
precipitate is thrown upon a cloth strainer, well washed, and dried in 
rectangular moulds. 

Another process for preparing magnesium carbonate consists in heating 
magnesian limestone to low redness, so as to decompose the magnesium 
carbonate which it contains, and exposing it, under pressure, to the action 
of water and carbonic acid, which dissolves the magnesia and leaves the 
calcium carbonate. On boiling the solution, to expel the excess of car- 
bonic acid gas, the magnesium carbonate is precipitated. 

By moderately heating the carbonate, its water and carbonic acid gas 
are expelled, and pure or calcined magnesia (MgO) is left, which is very 
slightly soluble in water and feebly alkaline. 

The mineral periclase consists of magnesia in a crystallised form. Mag- 
nesia combines with water to form a hydrate, Mg(HO) 2 , but not with 
evolution of heat, as in the cases of baryta, strontia, and lime. Crys- 
tallised magnesium hydrate constitutes the mineral brucite. Magnesia, 
like lime, is remarkable for its infusibility. 

It has recently been noticed that calcined magnesia, when mixed with 
water, solidifies after a time into a very hard, compact mass of magnesium 
hydrate, and may serve, like plaster of Paris, for taking casts. Dolomite 
calcined below redness also sets to a very hard mass with water. 

The magnesium orthophosphate, Mg 3 (P0 4 ) 2 enters into the composi- 
tion of bones, and the phosphate of magnesium and ammonium, or triple 
phosphate (MgNH 4 HP0 4 ), is found in calculi and in the minerals guanite 
and siruvite. 

Magnesium borate composes the mineral boracite; hydroboracite is a 
hydrated borate of calcium and magnesium. 

Serpentine and olivine are silicates of magnesia and ferrous oxide. 
Some of the varieties of serpentine are employed for preparing the com- 
pounds of magnesium, for they are easily decomposed by acids with 
separation of silica. 

Pearl spar is a crystallised carbonate of calcium and magnesium. 

Magnesium chloride is important as the source of metallic magnesium. 
It is easily obtained in solution by neutralising hydrochloric acid with 
magnesia or its carbonate, but if this solution be evaporated in order to 
obtain the dry chloride, a considerable quantity of the salt is decomposed 
by the water at the close of the evaporation, leaving much magnesia 
mixed with the chloride (MgCl 2 + H 2 = 2HC1 + MgO). This decomposi- 
tion may be prevented by mixing the solution with three parts of 
chloride of ammonium for every part of magnesia, when a double salt, 
MgCl 2 . 2^11401, is formed, which may be evaporated to dryness without 
decomposition, and leaves fused magnesium chloride when further heated, 
the ammonium chloride being volatilised. The magnesium chloride 

* Polyhalite and hieserite, MgS0 4 ,H.,0, are found in the salt-beds of Stassfurth. Kainite, 
from the same locality, is K 2 S0 4 .MgS0 4 .MgClo.6Aq. 



284 zinc. 

absoibs moisture very rapidly from the air, and is very soluble in water. 
Like all the soluble salts of magnesium, it has a decidedly bitter taste. 
When magnesia is moistened with a strong solution of magnesium 
chloride, it sets into a hard mass like plaster of Paris, apparently from the 
formation of an oxy chloride, MgO.MgCl 2 . It may be mixed with several 
times its weight of sand, and will bind it firmly together. 

ZINC. 

Zu" = 65 parts by weight. 

200. Zinc occupies a high position among useful metals, being peculiarly 
fitted, on account of its lightness, for the construction of gutters, water- 
pipes, and roofs of buildings, and possessing for these purposes a great 
advantage over lead, since the specific gravity of the latter metal is about 
11 *5, whilst that of zinc is only 6*9. For such applications as these, 
where great strength is not required, zinc is preferable to iron, on account 
of its superior malleability ; for although a bar of zinc breaks under 
the hammer at the ordinary temperature, it becomes so malleable at 
250° F. as to admit of being rolled into thin sheets. This malleability 
of zinc when heated was discovered only in the commencement of this 
century, until which time the only use of the metal was in the manufac- 
ture of brass. When zinc is heated to 400° F., it again becomes brittle. 
The easy fusibility of zinc also gives it a great advantage over iron, as 
rendering it easy to be cast into any desired form; indeed, zinc is 
surpassed in fusibility (among the metals in ordinary use) only by tin 
and lead, its melting-point being below a red heat, and usually estimated 
at 770° F. Zinc is also less liable than iron to corrosion under the 
influence of moist air, for although a bright surface of zinc soon 
tarnishes when exposed to the air, it merely becomes covered with a thin 
film of zinc oxide (passing gradually into basic carbonate, by absorp- 
tion of carbonic acid from the air) wdiich protects the metal from further 
action. 

The great strength of iron has been ingeniously combined with the 
durability of zinc, in the so-called galvanised iron, which is made by coat- 
ing clean iron with melted zinc, thus affording a protection much needed 
in and around large towns, where the sulphurous and sulphuric acids 
arising from the combustion of coal, and the acid emanations from 
various factories, greatly accelerate the corrosion of unprotected iron. 
The iron plates to be coated are first thoroughly cleansed by a process 
which will be more particularly noticed in the manufacture of tin-plate, 
and are then dipped into a vessel of melted zinc, the surface of wdiich is 
coated with sal ammoniac (ammonium chloride) in order to dissolve the 
zinc oxide which forms upon the surface of the melted metal, and might 
adhere to the iron plate so as to prevent its becoming uniformly coated 
with the zinc* A more firmly adherent coating of zinc is obtained by 
first depositing a thin film of tin upon the surface of the iron plate by 
galvanic action, and hence the name galvanised iron. 

The ores of zinc are found pretty abundantly in England, chiefly in 
the Mendip Hills in Somersetshire, at Alston Moor in Cumberland, in 

* The sal ammoniac acts upon the heated zinc according to the equation, Zn + 2NH 4 C1 
= ZnC] 2 +2NH 3 -|-H 2 , and the zinc chloride which is formed dissolves the oxide from the 
surface of the metal, producing zinc oxychloride. 



EXTRACTION OF ZINC. 285 

Cornwall, and Derbyshire, bnt the greater part of the zinc used in this 
country is imported from Belgium and Germany, being derived from the 
ores of Transylvania, Hungary, and Silesia. 

Metallic zinc is never met with in nature. Its chief ores are calamine 
or zinc carbonate (ZnC0 3 ), blende or zinc sulphide (ZnS), and red zinc ore, 
in which zinc oxide (ZnO) is associated with the oxides of iron and 
manganese. 

Calamine is so called from its tendency to form masses resembling a 
bundle of reeds (calamus, a reed). It is found in considerable quantities 
in Somersetshire, Cumberland, and Derbyshire. A compound of car- 
bonate with hydrate of zinc, ZnC0 3 .2Zn(HO) 2 , is found abundantly in 
Spain. The mineral known as electric calamine is a silicate of zinc 
(2ZnO.Si0 9 .H 2 0). Blende derives its name from the German blenden, 
to dazzle, in allusion to the brilliancy of its crystals, which are gene- 
rally almost black from the presence of iron sulphide, the true colour of 
pure zinc sulphide being white. Blende is found in Cornwall, Cumber- 
land, Derbyshire, Wales, and the Isle of Man, and is generally associated 
with galena or lead sulphide, which is always carefully picked out of the 
ore before smelting it, since it would become converted into lead oxide, 
which corrodes the earthen crucibles employed in the process. 

In England the extraction of zinc from its ores is carried on chiefly at 
Swansea, Birmingham, and Sheffield. Before extracting the metal from 
these ores, they are subjected to a preliminary treatment which brings 
them both to the condition of zinc oxide. For this purpose the calamine 
is simply calcined in a reverberatory furnace, in order to expel carbonic 
acid gas ; but the blende is roasted for ten or twelve hours, with constant 
stirring, so as to expose fresh surfaces to the air, when the sulphur passes 
off in the form of sulphurous acid gas, and its place is taken by the 
oxygen, the ZnS becoming ZnO. The extraction of the metal from this 
zinc oxide depends upon the circumstance that zinc is capable of being 
distilled at a bright red heat, its boiling-point being 1904° F. 

The facility with which this metal passes off in the form of vapour is 
seen when it is melted in a ladle over a brisk fire, for at a bright red 
heat abundance of vapour rises from it, which, taking fire in the air, 
burns with a brilliant greenish-white light, throwing off into the air 
numerous white flakes of light zinc oxide (the philosopher's wool, or nil 
album of the old chemists). 

The distillation of zinc may be effected on the small scale in a black-lead crucible 
(A, fig. 238) about 5 inches high and 3 in diameter. A hole is drilled through the 
bottom with a round file, and into this is fitted a piece of wrought-iron gas-pipe (B) 
about 9 inches long and 1 inch wide, so as to reach nearly to the top of the inside of 
the crucible. Any crevices between the pipe and the sides of the hole are carefully 
stopped up with fireclay moistened with solution of borax. A few ounces of zinc 
are introduced into the crucible, the cover of which is then carefully cemented on 
with fireclay (a little borax being added to bind it together at a high temperature), 
and the hole in the cover is stopped up with fireclay. The crucible having been 
kept for several hours in a warm place, so that the clay may dry, it is placed in a 
cylindrical furnace with a hole at the bottom, through which the iron pipe may pass, 
and a lateral opening into which is inserted an iron tube (C) connected with a forge 
bellows. Some lighted charcoal is thrown into the furnace, and when this has been 
blown into a blaze, the furnace is filled up with coke broken into small pieces. The 
fire is then blown till the zinc distils freely into a vessel of water placed lor its recep- 
tion. Four ounces of zinc may be easily distilled in half an hour. 

English method of extracting zinc. — The zinc oxide, obtained as above 



286 



EXTRACTION OF ZINC FROM ITS ORES. 



from calamine or blende, is mixed with about half its weight of coke or 
anthracite coal. This mixture is introduced into large crucibles (fig. 239) 
with a hole in the bottom through which passes a short wide iron pipe 
destined for the passage of the vapour of zinc. These crucibles are 
about 4 feet high by 2 \ feet wide. Some large pieces of coke are first 
introduced into them to prevent the charge from passing into the iron 
pipes, and when they have been charged with the above mixture, their 
covers are cemented on, and they are heated in furnaces somewhat 
resembling those of a glass-house, each furnace receiving six crucibles, 
which generally contain, in all, one ton of roasted ore. When the mixture 
in the crucibles is heated to redness, it begins to evolve carbonic oxide 




Fig. 238.— Distillation of zinc. 




English zinc furnace. 



produced by the combination of the carbon with the oxygen from the zinc 
oxide. This gas burns with a blue flame at the mouth of the iron pipe; 
but at a bright red heat the metallic zinc which has been thus liberated 
is converted into vapour, and the greenish-white name of burning zinc is 
perceived at the orifice. When this is the case, about 8 feet of iron pipe 
are joined on to the short piece, in order to condense the vapour of zinc, 
which falls into a vessel placed for its reception. The distillation occupies 
about sixty hours, and the average yield is about 35 parts of zinc from 
100 of ore, a considerable quantity of zinc being left behind in the form 
of zinc silicate (electric calamine), which is reduced with difficulty by 
distillation with carbon. 

The zinc thus obtained, however, is mixed with a considerable quantity 
of zinc oxide, and with other foreign matters carried over from the 
crucibles. It is, therefore, again melted in a large iron pan, and allowed 
to rest, in order that the dross may rise to the surface ; this is skimmed 
off, to be worked over again in a fresh operation, and the metal is cast 
into ingots, which are sent into commerce under the name of spelter. 

Belgian process for the extraction of zinc. — At the Vieilie-Montagne 
works, near Liege, calamine is exposed to the rain for several months in 
order to wash out the clay ; it is then calcined to expel the water and 
carbonic acid gas, the zinc oxide so obtained being mixed with half its 



EXTRACTION OF ZINC IN SILESIA. 



287 




Fig. 240.— Belgian 
zinc furnace. 



weight of coal dust, and distilled in fireclay cylinders (C, fig. 240), 

holding about 40 lbs. each, and set in seven tiers of six each in the 

same furnace, the vapour of zinc being conveyed by 

a short conical iron pipe (B) into a eonical iron 

receiver (D), which is emptied every two hours into 

a large ladle, from which the zinc is poured into 

ingot moulds. Each distillation occupies about twelve 

hours. The advantage of this particular mode of 

arranging the cylinders is, that it economises fuel by 

allowing the poorer ores, which require less heat to 

distil all the zinc from them, to be introduced into 

the upper rows of cylinders farthest from the fire (A). 

There are two varieties of Belgian ore, one containing 

33 and the other 46 per cent, of zinc, but a large 

proportion of this is in the form of silicate, which is 

not extracted by the distillation. 

Silesian process for extracting zinc. — In Silesia the 

zinc oxide obtained by the calcination of calamine is 

mixed with fine cinders, and distilled in arched earthen retorts (A, fig. 

241), into which the charge is introduced through a small door (B), which 

is then cemented up. The 

retorts are arranged in a - A 

double row in the same 
furnace (fig. 242), and the 

vapour of zinc is con- 
densed in a bent earthen- 
ware pipe attached to each 
retort, and having an opening (C) near the bend, which is kept closed, 
unless it is necessary to clear out the pipe. In regard to the consumption 
of fuel, this process is far 
more economical than 
that followed in this 
country. The Silesian 
zinc is remelted, before 
casting into ingots, in 
clay instead of iron pots, 
since melted zinc always 
dissolves iron, and a very 
small quantity of that 
metal is found to injure 
zinc when required for 
rolling into sheets. Fi g- 242.— Silesian zinc furnace. 

A small quantity of lead always distils over together with the zinc, 
and since this metal also interferes with the rolling of zinc into sheets, a 
portion of it is separated from zinc intended for this purpose, by melting 
the spelter, in large quantity, upon the hearth of a reverberatory furnace, 
the bed of which is inclined so as to form a deep cavity at the end nearest 
the chimney. The specific gravity of lead being 11*4, whilst that of 
zinc is 6 "9, the former accumulates chiefly at the bottom of the cavity, 
and the ingots cast from the upper part of the melted zinc will contain 
but little lead, since zinc is not able to dissolve more than 1*2 per cent, 
of that metal. 





" 



288 COMPOUNDS OF ZINC. 

Ingots of zinc, when broken across, exhibit a beautiful crystalline frac- 
ture, which, taken in conjunction with the bluish colour of the metal, 
enables it to be easily identified. 

The spelter of commerce is liable to contain lead, iron, tin, antimony, 
arsenic, copper, cadmium, magnesium, and aluminium. Belgian zinc is 
usually purer than the English metal. 

Zinc being easily dissolved by diluted acids, it is necessary to be care- 
ful in employing this metal for culinary purposes, since its soluble salts 
are poisonous. 

It will be remembered that the action of diluted sulphuric acid upon 
zinc is employed for the preparation of hydrogen. Pure zinc, however, 
evolves hydrogen very slowly, since it becomes covered with a number of 
hydrogen bubbles which protect it from further action; but if a piece of 
copper or platinum be made to touch the zinc beneath the acid, these 
metals, being electro-negative towards the zinc, will attract the electro- 
positive hydrogen, leaving the zinc free from bubbles and exposed on all 
points to the action of the acid, so that a continuous disengagement of 
hydrogen is maintained. As a curious illustration of this, a thin sheet of 
platinum or silver foil may be shown to sink in diluted sulphuric acid, 
until it comes in contact with a piece of zinc, when the bubbles of hydro- 
gen bring it up to the surface. The lead, iron, &c, met with in commer- 
cial zinc, are electro-negative to the zinc, and thus serve to maintain a 
constant evolution of hydrogen. 

A coating of metallic zinc may be deposited upon copper by slow galvanic 
action, if the copper be immersed in a concentrated solution of potash, at 
the boiling-point of water, in contact with metallic zinc, when a portion of 
the latter is dissolved in the form of oxide, with evolution of hydrogen, 
and is afterwards precipitated on the surface of the electro-negative copper. 
Zinc oxide (ZnO). — Zinc forms but one oxide, which is known in 
commerce as zinc-white or Chinese white, and is prepared by allowing the 
vapour of the metal to burn in earthen chambers through which a current 
of air is maintained. This zinc-white is sometimes used for painting 
in place of white lead (lead carbonate), over which it has the 
advantages of not injuring the health of the persons using it, and of 
being unaffected by sulphuretted hydrogen, an important consideration 
in manufacturing towns where that substance is so abundantly supplied 
to the atmosphere. Unfortunately, however, the zinc oxide does not 
combine with the oil of the paint as lead oxide does, and the paint 
is consequently more liable to peel off. The zinc oxide has the charac- 
teristic property of becoming yellow when heated, and white again as 
it cools. It is sometimes used in the manufacture" of glass for optical 
purposes. 

Zinc oxide forms a soluble compound with potash, in this respect 
resembling alumina, and therefore metallic zinc, like aluminium, is dis- 
solved by boiling with solution of potash, hydrogen being disengaged 
from the water, the oxygen of which combines with the zinc. 

Zinc sulphate or white vitriol, which is employed in medicine, and more 
extensively in calico-printing, is prepared by roasting blende (zinc sulphide, 
ZnS) at a low temperature, when it combines with oxygen to form ZnS0 4 . 
After roasting, the mass is treated with water, which dissolves the sulphate, 
and yields it again, on evaporation, in prismatic crystals having the 
formula ZnS0 4 H 2 0.6Aq. 



CADMIUM — GLUCINUM. 289 

Zinc phosphate, combined with water, composes the mineral 'hopeite, 
Zn 3 (P0 4 ) 2 .4Aq. 

Zinc chloride (ZnCl 2 ), prepared by dissolving zinc in hydrochloric acid, 
is known in commerce as Burnett's disinfecting fluid, since it is capable 
of absorbing hydrosulphuric acid, ammonia, and other offensive products 
of putrefaction, and arrests the decomposition of wood and animal 
substances. By evaporating its solution, the zinc chloride is obtained in 
a fused state, and solidifies on cooling into white deliquescent masses. It 
has a very powerful attraction for water. 

Zinc chloride is sometimes made from pyrites containing blende. This 
is burnt as usual to furnish S0 2 for the manufacture of sulphuric acid, 
when the ZnS is converted into ZnS0 4 which is extracted from the spent 
pyrites by water, and decomposed with sodium chloride, when Na 2 S0 4 
is deposited in crystals, leaving ZnCl 2 in solution. 

When zinc oxide is moistened with a strong solution of zinc chloride, 
an oxychloride is formed, which soon sets into a hard mass, forming a very 
useful stopping for teeth. 

CADMIUM. 

Cd" = 112 parts by weight. 

201. This metal is found in small quantities in the ores of zinc, its 
presence being indicated during the extraction of that metal (page 286) 
by the appearance of a brown flame (brown blaze) at the commencement 
of the distillation, before the characteristic zinc flame is seen at the orifice 
of the iron tube. Cadmium is more easily vaporised than zinc, boiling 
at 1580° F., so that the bulk of it is found in the first portions of the 
distilled metal. If the mixture of cadmium and zinc be dissolved 
in diluted sulphuric acid, and the solution treated with hydrosulphuric 
acid gas, a bright yellow precipitate of cadmium sulphide (CdS) is 
obtained, which is employed in painting under the name of cadmia. 
By dissolving this in strong hydrochloric acid and adding ammonium 
carbonate, cadmium carbonate (CdC0 3 ) is precipitated, from which 
metallic cadmium may be extracted by distillation with charcoal. 

Although resembling zinc in its volatility and its chemical relations, in 
appearance it is much more similar to tin, and emits a crackling sound 
like that metal when bent. Like tin, also, it is malleable and ductile at 
the ordinary temperature, and becomes brittle at about 180° F. It is as 
fusible as tin, becoming liquid at 442° F., so that it is useful for making 
fusible alloys. An alloy of 3 parts of cadmium with 16 of bismuth, 8 
of lead, and 4 of tin, fuses at 140° F. In its behaviour with acids and 
alkalies cadmium is similar to zinc, but the metal is easily distinguished 
from all others by its yielding a characteristic chestnut-brown oxide 
when heated in air. This oxide (CdO) is the only oxide of cadmium. 

Cadmium iodide (Cdl 2 ), obtained by the action of iodine upon the 
metal in the presence of water, is employed in photography. 

GLUCINUM. 

Gl" = 9'2 parts by weight. 

202. This comparatively rare metal (which derives its name from the sweet taste of 
its salts, jXvkvs, sweet) is found associated with silica and alumina in the emerald, 
which is a double silicate of alumina and glucina, Al 2 3 .3Si0 2 ,3(G10.Si0 2 ), and 
appears to owe its colour to the presence of a minute quantity of oxide of chromium. 

T 



290 ALUMINIUM. 

The more common mineral beryl has a similar composition, but is of a paler green 
colour, apparently caused by iron. Chrysobcryl consists of glucina and alumina, 
also coloured by iron. The earlier analysts of these minerals mistook the glucina 
for alumina, which it resembles in forming a gelatinous precipitate on adding ammonia 
to its solutions, but it is a stronger base than alumina, and is therefore capable of 
displacing ammonia from its salts, and of being dissolved by them. Ammonium 
carbonate is employed to separate the glucina from alumina, since it dissolves the 
glucina in the cold, forming a double carbonate of glucinum and ammonium, from 
which the glucinum carbonate is precipitated on boiling. Glucina (GIO) is inter- 
mediate in properties between alumina and magnesia, resembling the latter in its 
tendency to absorb carbonic acid from the air, and to form soluble double salts with 
the salts of ammonium, and so much resembling alumina in the gelatinous form of 
its hydrate, its solubility in alkalies, and the sweet astringent taste of its salts, that 
it was formerly regarded as a sesquioxide like alumina. 
The metal itself is very similar to aluminium. 

ALUMINIUM. 

Al"' = 27 parts by weight. 

203. Aluminium is the representative of the class of metals usually 
styled metals of the earths proper, and including also glucinum, thorinum, 
yttrium, zirconium, erbium, terbium, cerium, lanthanium, and didymium, 
hut of these aluminium is the only metal having any claim to our atten- 
tion on the ground of its practical importance. 

Aluminium is distinguished among metals, as silicon is among non- 
metallic bodies, for its immense abundance in the solid mineral portion 
of the earth, to which, indeed, it is almost entirely confined, for it is 
present in vegetables and animals in so small quantity that it can scarcely 
be regarded as forming one of their necessary components. Church has, 
however, recently found it in certain cryptogamous plants, especially in 
the Lycopodiums ; the ash of Lycopodium alpinum yielding one-third of 
its weight of alumina. 

One of the oldest rocks, which appears to have originally formed the 
basis of the solid structure of the globe, is that known as granite. This 
mineral, which derives its name from its conspicuous granular structure, 
is a mixture, in variable proportions, of quartz, felspar, and mica, tinged 
of various colours by the presence of small quantities of the oxides of- 
iron and manganese. 

Quartz, which forms the translucent or transparent grains in the granite, 
consists simply of silica; felspar, the dull cream-coloured opaque part, 
is a combination of silica with oxides of aluminium and potassium, its 
composition being represented by the formula K 2 0.3Si0 2 ,Al 2 3 .3Si0 2 . _ 

Mica, so named from the glittering scales which it forms in the granite, 
is also a double silicate of alumina and potash, but the alumina is very 
frequently displaced by ferric oxide, and the potash by magnesia. 

By the long-continued action of air and water, the granite rock is 
gradually crumbled down or disintegrated, an effect which must be 
ascribed to a concurrence of mechanical and chemical causes. Mechani- 
cally, the rock is continually worn down by variations of temperature, 
by the congelation of water within its minute pores, the rock being 
gradually split by the expansion attendant upon such congelation. 
Chemically, the action of water containing carbonic acid would tend to 
remove the potash from the felspar and mica in the form of carbonate of 
potash, whilst the silicate of alumina and the quartz would subsequently 
be separated by the action of water; the former, being so much lighter, 



COMPOSITION OF CLAY, 



291 



would be soon washed away from the heavy quartz, aud when again 
deposited, would constitute clay. 

Although clay, therefore, always consists mainly of silicate of alumina, 
it generally contains some uncombined silicic acid, together with variable 
quantities of lime, of oxide of iron, &c, which give rise to the numerous 
varieties of clay. 

Composition of Clay. 





Chinese Kaolin. 


Fireclay. 
(Stourbridge.) 


1 
Pipeclay. 


Silica, .... 

Alumina, .... 

Water, .... 

Oxide of iron, . 

Lime, .... 

Magnesia, 

Potash, ) 

Soda, \ 


50-5 
337 
11-2 

1-8 

0-8 
1-9 


64-1 
23 1 

10-0 
1-8 

0-9 


537 
32-0 
12-1 

1-4 
0-4 


99 "9 


99-9 99-6 



The silicate of alumina also constitutes the chief portion of several 
other very important mineral substances, among which may be mentioned 
slate, fullers earth, and pumice-stone. Marl is clay containing a consider- 
able quantity of carbonate of lime. Loam is also an impure variety of 
clay. The different varieties of ochre, as well as umber and sienna, are 
simply clays coloured by the oxides of iron and manganese. 

Alum, which is the chief compound of aluminium employed in the arts, 
is always obtained either from clay or slate, but there are several processes 
by which it may be manufactured. 

The simplest process is that in which pipeclay, or some other clay con- 
taining very little iron, is calcined, ground to powder, and heated on the 
hearth of a reverberatory furnace with half its weight of sulphuric acid, 
until it becomes a stiff paste, which is then exposed to air for several 
weeks. During this time the alumina of the clay is acted on by the 
sulphuric acid to form aluminium sulphate, which may be obtained by 
washing the mass with water, when the sulphate dissolves, and the 
undissolved silica (still retaining a portion of the alumina) is left. When 
the solution containing the aluminium sulphate is evaporated to a syrupy 
consistence and allowed to cool, it solidifies into a white crystalline mass, 
which is used by dyers under the erroneous name of concentrated alum, 
or cake-alum, and contains about 47*5 per cent, of the dry salt. The 
alumiaium sulphate can be obtained in crystals containing Al 9 3S0 4 .18Aq.,* 
but there is considerable difficulty in obtaining these crystals on account 
of the extreme solubility of the salt. It is on account of this circumstance 
that the aluminium sulphate is usually converted into alum, which admits 
of very easy crystallisation and purification. In order to transform the 
sulphate into alum, its solution is mixed with potassium sulphate, when, 
by suitable evaporation, beautiful octahedral crystals are obtained, having 
the composition AlK(S0 4 ) 9 .12Aq. 

Alum is more commonly prepared from the mineral termed alum shale, 

* The mineral alunogen found in Xew South Wales has this composition (Liversidge). 
It forms fibrous masses like satin-spar, and occurs in sandstone rocks. 



292 MANUFACTURE OF ALUM. 

which contains silicate of alumina, together with a considerable quantity 
of finely divided iron pyrites and some bituminous matter. This shale 
is coarsely broken up, and built into long pyramidal heaps, together with 
alternate layers of coal, unless the shale should happen to contain a suffi- 
cient amount of bitumen. These heaps are set fire to in several places, 
and are partly smothered with spent ore in order to prevent too great a 
rise of temperature. During this slow roasting of the heap, the iron 
pyrites (FeS 2 ) loses half its sulphur, which is converted by burning into 
sulphurous acid gas (S0 2 ), and this, in contact with the porous shale and 
the atmospheric oxygen, becomes converted into S0 3 (p. 202). This 
latter combines with the alumina to produce sulphate of alumina. The 
roasted heap is then allowed to remain for some months exposed to the 
air, and moistened from time to time, in order to promote the absorption 
of oxygen by the sulphide of iron (FeS), and its conversion into sulphate 
of iron (FeS0 4 ). The heap is afterwards lixiviated with water, which 
dissolves out the sulphates of aluminium and iron, together with some 
magnesium sulphate, which has also been formed in the process. "When 
this crude alum liquor is evaporated to a certain extent, a large quantity 
of ferrous sulphate (green vitriol) crystallises out, and the liquid from 
which these crystals have separated is then mixed with so much solu- 
tion of potassium chloride as a preliminary experiment has shown to be 
necessary to yield the largest amount of alum. The potassium chloride 
is obtained as soap-boiler's waste, and as the refuse from saltpetre refineries 
and glass-houses. The ferrous sulphate still left in the solution is decom- 
posed by the potassium chloride, yielding ferrous chloride, and potassium 
sulphate, which combines which the aluminium sulphate to form alum. 
If there be much magnesium sulphate in the liquor, it is subsequently 
obtained in crystals and sent into the market. 

Where ammonium sulphate can be obtained at a cheap rate (as in 
the neighbourhood of the gas-works), it is very commonly substituted 
for the potassium chloride, when ammonia-alum is obtained instead of 
potash-alum. The former is similar in ali respects to the latter salt, except 
that it contains the hypothetical metal ammonium (NH 4 ) in place of potas- 
sium, and its formula is, therefore, AlNH 4 (S0 4 ) 2 .12Aq. 

For all the uses of alum, in dyeing and calico-printing, in paper-making, 
and in the manufacture of colours, ammonia-alum answers quite as well 
as potash-alum, and hence both these salts are sold under the common 
name of alum. 

These alums are the representatives of an important class of double - 
sulphates, containing a monatomic and a triatomic metal. They all con- 
tain 12 molecules of water of crystallisation, and their crystalline form is 
that of the cube or octahedron. 

The solution of alum is acid to test-papers. When solution of sodium 
carbonate is added to it by degrees, a precipitate of aluminium hydrate is 
formed, which, at first, is redissolved on stirring. The solution to which 
sodium carbonate has been added as long as the precipitate re-dissolves, 
is used under the name of basic alum in dyeing, because stuffs immersed in 
it become impregnated with alumina, which serves as a mordant to attract 
and fix the colouring-matter when the stuff is transferred to a dye-bath. 

Aluminium sulphate is superseding alum in many applications ; being 
prepared by treating clay or Bauxite (see p. 294) with sulphuric acid, and 
precipitating the iron either as ferric arsenite or as Prussian blue. 



ALUMINIUM. = 293 

Alumina. — When ammonia- alum is strongly heated, it leaves a white 
insoluble earthy substance which is alumina itself (A1 9 3 ), and differs 
widely from the metallic oxides which . have been hitherto considered, 
by the feebly basic character which it exhibits.* Kot only is alumina 
destitute of alkaline properties, but it is not even capable of entirely 
neutralising the acids, and hence both aluminium sulphate and alum are 
exceedingly acid salts. 

Pure crystallised alumina is found in nature as the mineral corundum, 
distinguished by its extreme hardness, in which it ranks next to the 
diamond. An opaque and impure variety of corundum constitutes the 
very useful substance emery. The ruby and sapphirej consist of nearly 
pure alumina ; spinelle is a compound of magnesia with alumina, 
MgO.Al 2 3 ; whilst in the topaz the alumina is associated with silica and 
aluminium fluoride. The mineral diaspore is a hydrate of alumina 
(A1 2 3 .2H 2 0), so named from its falling to powder when heated (Staa-Tropa, 
dispersion). 

The artificially prepared aluminium hydrate is characterised by its gelatinous 
appearance. If a little alum be dissolved in warm water, and some ammonia added to 
the solution, the ammonia will combine with the sulphuric acid, whilst the alumina 
will unite with water to form a semi-transparent gelatinous mass of hydrate of 
alumina ; A1 2 3 .3H 2 or Al 2 (HO) 6 . When washed and dried it shrinks very much, 
and forms a mass resembling gum. The hydrate has a grsat attraction for most 
colouring matters, with which it forms insoluble compounds called lakes. Thus, if 
a solution of alum be mixed with infusion of logicood, and a little ammonia added, 
the aluminium hydrate will form, with the colouring matter, a purplish-red lake, 
which may be filtered off, leaving the solution colourless. This property is turned 
to advantage in calico-printing, where the compounds of alumina are largely used as 
mordants. 

Aluminium chloride. — If the alumina obtained by calcining ammonia- 
alum be intimately mixed with charcoal, and strongly heated in an earthen 
tube or retort through which a stream of well-dried chlorine is passed, 
the oxygen- of the alumina is abstracted by the charcoal, to form car- 
bonic oxide, whilst the chlorine combines with the aluminium, yielding 
aluminium chloride (A1 2 C1 6 ) which passes off in vapour, and may be 
condensed^ in an appropriate receiver, as a white crystalline solid — 

A1 2 3 + C 3 + Cl 6 = A1 2 C1 6 + 3CO. 

This formation of aluminium chloride is possessed of some interest, as 
an example of the decomposition of a compound body by the co-operation 
of two elements, neither of which alone would be able to decompose the 
compound : neither carbon nor chlorine would, alone, decompose alumina, 
however high the temperature, but when the attraction of the carbon for 
the oxygen is added to that of the chlorine for the aluminium, the decom- 
position is easily effected. Aluminium chloride is also obtained by 
heating clay in a mixture of hydrochloric acid gas and vapour of carbon 
disulphide. The silica of the clay is converted into silicon tetrachloride 

(Sicy. 

* The great absorption and disappearance of heat during the evaporation of the water 
and ammonia from this alum, has led to its employment for filling the space between the 
double walls of fire-proof safes, which may become red hot outside, whilst the inside is 
kept below the scorching-pomt of paper. 

+ Small crystals of alumina resembling natural sapphire have been obtained by the 
action of vapour of aluminium fluoride upon boracic anhydride at a high temperature. 
By adding a little chromium fluoride, crystals similar to rubies and emeralds have been 
produced. 



294 ALUMINIUM. 

An impure solution of aluminium chloride is sold as a disinfectant 
under the name of chloralum. 

204. Aluminium. — In order to obtain this interesting metal, it is only 
necessary to pass the aluminium chloride in the state cf vapour over 
heated sodium, which removes the chlorine in the form of sodium chloride, 
leaving the aluminium as a white malleable metal about as hard as zinc, 
and fusing at a somewhat lower temperature than silver. For the 
extraction of aluminium upon the large scale, the alumina is not prepared 
from alum, but from the mineral known as Bauxite, which contains 
alumina, together with peroxide of iron and silica.* This mineral is 
heated with soda-ash (see page 263), when carbonic acid gas escapes, and 
the silica and alumina com Dine with soda to form silicate of soda, and a 
soluble compound of alumina with soda, which is generally called alumi- 
nate of soda, and has the composition 31\ T a. 2 O.Al 2 3 . On treating the 
mass with water, an insoluble silicate of alumina and soda is left, whilst 
the aluminate of soda is dissolved, and is obtained as an infusible mass 
when the solution is evaporated. This aluminate of soda is largely used 
by calico-printers as a mordant. To obtain alumina from it, the solution 
is neutralised with hydrochloric acid, which converts the sodium into 
chloride, and precipitates the alumina as hydrate of alumina (A1 2 3 .3H 2 0). 
As the next step towards the preparation of aluminium, the hydrate of 
alumina is mixed with charcoal and common salt, made up into balls, 
dried, and strongly heated in earthen cylinders through which dry chlorine 
is passed. The carbon abstracts the oxygen from the alumina, forming 
carbonic oxide, whilst the aluminium combines with the chlorine, and the 
aluminium chloride so formed combines with the chloride of sodium, 
and distils over as the double chloride of aluminium and sodium 
(Al 2 Cl 6 .2NaCl). This salt is then mixed with a proper proportion of 
metallic sodium, and heated in a reverberatory furnace, when the sodium 
combines with the chlorine of the aluminium chloride, leaving the metal 
to separate in a fused state beneath the melted sodium chloride, which 
protects it from oxidation. The aluminium may be rolled into sheets or 
drawn into wire. Commercial aluminium has been found to contain 
from 3 to 7 "5 per cent, of iron. Silicon is also present in it, as much as 
1 4 per cent, having been found in one sample. 

Aluminium is much more sonorous than most other metals. A bar of 
it suspended from a string, and struck with a hammer, emits a clear 
musical sound. It is remarkable as being the lightest metal capable of 
resisting the action of air even in the presence of moisture. Its specific 
gravity is 2*5. This lightness renders it valuable for the manufacture of 
small weights, such as the grain and its fractions, since these, when made 
of aluminium, are more than three times as large as when made of brass, 
and nearly nine times as large as platinum weights of the same denomina- 
tion. It is also employed for ornamental purposes, for though not so 
brilliant as silver, it is not blackened by sulphuretted hydrogen, which so 
easily affects that metal (page 196). 

Another characteristic feature of aluminium is its comparative resistance 
to the action of nitric acid even at a boiling heat. Z^o other metal com- 

* This mineral is found at Baux, near Aries, in the south of France, and in Antrim, 
Ireland ; it contains silica 13 to 17 per cent., alumina 60 to 65, peroxide of iron 4 to 8, 
water 15 to 17. When mixed with about 3 per cent, of clay and 6 per cent, of graphite it 
is said to form an excellent lining for steel-melting furnaces. 



MINERAL SILICATES OF ALUMINA. 295 

monly met with, except platinum and gold, is capable of resisting the 
action of nitric acid to the same extent. Hydrochloric acid, however, 
which will not attack gold and platinum, dissolves aluminium with 
facility, converting it into aluminium chloride, with disengagement of 
hydrogen ; Al 2 + 6HC1 = A1 2 C1 6 + H 6 . Solutions of potash and soda also 
easily dissolve it, forming the so-called aluminates of those alkalies ; 
thus 3NaHO + Al = Na 3 A10 3 + H 3 . Even when very strongly heated 
in air, aluminium is oxidised to a very slight extent, probably because 
the coating of alumina which is formed remains infusible and protects 
the metal beneath it. For a similar reason, apparently aluminium de- 
composes steam slowly, even at a high temperature. 

■ Aluminium decomposes water in the cold, if some aluminium iodide 
be present; hydrogen being set free and the aluminium hydrate pro- 
duced. 

When aluminium is fused with nine times its weight of copper, it forms 
an alloy very similar to gold in appearance, but almost as strong as iron. 
This alloy was strongly recommended to replace gold for ornamental pur- 
poses, but it does not retain its brilliancy so completely as that metal. 
Aluminium does not unite with mercury or with melted lead, both of 
which are capable of dissolving nearly all other metals. 

205. Mineral silicates of alumina. — Many of the chemical formulas of 
minerals which contain silicates of alumina associated with the silicates 
of other metallic oxides, are complicated, from the circumstance that a 
part of the aluminium is often replaced by iron, which, in the form of 
sesquioxide (Fe 2 3 ), is isomorphous with it, and therefore capable of re- 
placing it without altering the crystalline m form and general character 
of the mineral. In a similar manner, the other metals present in the 
mineral may be exchanged for isomorphous representatives ; thus there 
are two well-known felspars, potash-felspar (orthoclase) and soda-felspar 
(albite), having the formulas K 2 O.Al 2 3 .6Si0 2 and Na 2 O.Al 2 3 .6Si0 2 . 
These minerals are sometimes mingled in one and the same crystal 
(potash-albite or pericline) without bearing any definite equivalent pro- 
portion to each other ; the formula of such a mineral would be written 
(KNa) 2 O.Al 2 3 6Si0 2 . 

Porphyry has the same chemical composition as felspar. 

Mica, again, is composed essentially of magnesia, alumina, and silica 
(4MgO.Al 2 3 .4Si0 2 ), but part of the magnesium is so constantly re- 
placed by potassium and iron (as FeO), and part of the aluminium by 
iron (as Fe 2 3 ), that the general formula for mica must be written 
4(K 2 MgFe)0.(AlFe) 2 3 .4Si0 2 . 

Garnet is essentially a double silicate of alumina and lime, but often 
contains magnesium, iron, or manganese, replacing part of the calcium, 
and iron replacing part of the aluminium, being written — 

3(CaMgEeMn)0.(AlFe) 2 3 .3Si0 2 . 

This mineral is sometimes formed artificially in the slag of the iron blast- 
furnaces. 

Chlorite, a very important variety of rock, is a double silicate of 
alumina and magnesia, with variations as expressed by the formula — 

4(MgFe)0.(AlFe) 2 3 .2Si0 2 .3H 2 . 



296 PHOSPHATE OF ALUMINA. 

Basalt is a felspathic rock containing crystals of augite — 
4(CaMgFe)0.5Si0 2 . 

Cyanite, Kyanite, or Disthene, is a silicate of alumina (Al 2 3 .Si0 2 ), a 
crystal of which points north and south when freely suspended. 

Gneiss is chemically composed like granite, but the mica is arranged in 
regular layers. Trap rock contains felspar together with hornblende, 
which consists of silicates of alumina, lime, magnesia, and oxide of iron. 
Hornblende is sometimes found replacing the mica in granite, forming 
the rock called syenite. 

Lava, from volcanoes, consists essentially of ferrous, calcium and 
aluminium silicates ; the presence of a considerable proportion of potassium 
and of phosphoric acid renders the soil formed by the weathering of lava 
very fertile. 

Lapis lazuli, the valuable mineral which furnishes the natural ultra- 
marine used in painting, consists chiefly of silica and alumina, which con- 
stitute respectively 45 and 32 per cent, of it, but there are also present 
9 per cent, of soda, 6 per cent, of sulphuric acid, about 1 per cent, of sul- 
phur, and a somewhat smaller quantity of iron, together with a variable 
proportion of lime. The cause of its blue colour is not understood, since 
neither of its predominant constituents is concerned in the production of 
such a colour in other cases. In consequence of the rarity of the mineral, 
the natural ultramarine bears a very high price, but the artificial ultra- 
marine is manufactured in very large quantities at a low cost, and forms 
a very good imitation. One of the processes for preparing it consists in 
heating to bright redness in a covered crucible, for three or four hours, 
an intimate mixture of 100 parts of pure white clay (kaolin), 100 of dried 
carbonate of soda, 60 of sulphur, and 12 of charcoal. This would be 
expected to yield a mixture of silicate of soda, aluniinate of soda, and 
sulphide of sodium, the two first being white, and the latter yellow or 
brown, but the mass is found to have a green colour {green ultramarine). 
It is finely powdered, washed with water, dried, mixed with a fifth of its 
weight of sulphur, and gently roasted in a thin layer till the sulphur has 
burnt off, this operation being repeated, with fresh additions of sulphur, 
until the residue has a fine blue colour. In the opinion of some chemists, 
the presence of a small proportion of iron is essential to the blue colour, 
while others believe the colour to be due to sodium sulphide or tbio- 
sulphate, or both.'* Ultramarine is a very permanent colour under ordinary 
conditions of exposure to the air and light, but acids bleach it at once, 
with separation of gelatinous silica and evolution of sulphuretted hydrogen. 
Blue writing paper is often coloured with ultramarine, so that its colour 
is discharged by acids falling upon it in the laboratory. Chlorine also 
bleaches ultramarine. Starch is often coloured blue with this substance. 

Phosphate of alumina or aluminium phosphate is found naturally in 
several forms. It occurs in large quantities in the West India Islands. 
Turquoise is a hydrated aluminium phosphate (A1P0 4 ), owing its colour 
to the presence of oxide of copper, f Wavellite has the composition 
3A1 2 3 .2P 2 5 . None of the earlier analysts detected the phosphoric acid 
in this mineral, on account of the difficulty in separating it from the 

* Heumann assigns to ultramarine the formula 2Na 2 Al 2 Si 2 8 .Na 2 S 2 . 
f False or bone turquoise is fossil ivory, owing its colour to the presence of the natural 
blue phosphate of iron. 



GALLIUM. 297 

alumina, so that even in comparatively modern chemical works it is 
described as a hydrate of alumina. 

206. Thorinum is present in a rare Norwegian mineral thorite, where it is asso- 
ciated with silica, lime, magnesia, and other metallic oxides. The metal itself is 
similar to aluminium, but its oxide tlwrina appears to be a protoxide (ThO), and 
differs from alumina and glucina in being insoluble in the alkalies (potash, for 
example), though it dissolves in potassium carbonate. Moreover, the sulphate of 
thorina is sparingly soluble in hot water, so that it is precipitated on boiling its 
solution. Thorina is remarkable for its high specific gravity (9'4). 

207. Yttrium and Erbium are very rare metals found in gadolinite, a mineral 
silicate occurring at Ytterby in Sweden, and containing beside these, glucinum, 
cerium, and iron. Their oxides yttria (YO) and erbia resemble thorina in being 
insoluble in the alkalies, but soluble in their carbonates ; yttria is white, but erbia 
has a yellow colour. The salts of yttria and erbia are colourless. 

Terbia is an earth very similar to yttria, with which it is associated in the mineral 
Samarskite. 

Ytterbium is another metal recently found in gadolinite. 

208. Lanthanium (from XavOdvoo, to escape notice) is also found in cerite, but it 
differs from cerium in forming only one oxide (La. 2 3 ), which is white in the hydrated, 
but buff in the anhydrous state. When a mixture of nitrates of cerium and lantha- 
nium is calcined, sesquioxide of cerium and oxide of lanthanium are left, and may be 
separated by treatment with nitric acid, diluted with 100 parts of water, which 
dissolves only the latter. 

209. Didymium {Sldvfios, twin) is very similar to lanthanium, which is associated 
with it in cerite. It also forms but one oxide* (Di 2 3 ), which is violet when hydrated, 
and brown when anhydrous. It is insoluble in potash. The salts of didymium are 
either pink or violet. Their solutions have a remarkable power of absorbing some of 
the rays of the spectrum, so that the spectroscope affords a very delicate test for this 
metal, t 

210. Zirconium exists in the rare minerals zircon and hyacinth, in which its oxide 
zirconia (Zr0 2 ) is combined with silicic acid. Zirconia is somewhat similar to 
alumina, but it is insoluble in potash, and dissolves in potassium carbonate. Its sul- 
phate, moreover, is decomposed by boiling with potassium sulphate, which removes 
part of the sulphuric acid, and precipitates basic zirconium sulphate. Metallic 
zirconium somewhat resembles amorphous silicon, but it decomposes water slowly at 
the boiling-point, and has not been fused. 

Zirconia, made into a paste with solution of boracic acid, and strongly heated in 
iron moulds, yields masses which become even more brilliantly luminous than lime 
when heated in the flame of the oxyhydrogen blowpipe (zirconia light). 

211. Gallium is found in very small quantities in certain ores of zinc, particularly 
in the blende from Bensberg in the Pyrenees. The roasted ore is treated with enough 
sulphuric acid to dissolve nearly all the zinc. The residue containing the gallium is 
dissolved in sulphuric acid, and the solution partly precipitated with sodium car- 
bonate. The precipitate containing all the gallium and part of the zinc, is dissolved 
in sulphuric acid, largely diluted and boiled, to precipitate the titanic acid. The 
solution is mixed with acid ammonium acetate, and treated with hydrosulphuric acid. 
The precipitate, containing zinc and gallium, is dissolved in sulphuric acid, and again 
partially precipitated with sodium carbonate, which gives a deposit rich in gallium ; 
this is dissolved in exactly the required quantity of sulphuric acid, diluted and boiled, 
when basic gallium sulphate is deposited ; on dissolving this in potash and decom- 
posing the solution by the galvanic current, the gallium is deposited on the negative 
pole. 

Gallium is a hard white metal of sp. gr. 5*9, remarkable for its low fusing-point 
(30° C, 86° F.), so that it melts with the heat of the hand. It will remain liquid 
when cooled far below this temperature, but solidifies when touched with a piece of 
the solid metal. 

* According to Frerichs, two, viz., DiO and Di 2 3 , to which Brauner has added Di 2 C>5. 

f The mineral rliabdophane found in Cornwall, and formerly believed to contain zinc 
sulphide, has been shown by Hartley to be a hydrated phosphate of cerium, didymium, 
lanthanium, and yttrium, with the general formula K"'P0 4 .H 2 0. 



298 URANIUM. 

It is not oxidised by dry air until heated nearly to redness, and the oxidation is 
then only superficial. Nitric acid scarcely acts upon it in the cold, but dissolves it 
on heating. Hydrochloric acid dissolves it, with evolution of hydrogen. Potash has 
a similar action. 

Gallium forms two chlorides, GaCl 2 and Ga 2 Cl 6 ; they are very fusible, volatile, and 
deliquescent. 

Gallium sulphate is very soluble in water ; the solution deposits a basic salt when 
boiled. It combines with ammonium sulphate to form an alum, the solution of 
which is also precipitated by boiling. 

Ammonia precipitates solutions of gallium, but the precipitate is more easily soluble 
in excess than in the case of aluminium. Ammonium sulphide gives a precipitate 
only if zinc be present, when the gallium is precipitated together with the zinc. 
Potash gives a precipitate which dissolves easily in excess. Potassium ferrocyanide 
produces a white precipitate. 

The most delicate test for gallium is the production of two violet bands in the 
spectrum, when an induction spark passes from the positive terminal of a secondary 
coil to the surface of the solution under examination into which the negative terminal 
of the coil is made to dip. 

From the description of its properties, it will be seen that gallium bears consider- 
able resemblance to aluminium, and it is probable that its oxide has the formula 
Ga 2 3 . 

212. Indium is the name of a metal which has recently been discovered, with the 
help of the spectroscope, in a specimen of blende from Freiberg. Its name refers to 
an indigo blue line in the spectrum. The examination of the metal is as yet imper- 
fect, but it is white, malleable, and dissolves, like zinc and cadmium, in hydrochloric 
acid. Its specific gravity is 7 '42. Fusing-point 176° C. Less easily converted into 
vapour than zinc or cadmium. Indium dissolves in HC1, forming InCl 3 , in HN0 3 , 
forming In(N0 3 ) 3 , and in H 2 S0 4 , forming In 2 (S0 4 ) 3 which crystallises with 9H 2 0. 

Ammonia produces, in solutions of indium, a white precipitate, ln(OH) 3 ; insoluble 
in excess. Ammonium carbonate gives a precipitate soluble in excess and reprecipi- 
tated by boiling. To extract indium from the Freiberg zinc, the metal is boiled 
with dilute sulphuric acid, employed in such quantity as to leave part of the zinc 
undissolved, together with indium and lead. The residue is dissolved in nitric acid, 
the lead and cadmium precipitated by hydrosulphuric acid, the latter expelled by 
boiling, and the oxide of indium precipitated from the solution by barium carbon- 
ate. When this precipitate is dissolved in hydrochloric acid, and excess of ammonia 
added, the white indium hydrate is precipitated, and may be reduced by heating in 
hydrogen. 

At a bright red heat it burns with a violent blue flame, yielding a yellow oxide of 
indium, ln 2 3 . 

The atomic weight of indium is 113*4. 

213. Cerium is found in gadolinite, but more abundantly in cerite, which is 
essentially a silicate of cerium. Phosphate of cerium (cryptoHte) has also been found 
in brown apatite. The mineral jluoceritc is Ce 2 F 6 , and fluocerine is an oxyfluoride. 
This metal has been employed medicinally, in the form of oxalate of cerium. 
It forms two basic oxides, cerous oxide, Ce 2 3 , which forms colourless salts, and 
eerie oxide, Ce0 2 , which is yellow, and gives yellow or red salts. In this respect 
cerium more nearly resembles iron than aluminium. These oxides of cerium are 
insoluble in the alkalies ; cerous oxide is easily precipitated from its salts by oxalic 
acid in the form of the oxalate mentioned above. Ceric oxide does not appear to 
form a corresponding chloride, but yields cerous chloride and free chlorine when 
heated with hydrochloric acid. Tetrafluoride of cerium, CeF 4 , has been obtained. 

214. Uranium. — This is a rare metal, never employed in the metallic state, but in 
the form of sesquioxide (U 2 3 ) and black oxide (2UO. U 2 3 ), for imparting yellow and 
black colours respectively to glass and porcelain. The chief source of these compounds 
is the mineral pitch-blende, which contains a large proportion of black oxide of 
uranium, together with silica, iron, copper, lead, and arsenic. In its chemical 
relations uranium presents some similarity to iron and manganese. It forms two 
distinct oxides, UO and U 2 3 , of which the former is decidedly basic, whilst the 
latter is capable of acting "both as an acid and a base. The bright greenish-yellow 
colour of tne salts of the sesquioxide of uranium is characteristic of the metal, and 
glass coloured with this oxide exhibits the remarkable optical effect of fluorescence in 
a very high degree. 



IRON. 



299 



The uranic salts (derived from U 2 3 ) are reduced to uranous salts (derived from 
LTO) by the action of light in the presence of organic substances. 

The vapour-densities of the tetrachloride and tetrabromide of uranium lead to 240 
(instead of 120) as the atomic weight of this metal. 



IROK 

Fe" = 56 parts by weight. 

215. This most useful of all metals is one of those most widely aud 
abundantly diffused in nature. It is to be found in nearly all forms of 
rock, clay, sand, and earth, its presence in these being commonly indi- 
cated by their colours, for iron is the commonest of natural mineral 
colouring ingredients. It is also found, though in small proportion, in 
plants, and in larger quantity in the bodies of animals, especially in the 
blood, which contains about 0'5 per cent, of iron in very intimate associ- 
ation with its colouring matter. 

But iron is very rarely found in the metallic state in nature, being 
almost invariably combined either with oxygen or sulphur. 

Metallic iron is met with, however, in the meteorites or metallic masses, 
sometimes of enormous size, and of unknown origin, which occasionally 
fall upon the earth. Of these iron is the chief component, but there are 
also generally present cobalt, nickel, chromium, manganese, copper, tin, 
magnesium, carbon, phosphorus, and sulphur. 

The chief forms of combination in which iron is found in sufficient 
abundance to render them available as sources of the metal, are shown in 
the following table : — 

Ores of Iron. 



Common Name. 


Chemical Name. 


Composition. 


Magnetic iron ore 


Ferroso-ferric oxide 


Fe 3 4 


Red hsematite 


Ferric oxide 


Fe 2 3 


Specular iron 




5J 


Brown haematite 


Ferric hydrate 


2Fe. 2 3 .3H 2 


Spathic iron ore 


Ferrous carbonate 


FeC0 3 


Clay iron-stone 


Ferrous carbonate with clay 




Blackband 


\ Ferrous carbonate with clay and 
| bituminous matter 






Iron pyrites 


Bisulphide of iron 


FeS 2 



These ores are frequently associated with extraneous minerals, some of 
the constituents of which are productive of injury to the quality of the 
iron. lb is worthy of notice that scarcely one of the ores of iron is 
entirely free from sulphur and phosphorus, substances which will be seen 
to have a very serious influence on the quality of the iron extracted from 
them, and the presence of which increases the difficulty of obtaining the 
metal in a marketable condition. 

The following table illustrates the general composition of the most 
important English ores of iron, with reference to the proportions of iron, 
and of those substances which materially influence the character of the 
iron extracted from the ore, viz., manganese (present as oxide or car- 
bonate), phosphorus (present as phosphates), and sulphur (present as 
bisulphide of iron). The maximum and minimum quantities found in 
each ore are specified. 



300 



ORES OF IRON. 



British Iron Ores.* 



In 100 parts. 


Iron. 


Oxide of 

Manganese, 

MnO. 


Phosphoric 

Anhydride, 

P 2 5 . 


Bisulphide 

of Iron 
(Pyrites). 


No. of 
Samples . 
Analysed. 


Clay iron-stone from coal-measures, 
Clay iron-stone from the lias, 
Brown haematite, .... 
Red haematite. .... 
Spathic ore 

Magnetic ore, .... 


Max. Min. 

43-30 20-95 
49-17 17-34 
63-04 11-98 
69-10 47-47 
49-78 13-98 

5701 


Max. ! Min. 

3-30 0-46 
1-30 
1-60 trace 
1-13 trace 
12-64 1-93 

0-14 


Max. Min. 

1-42 0-07 
5-05 
3-17 
trace trace 
0-22 

0-10 


Max. Min. 

1-21 
1-60 
0-30 
0-06 
0-11 

0-07 


77 

12 

23 

5 

6 

1 



From this table it will be gathered that, among the most abundant of 
the iron ores of this country, red haematite is the richest and purest, 
whilst the brown haematite often contains considerable proportions of 
sulphur and phosphorus, and the spathic ore, though containing little 
sulphur and phosphorus, often contains much manganese. 

The argillaceous ores, or clay iron-stones found in the lias, contain more 
phosphorus than those from the coal-measures ; and these latter, as a 
general rule, contain more sulphur (pyrites) than the former, although the 
maximum in the table does not show this. 

Clay iron-stone is the ore from which the largest quantity of iron is 
extracted in England, since it is found abundantly in the coal-measures 
of Staffordshire, Shropshire, and South Wales; and it is a circumstance of 
great importance in the economy of English iron-smelting, that the coal 
and limestone required in the smelting process, and even the fireclay em- 
ployed in the construction of the furnace, are found in the immediate 
vicinity of the ore. 

Blackband is the clay iron-stone found in the coal-fields of Scotland, 
and often contains between 20 and 30 per cent, of bituminous matter, 
which contributes to the economy of fuel in smelting it. 

Red licematite (Fe 2 3 ) is the most characteristic of the ores of iron, 
occurring in hard shining rounded masses, with a peculiar fibrous structure 
and a dark red-brown colour, whence the ore derives its name (alfxa, blood). 
It is found in considerable quantities in Lancashire and Cornwall, but 
unfortunately its very compact structure is an obstacle to its being smelted 
alone, so that it is generally mixed with some clay iron-stone, and hence 
the iron obtained is not so free from sulphur and phosphorus as if it were 
extracted from haematite alone. 

Red ochre is a soft variety of this ore, containing a little clay. 

Brown hcematite (2Fe 2 3 .3H 2 0) is found at Alston Moor (Cumberland) 
and in Durham, but it is more abundant on the Continent, and is the 
source of most of the Belgian and French irons. Pea iron ore and yellow 
ochre are varieties of brown haematite. The Scotch ore, called kidney-form 
clay iron-stone, is really a hydrated sesquioxide of iron. 

Specular iron ore (Fe 2 3 ) (oligist ore or iron-glance), although of the 
same composition as red haematite, is very different from it in appearance, 
having a steel-grey colour and a brilliant metallic lustre. The island of 
Elba is the chief locality where this ore is found, but it also occurs in 
Germany, France, and Eussia. The excellent quality of the iron smelted 
from this ore is due partly to the purity of the ore, and partly to the cir- 
cumstance that charcoal, and not coal, is employed in smelting it. 

* This table has been compiled from, the analyses given in Percy On Iron and Steel. 



METALLURGY OF IRON. 301 

Magnetic iron ore (Fe 3 4 ), of which, the loadstone is a variety, has a 
more granular structure, and a dark iron-grey colour. It forms moun- 
tainous masses in Sweden, and is also found in Russia and North 
America. It is generally smelted with charcoal, and yields an excellent 
iron. Iron sand, a peculiar heavy black sand of metallic lustre, con- 
sists in great measure of the magnetic ore, but contains a very large pro- 
portion of titanium. It is found abundantly in India, Nova Scotia, and 
New Zealand; but its fine state of division prevents it from being largely 
available as a source of iron. 

Spathic iron ore (FeC0 3 ) is found in abundance in Saxony, and often 
contains a considerable quantity of manganese carbonate, which influences 
the character of the metal extracted from it. 

The oolitic iron ore, occurring in the Northampton oolite, contains both 
hydrated sesquioxide and carbonate of iron, together with clay. 

Iron pyrites (FeS 2 ) is remarkable for its yellow colour, its brilliant 
metallic lustre and crystalline structure, being generally found either in 
distinct cubical or dodecahedral crystals, or in rounded nodules of radiated 
structure. It was formerly disregarded as a source of iron, on account of 
the difficulty of separating the sulphur ; but since the demand for iron 
has so largely increased, an inferior quality of the metal has been extracted 
from the residue left after burning the pyrites in the manufacture of oil of 
vitriol (page 206), the residue being first well roasted in a lime-kiln to 
remove as much as possible of the sulphur. 

The quantity of iron ore raised annually in this country is estimated at 
about 16 million tons, of which about 9 millions are clay and calcareous 
iron-stones (chiefly the former) from the lias formations of North York 
shire, Lincolnshire, Northamptonshire, Oxford, and Wiltshire ; 4J mil- 
lions are clay iron-stones of the coal formations in Scotland, England, and 
Wales ; and about 2 \ millions are haematites and spathic ores. 

216. Metallurgy of iron. — Iron owes the high position which it occupies 
among useful metals to a combination of valuable qualities not met with 
in any other metaL Although possessing nearly twice as great tenacity or 
strength as the strongest of the other metals commonly used in the metallic 
state, it is yet one of the lightest, its specific gravity being only 7*7, and 
is therefore particularly well adapted for the construction of bridges and 
large edifices, as well as for ships and carriages. It is the least yielding 
or malleable of the metals in common use, and can therefore be relied 
upon for affording a rigid support ; and yet its ductility is such that it 
admits of being rolled into the thinnest sheets and drawn into the finest 
wire, the strength of which is so great that a wire of -j^th inch in dia- 
meter is able to sustain 705 pounds, while a similar wire of copper, which 
stands next in order of tenacity, will not support more than 385 pounds. 

Being, with the exception of platinum, the least fusible of useful metals, 
iron is applicable to the construction of fire-grates and furnaces. Nor are 
its qualifications all dependent upon its physical properties, for it not only 
enters into a great number of compounds which are of the utmost use in 
the arts, but its chemical relations to one of the non-metallic elements, 
carbon, are such, that the addition of a small quantity of this element 
converts it into steel, far surpassing iron in the valuable properties of hard- 
ness and elasticity ; whilst a larger quantity of carbon gives rise to cast- 
iron, the greater fusibility of which permits it to be moulded into vessels 
and shapes which could not be produced by forging. 



302 



EXTRACTION OF IRON FROM CLAY IRON-STONE. 



217. English process of smelting clay iron-stone. — The first step 
towards the extraction of the metal consists in calcining (or roasting) the 
ore, in order to expel water and carbonic acid gas. To effect this the ore 
is built up, together with a certain amount of small coal, into long pyra- 
midal heaps, resting upon a foundation of large lumps of coal ; blackband 
often contains so much bituminous matter that any other fuel is unneces- 
sary. These heaps are kindled in several places, and allowed to burn 
slowly until all the fuel is consumed. This calcination has the effect of 




Fig. 243. — Blast-furnace for smelting iron ores. 

rendering the ore more porous, and better fitted for the smelting process. 
If the ore contained much sulphur, a part of it would be expelled by the 
roasting in the form of sulphurous acid gas. 

Sometimes the calcination is effected in kilns resembling lime-kilns, and 
it is often altogether omitted as a separate process, the expulsion of the 
water and carbonic acid gas being then effected in the smelting-furnace 
itself as the ore descends. 

The calcined ore is smelted in a huge blast-furnace (fig. 243) about 
fifty or sixty feet high, built of massive masonry, and lined internally with 
firebrick. Since it would be impossible to obtain a sufficiently high 
temperature with the natural draught of this furnace, air is forced into it 
at the bottom, under a pressure of three or four pounds upon the inch, 
through three tuyere pipes, the nozzles of which pass through apertures in 
three sides of the furnace. 



CHEMICAL CHANGES IN THE BLAST-FUENACE. 303 

It would be very easy to reduce to the metallic state the oxide of iron 
contained in the calcined ore, by simply throwing it into this furnace, 
together with a proper quantity of coal, coke, or charcoal ; but the metallic 
iron fuses with so great difficulty, that it is impossible to separate it from 
the clay unless this latter is brought into a liquid state ; and even then, 
the fusion of the iron, which is necessary for complete separation, is only 
effected after it has formed a more easily fusible compound with a small 
proportion of carbon derived from the fuel. 

Now, clay is even more difficult to fuse than iron, so that it is neces- 
sary to add, in the smelting of the ore, some substance capable of forming 
with the clay a combination which is fusible at the temperature of the 
furnace. If clay (silicate of alumina) be mixed with limestone (carbonate 
of lime), and exposed to a high temperature, carbonic acid gas is expelled 
from the limestone, and the lime unites with the clay forming a double 
silicate of alumina and lime, which becomes perfectly liquid, and when 
cool, solidifies to a glass or slag. The limestone is here said to act as a 
flux, because it induces the clay to flow in the liquid state. In order, 
therefore, that the clay may be readily separated from the metallic iron, 
the calcined ore is mixed with a certain proportion of limestone before 
being introduced into the furnace. 

Great care is necessary in first lighting the blast-furnace lest the new 
masonry should be cracked by too sudden a rise of temperature, and when 
once lighted, the furnace is kept in constant work for years until in want of 
repair. When the fire has been lighted, the furnace is filled up with coke, 
and as soon as this has burnt down to some distance below the chimney, a 
layer of the mixture of calcined ore with the requisite proportion of lime- 
stone is thrown upon it ; over this there is placed another layer of coke, 
then a second layer of the mixture of ore and flux, and so on, in alternate 
layers, until the furnace bas been filled up ; when the layers sink down, 
fresh quantities of fuel, ore, and flux are added, so that the furnace is kept 
constantly full. As the air passes from the tuyere pipes into the bottom 
of the furnace, it parts with its oxygen to the carbon of the fuel, which it 
converts into carbonic acid gas (C0 2 ) ; the latter, passing over the red hot 
fuel as it ascends in the furnace, is converted into carbonic oxide (CO) by 
combining with an additional quantity of carbon. It is this carbonic 
oxide which reduces the calcined ore to the metallic state, when it comes 
in contact with it, at a red heat, in the upper part of the furnace, for 
carbonic oxide removes the oxygen, at a high temperature, from the oxides 
of iron, and becomes carbonic acid gas ; the iron being left in the metallic 
state. But the iron so reduced remains disseminated through the mass 
of ore until it has passed down to a part of the furnace which is more 
strongly heated, where the iron enters into combination with a small pro- 
portion of carbon to form cast-iron, which fuses and runs down into the 
crucible or cavity for its reception at the bottom of the furnace. At the 
same time, the clay contained in the ore is acted upon by the lime of the 
flux, producing a double silicate of alumina and lime, which also falls 
in the liquid state into the crucible, where it forms a layer of " slag " 
above the heavier metal. This slag, which has five or six times the bulk 
of the iron, is allowed to accumulate in the crucible, and to run over 
its edge down the incline upon which the blast-furnace is built ; but 
when a sufficient quantity of cast-iron has collected at the bottom of 
the crucible, it is run out through a hole provided for the purpose, either 



304 THE HOT BLAST. 

into channels made in a bed of sand, or into iron moulds, where it is cast 
into rough semi-cylindrical masses called pigs, whence cast-iron is also 
spoken of as pig-iron. The temperature of the furnace is, of course, 
highest in the immediate neighbourhood of the tuyeres : the reduction of 
the iron to the metallic state appears to commence at about two-thirds of 
the way down the furnace, the volatile matters of the ore, fuel, and flux 
being driven off before this point is reached, 

Some idea may be formed of the immense scale upon which the smelt- 
ing of iron ores is carried out, when it is stated that each furnace con- 
sumes, in the course of twenty-four hours, about 50 tons of coal, 30 tons 
of ore, 6 tons of limestone, and 100 tons of air. The cast-iron is run off 
from the crucible once or twice in twelve hours, in quantities of five 
or six tons at a time. The average yield of calcined clay iron-stone is 
35 per cent, of iron. 

The gases escaping from the chimney of the blast-furnace are highly 
inflammable, for they contain, beside the nitrogen of the air blown into 
the furnace, a considerable quantity of carbonic oxide and some hydrogen, 
together with the carbonic acid gas formed by the action of the carbonic 
oxide upon the ore. Since the carbonic oxide and hydrogen confer con- 
siderable heating power upon these gases, they are employed, in some 
iron- works, for heating steam-boilers, or for calcining the ore, or for raising 
the temperature of the blast. 

The composition of the gas issuing from a hot-blast furnace (fed with uncoked 
coal) may be judged of from the following table : — 



Gas from 


Blast- Furnace. 


Nitrogen, . 


. 55-35 vols 


Carbonic oxide, . 


. 25-97 ,, 


Hydrogen, . 


. 673 „ 


Carbonic acid gas, 


. . . 7-77 „ 


Marsh gas, 


. 3-75 ,, 


Oleiiant gas, 


. 0-43 „ 



100-00 „ 

The carbonic oxide, of course, renders these gases highly poisonous, and fatal acci- 
dents occasionally happen from this cause. 

Although the bulk of the nitrogen present in the air escapes unchanged from the 
furnace, it is not improbable that a portion of it contributes to the formation of the 
cyanide of potassium (KCN), which is produced in the lower part of the furnace, the 
potassium being furnished by the ashes of the fuel. 

The hot blast. — On considering the enormous quantity of air which- 
passes through the blast-furnace, it will be seen that it occasions the loss 
of a considerable amount of heat. In order to economise the fuel, hot- 
blast furnaces are fed with air of which the temperature is raised to about 
600° F., by passing it through heated iron pipes or over hot firebricks 
before allowing it to enter the blast-furnace. The higher temperature 
which is thus attained permits the use of uncoked coal, which would not 
have given enough heat in a cold -blast furnace, and the same quantity of 
ore may be smelted with less than half the coal formerly employed, since 
the blast may be heated by means of the waste heat of the furnace. It 
appears, however, that the hot-blast iron is inferior in quality to that 
obtained from the same ore in a cold-blast furnace, and this is generally 
explained by referring to the larger quantity of sulphur contained in the 
raw coal ; to the circumstance, that the cast-iron being exposed to a much 



SLAG FROM CAST-IRON. 305 

higher temperature in the hot-blast furnace is more liable to receive and 
retain a larger amount of foreign substances ; and (most important of 
all) to the custom of extracting iron in a hot-blast furnace from slags 
obtained in the subsequent processes of the iron-manufacture, which could 
not be smelted in a cold-blast furnace. These slags always contain sulphur 
and phosphorus, and therefore yield an inferior quality of iron. Hence the 
distinction commonly drawn between mine iron extracted from the ore 
without admixture of slags, and cinder iron (or kentledge) in the preparation 
of which slag or cinder has been employed. 

The sl'jg from the blast furnace is essentially a glass composed of a 
double silicate of aluminium and calcium, the composition of which varies 
much according to the nature of the earthy matters in the ore, and the 
composition of the flux. Its colour is generally grey, streaked with blue, 
green, or brown. 

The nature of the flux employed must, of course, be modified according 
to the composition of the earthy substances (or gangue) present in the ore. 
Where this consists of clay (silicate of alumina) the addition of lime 
(which is sometimes added in the form of limestone and sometimes as 
quicklime) will provide for the formation of the double silicate of alumina 
and lime. But if the iron-ore happened already to contain limestone, an 
addition of clay would be necessary, or if quartz were present, consisting, 
of silica only, both lime and alumina (in the form of clay) will be neces- 
sary as a flux. It is sometimes found economical to employ a mixture of 
ores containing different kinds of gangue, so that one may serve as a flux 
to the other. If a proper proportion of lime were not added, a portion of 
the oxide of iron would combine with the silica and be carried off in the 
slag ; but if too large a quantity of lime be employed, it will diminish the 
fusibility of the slag, and prevent the complete separation of the iron from 
the earthy matter. The most easily fusible slag which can be formed by 
the action of lime upon clay has the composition 6CaO.Al 2 3 .9Si0 2 ; 
but in English furnaces, where coal and coke are employed, it is found 
necessary to employ a larger proportion of lime to convert the sulphur of 
the fuel into calcium sulphide, so that the slag commonly has a composi- 
tion more nearly represented by the formula, 12Ca0.2Al 2 3 .9Si0 9 , which 
would express a compound of 6 molecules of normal calcium silicate with 
1 molecule of normal aluminium silicate, 6Ca 2 Si0 4 .Al 4 (Si0 4 ) 3 . 

Since iron, manganese, and magnesium are commonly found occupying 
the place of a portion of the calcium, a more general formula for the slag 
from English blast-furnaces would be 6(CaEeMnMg) 2 Si0 4 .Al 4 (Si0 4 ) 3 . 

A fair impression of the ordinary composition of the slag from blast- 
furnaces is conveyed by the following table : — 

Slag from Blast-Furnace. 

Silica, 43-07 

Alumina, . . . . . . . . 14*85 

Lime, 28 '92 

Magnesia, . . , . . . . 5 "87 

Oxide of iron (FeO), . . . . . . 2*35 

Oxide of manganese (MnO), • . . . . 1*37 

Potash, ........ 1-84 

Sulphide of calcium 1 '90 

Phosphoric acid, ....... trace 

100-17 

U 



306 COMPOSITION OF CAST-IRON. 

These slags are sometimes run from the blast-furnace into iron moulds, 
in which they are cast into blocks for rough building purposes. The 
presence of a considerable proportion of potash has led to experiments 
upon their employment as a manure, for which purpose they have been 
blown out, when liquid, into a finely-divided frothy condition fit for 
grinding and applying to the soil. By blowing steam through the slag it 
is converted into a substance resembling spun glass, and used under the 
name of mineral cotton, for packing round steam-pipes, &c. 

218. Cast-Iron is, essentially, composed of iron with from 2 to 5 per 
cent, of carbon, but always contains other substances derived either from 
the ore or from the fuel employed in smelting it. On taking into con- 
sideration the energetic deoxidising action in the blast-furnace, it is not 
surprising that portions of the various oxygen compounds exposed to it 
should part with their oxygen, and that the elements thus liberated 
should find their way into the cast-iron. In this way the silica is reduced, 
and its silicon is found in cast-iron in quantity sometimes amounting 
to 3 or 4 per cent. Haematite pig is usually rich in silicon, from the 
presence of silica in an easily reducible condition in the ore. Sulphur 
and phosphorus are also generally present in cast-iron, but in very much 
smaller quantity ; their presence diminishes its tenacity, and the smelter 
endeavours to exclude them as far as possible, though a small quantity of 
phosphorus appears to be rather advantageous for some castings, since it 
augments the fusibility and fluidity of the cast-iron. The sulphur is 
chiefly derived from the coal or coke employed in smelting, and for this 
reason charcoal would be preferable to any other fuel if it could be 
obtained at a sufficiently cheap rate. The iron-works of America and 
those of the European continent enjoy a great advantage in this respect over 
those of England. The phosphorus is obtained chiefly from the phos- 
phoric acid existing in the ore or in the flux.* It appears to exist in the 
iron, at least in some cases, as Ee 4 P. The proportion of phosphorus taken 
up by the cast-iron increases with the temperature of the blast-furnace. 
Manganese, amounting to 1 or 2 per cent., is often met with in cast-iron, 
having been reduced from the oxide of manganese, which is generally 
found in iron ores. Other metals, such as chromium, cobalt, &c, are also 
occasionally present, though in so small quantities as to be of no importance 
in practice. 

The following table exhibits the largest and smallest proportion of the 
various elements determined in the analysis of upwards of a hundred 
specimens of cast-iron : — 

Composition of Cast-Iron, f • 

Carbon, 

Silicon, 

Sulphur, . 

Phosphorus, 

Manganese, 

Iron, 

In order to understand the difference observed in the several varieties 
of cast-iron, it is necessary to consider the peculiar relations between iron 
and carbon. Iron fused in contact with carbon is capable of combining 

* Phosphorus, in the form of phosphates, is sometimes found in coal, 
f Compiled from Percy On Iron and Steel. 



Maximum. 


Minimum. 


4-81 


1 '04 per cent 


. . . . 4-77 


08 


1-06 


o-oo 


. . . . 1-87 


trace , , 


6-08 


trace ,, 



GKEY, MOTTLED, AND WHITE IRON. 



307 



with nearly 6 per cent, of that element, to form a white, brilliant, and 
brittle compound, which may be represented pretty nearly as composed 
of Fe 4 C. Under certain circumstances, as this compound of iron and 
carbon cools, a portion of the carbon separates from the iron, and remains 
disseminated throughout the mass in the form of minute crystalline par- 
ticles very much resembling natural graphite. If a broken piece of iron 
containing these scales be examined, the fracture will be found to exhibit 
a more or less dark grey colour, due to the presence of the uncombined 
carbon, and for this reason a cast-iron in which a portion of the carbon 
has thus separated is commonly spoken of as grey iron, whilst that in 
which the whole of the carbon has remained in combination with the 
metal exhibits a white fracture, and is termed white iron or bright iron. 
Intermediate between these is the variety known as mottled iron, which 
has the appearance of a mixture of the grey and white varieties. 

The different condition of the carbon in the two varieties of cast-iron is 
rendered apparent when the metal is dissolved in diluted sulphuric or 
hydrochloric acid, for any carbon which exists in the uncombined state 
will then be left, whilst that which had been in combination with the 
iron passes off in the form of peculiar compounds of carbon and hydrogen, 
which impart the disagreeable odour perceived in the gas evolved when 
the metal is dissolved in an acid. 

The properties of these two varieties of cast-iron are widely different, 
grey iron being so soft that it may be turned in a lathe, whilst the white 
iron is extremely hard, and of higher specific gravity. Again, although 
white iron fuses at a lower temperature than grey iron, the latter is far 
more liquid when fused, and is therefore much better fitted for casting. 

Although the presence of uncombined carbon is the chief point which 
distinguishes grey from white iron, other differences are commonly observed 
in the composition of the two varieties. The white iron usually contains 
less silicon than grey iron, but a larger proportion of sulphur. White 
iron also usually contains a much larger quantity of manganese. 

The difference in the composition of these three varieties of cast-iron is 
shown in the following table : — 





Grey. 


Mottled. 


White. 


Iron, .... 


90-24 


89-31 


89-86 


Combined carbon, 


1-02 


179 


2-46 


Graphite, 


2-64 


1-11 


0-87 


Silicon, 


3-06 


2-17 


1-12 


Sulphur, 


114 


1-48 


2-52 


Phosphorus, 


0-93 


1-17 


0'91 


Manganese, . . 


0-83 


1-60 


2-72 


99-86 


98-63 


100-46 



As might be expected, it is not easy to tell where a cast-iron ceases to 
be grey and begins to be mottled, or where the mottled iron ends and 
wdiite iron begins. There are, in fact, eight varieties of cast-iron in com- 
merce, distinguished by the numbers one to eight, of which No. 1 is dark 
grey, and contains the largest proportion of graphite, which diminishes in 
the succeeding numbers up to No. 8, which is the whitest iron, the inter- 
mediate numbers being more or less mottled. 

The particular variety of cast-iron produced is to some extent under 



308 REFINING CAST-IRON. 

the control of the smelter ; a furnace in good order appearing usually to 
yield grey iron, whilst a defective furnace, or one supplied with too small 
a proportion of fuel, will commonly give a white iron. But the metal 
sometimes varies considerably at different levels in the crucible of the 
furnace, so that pigs of different degrees of greyness are obtained at the 
same tapping. 

Mottled cast-iron surpasses both the other varieties in tenacity, and is 
therefore preferred where this quality is particularly desirable. 

The dark grey iron used for casting, known as foundry-iron, is produced 
at a higher temperature, by supplying the blast-furnace with a larger pro- 
portion of fuel than is employed in making the lighter forge-iron destined 
for conversion into wrought-iron. The extra consumption of fuel, of 
course, renders the foundry-iron more expensive. When a furnace is 
worked with a low charge of fuel to produce a white iron, a larger quan- 
tity of iron is lost in the slag, sometimes amounting to 5 per cent, of 
the metal, whilst the average loss in producing grey iron does not exceed 
2 per cent. Ores containing a large proportion of manganese are generally 
found to yield a white iron. 

When grey iron is melted, the particles of graphite to which its grey 
colour is due are dissolved by the liquid iron, and if it be poured into 
a cold iron mould so as to solidify it as rapidly as possible, the external 
portion of the casting will present much of the hardness and appear- 
ance of white iron, the sudden cooling having prevented the separation 
of the graphite. This affords the explanation of the process of chill- 
casting, by which shot, &c, made of the soft fusible grey iron, are made 
to acquire, externally, a hardness approaching that of steel. It is a com- 
mon practice to produce compound castings, that portion of the mould 
where chilling and consequent hardness is required being made of thick 
cast-iron, and the other part, which is to give a tougher and a softer casting, 
of sand. 

When white pig-iron is melted at an extremely high temperature (in a 
Siemens' furnace) and slowly cooled, it becomes grey. 

The specific gravity of cast-iron > varies between 6*92 (grey) and 7 "53 
(white), and its fusing-point is somewhat below 3000° F. 

Recent experiments throw some doubt upon the existence of carbon in a state of 
actual chemical combination in cast-iron. It has been found that, when acting upon 
mercuric chloride, white cast-iron generates considerably more heat than pure iron ; 
this would indicate that absorption of heat had taken place in the formation of white 
cast-iron (which contained 4 per cent, of "combined" carbon), whereas, had the 
carbon combined chemically with the iron, generation of heat should have taken 
place. On the other hand, it was found by the same method, that manganese and 
carbon do generate heat, and therefore enter into true chemical combination. This 
fact may have some bearing upon the use of manganese in the manufacture of steel. 

Conversion of Cast-Iron into Bar or Wrought-Iron. 

219. In order to convert cast-iron into bar-iron, it -is necessary to reduce 
it as far as possible to the condition of pure iron, by removing the carbon, 
silicon, and other substances associated with it. This purification is 
effected upon the principle, that when cast-iron is strongly heated in con- 
tact with oxide of iron, its carbon is evolved in the form of carbonic oxide, 
whilst the silicon, also combining with the oxygen from a part of the 
oxide of iron, is converted into silica, which unites with another portion 
of the oxide to form a fusible slag easily separated from the metal. 



REFINING CAST-IRON. 



309 




Fig. 244. — Hearth for refining pig-iron. 



The most important of the processes employed for the conversion 
of pig-iron into bar-iron, is that known as the puddling process, but 
this is sometimes preceded by the process of refining, which will therefore 
be first described. 

Refining cast-iron. — This process consists essentially in exposing the 
metal, in the fused state, 
to the action of a blast 
of air. The refinery 
(figs. 244, 245) is a 
rectangular trough with 
double walls of cast-iron, 
between which cold 
water is kept circulating 
to prevent their fusion. 
This trough is about 3 J 
feet long by 2J wide, 
and usually lined with 
fireclay ; on each side 
of it are arranged three 
tuyere pipes for the sup- 
ply of air, inclined at an 
angle of 25° to 30° to 
the bottom of the fur- 
nace, which is fed with coke, unless the very best iron is required, as for 
the manufacture of tin-plate, when charcoal is generally used in the 
refinery. 

This furnace having been filled to a certain height with fuel, five or six 
pigs of iron (from 20 to 30 cwt.) are arranged symmetrically upon it, and 
covered with coke, a blast of air being forced in through the tuyeres, 
under a pressure of about 3 lbs. upon the inch. In about a quarter of 
an hour the metal begins 
to fuse gradually, and to 
trickle down throughthe 
fuel to the bottom of 
the refinery, a portion of 
the iron being converted 
into oxide in its descent, 
by the air issuing from 
the tuyere pipes. When 
the whole of the metal 
has been fused, the air 
is still allowed to play 
for some time upon its 
surface, when the fused 
metal appears to boil 
in consequence of the 
escape of bubbles of 
carbonic oxide. 

After about two hours the tap-hole is opened, and the molten metal 
run out into a flat cast-iron mould kept cold by water, in order to chill 
the metal and render it brittle. The plate of refined iron thus obtained 
is usually about 2 inches thick. The slag (or finery cinder) is generally 




Fig. 245. — Hearth for refining pig-iron. 



310 



THE PUDDLING PROCESS. 



received in a separate mould; its composition may be generally expressed 
by the formula 2FeO. Si0 2 , the silica having been derived from the silicon 
contained in the cast-iron. 

The change effected in the composition of the iron by the process of 
refining will be apparent from the following table : — 



Refined Iron. 



Iron, . 

Carbon, 
Silicon, 
Sulphur, 



95-14 
3-07 
0-63 
0-16 



Phosphorus, 
Manganese, 
Slag, . 



0-73 

trace 
0-44 



The carbon, therefore, is not nearly so much diminished as the silicon, 
which is in some cases reduced to yVth of its former proportion by the 
refining process. Half of the sulphur is also sometimes removed, being 
found in the slag as sulphide of iron. The phosphorus is not removed to 
the same extent in the refining process, though some of it is converted 
into phosphoric acid, which may be found in the finery cinder. 

The further purification of the metal could not be effected in the 
refinery, since the fusibility of the iron is so greatly diminished as it 
approaches to a pure state, that it could not be retained in a fluid condi- 
tion at the temperature attainable in this furnace, and a more spacious 
hearth is required upon which the pasty metal may be kneaded into close 
contact with the oxide of iron which is to complete the oxidation and 
separation of the carbon. Tor this reason the metal is transferred to the 
puddling furnace. 

The puddling process is carried out in a reverberatory furnace (figs. 246, 
247) connected with a tall chimney provided with a damper, so as to admit 
of a very perfect regulation of the draught. A bridge of firebrick between 




Fig. 246. — Puddling furnace. 

the grate and the hearth prevents the contact of the coal with the iron to 
be puddled. The hearth is composed either of firebrick or of cast-iron 
plates, covered with a layer of very infusible slag, and cooled by a free 
circulation of air between them. This hearth is about 6 feet in length by 
4 feet in the widest part near the grate, and 2 feet at the opposite end; 
it is slightly inclined towards the end farthest from the grate, and finishes 
in a very considerable slope, at the lowest point of which is the floss-hole 



THE PUDDLING PROCESS. 



311 



for the removal of the slag. Since the metal is to attain a very high 
temperature in this furnace (estimated at 3000° F.), it is usually covered 
with an iron casing, so as to prevent any entrance of cold air through 
chinks in the brickwork. 

About 5 cwt. of the fine metal is broken up and heaped upon the 
hearth of this furnace, together with about 1 cwt. of iron scales (black 
oxide of iron, Fe 3 4 ), and of hammer-slag (basic silicate of iron, obtained 
in subsequent operations), which are added in order to assist in oxidising 
the impurities. When the metal has fused, the mass is well stirred or 



puddled, so that the oxide of iron may be 



brought 



into contact with 




Fig. 247. — Puddling furnace. 

every part of the metal, to effect the oxidation of the impurities. The 
metal now appears to boil, in consequence of the escape of carbonic oxide, 
and in about an hour from the commencement of the puddling, so much 
of the carbon has been removed that the fusibility of the metal is con- 
siderably diminished, and instead of retaining a fused condition at the 
temperature prevailing in the furnace, it assumes a granular, sandy or dry 
state, spongy masses of pure iron separating or coming to nature in the 
fused mass. The puddling of the iron is continued, until the whole has 
assumed this granular appearance, when the evolution of carbonic oxide 
ceases almost entirely, snowing that the removal of the carbon is nearly 
completed. The damper is now gradually raised so as to increase the 
temperature and soften the particles of iron, in order that they may be 
collected into a mass; and the more easily to effect this, a part of the 
slag is run off through the floss-hole. The workman then collects some 
of the iron upon the end of the paddle, and rolls it about on the hearth 
until he has collected a sort of rough ball of iron, weighing about half a 
hundredweight. When all the iron has been collected into balls in this 
way, they are placed in the hottest part of the furnace, and pressed occa- 
sionally with the paddle, so as to squeeze out a portion of the slag with 
which their interstices are filled. The doors are then closed to raise the 
interior of the furnace to a very high temperature, and after a short time, 
when the balls are sufficiently heated, they are removed from the furnace, 
and placed under a steam hammer, which squeezes out the liquid slag, 
and forces the softened particles of iron to cohere into a continuous oblong 
mass or bloom, w T hich is then passed betw r een rollers, by which it is ex- 
tended into bars. These bars, however {Rough or Puddled, or No. 1 Bar), 



312 



TAP-CINDER FROM PUDDLING FURNACE. 



are always hard and brittle, and are only fit for such, constructions as rail- 
way bars, where hardness is required rather than great tenacity. In order 
to improve this latter quality, the rough bars are cut up into short lengths, 
which are made into bundles, and after being raised to a high tempera- 
ture in the mill-furnace, are passed through rollers, which weld the 
several bars into one compound bar, ,to be subsequently passed through 
other rollers until it has acquired the desired dimensions. By thus fagot- 
ing or piling the bars, their texture is rendered far more uniform, and 
they are made to assume a fibrous structure, which greatly increases 
their strength {Merchant Bar, or No. 2 Bar). To obtain the best, or No. 
3 Beer, or wire-iron, these bars are doubled upon themselves, raised to a 
welding heat, and again passed between rollers. These repeated rollings 
have the effect of thoroughly squeezing out the slag which is mechanically 
entangled among the particles of iron in the rough bars, and would pro- 
duce flaws if allowed to remain in the metal. A slight improvement 
appears also to be effected in the chemical composition of the iron during 
the rolling, some of the carbon, silicon, phosphorus, and sulphur, still 
retained by the puddled iron, becoming oxidised, and passing away as 
carbonic oxide and slag. 

The following table exhibits the change in chemical composition which 
takes place in pig-iron when puddled (without previous refining) and 
rolled into wire-iron: — 



Effect of Puddling and Forging on Cast-iron. 



In 100 parts. 


Carbon. 


Silicon. 


Sulphur. 


Phosphorus. 


Grey pig-iron, 
Puddled bar, 
Wire-iron, . 


2-275 
0-296 
0-111 


2-720 
0-120 

0-088 


0*301 
0-134 
0-094 


0-645 
0-139 
0-117 



About 90 parts of bar-iron are obtained from 100 of refined iron by 
the puddling process, the difference representing the carbon which has 
passed off as carbonic oxide, and the silicon, sulphur, phosphorus, and 
iron, which have been removed in the slag or tap-cinder, this being 
essentially a silicate of protoxide and peroxide of iron, varying much in 
composition according to the character of the iron employed for puddling, 
and the proportions of iron-scale and hammer-slag introduced into the 
furnace. Of course, also, the material of which the hearth is composed 
will influence the composition of the slag. The following table affords 
an illustration of its percentage composition: — 



Protoxide of iron (FeO), 
Peroxide of iron (Fe 2 3 ), 
Silica, 
Phosphoric acid, 



Tap-Cinder from Puddling Furnace. 

Sulphide of iron, . 

Lime, . 

Oxide of manganese, 

Magnesia, 



57-67 
13-53 



7-29 



7-07 
4-70 
0-78 
0-26 



The lime in the above cinder was probably derived from the hearth 
of the furnace, which is sometimes lined with that material to assist in 
removing the sulphur. 

When pig-iron is puddled without undergoing the refining process, it 
becomes much more liquid than refined iron, and the process is some- 



THE BESSEMER PEOCESS. 



313 



times described as the pig-boiling process, whilst refined iron undergoes 
dry puddling. 

It will be observed that this process of puddling is attended with some 
important disadvantages; it involves a great expenditure of manual 
labour, and of a most exhausting kind; the very high temperature to 
which the puddler is exposed renders him liable to lung disease, and 
cataract is not uncommonly caused by the intense light from the glowing 
iron; the wear and tear of the puddling furnace is very considerable, and 
since it receives only ten or eleven charges of about 5 cwts. each in 
the course of twenty-four hours, it is necessary to work five or six 
puddling furnaces at once, in order to convert into bar-iron the whole of 
the cast-iron turned out from a single blast-furnace. These considera- 
tions have led to several attempts to improve the puddling process by 
employing revolving furnaces and other mechanical arrangements to 
supersede the heavy manual labour, and even to dispense with it 
altogether by forcing the air into the molten iron. The most generally 
known of the processes devised for this purpose is that of Bessemer, 
which consists in running the melted cast-iron into a huge crucible, and 
forcing air up through it under considerable pressure, thus combining the 
purifying influence of the blast of air 
in the refinery with the mechanical 
agitation effected in the puddling 
furnace. Bessemer's converting vessel 
(fig. 248) is a large, nearly cylindrical, 
crucible of wrought-iron, lined with 
ganister, having thirty or more open- 
ings of about Jth inch in diameter 
(A) at the bottom, through which air 
is blown at a pressure of 15 or 20 
lbs. upon the inch. This vessel is 
sometimes large enough to receive 10 
tons of cast-iron for a charge. The metal having been melted in a 
separate furnace, is run into the converting vessel, the blast being already 
turned on so that the liquid iron may not run into the air tubes. The 
iron burns vividly, and the oxide of iron produced is diffused in a melted 
state through the mass of metal by the rapid current of air. This oxide 
of iron acts upon the silicon and carbon in the cast-iron, converting the 
latter into carbonic oxide, which burns with flame at the mouth of the 
converter, and the former into silica, which enters into the slag, and is 
carried up as a froth to the surface of the liquid iron. The blast of air 
or blow is continued for about twenty minutes, when the disappearance 
of the flame of carbonic oxide indicates the completion of the process ; 
but the remaining purified iron is not pasty as in the puddling furnace, 
being retained in a perfectly liquid condition by the high temperature 
resulting from the combustion of part of the iron, so that the metal may 
be run out into moulds by tilting the converting vessel, which is usually 
hung upon trunnions. In this way about 85 parts of bar-iron are 
obtained from 100 of pig-iron. 

Although so great an economy of time and labour would result from 
the application of Bessemer's process, it has not superseded the puddling 
process, because it does not remove the sulphur and phosphorus from the 
pig-iron, so that only the best varieties of that material, extracted from 




Fig. 248. 



■Bessemer's converting 
vessel. 



314 



COMPOSITION OF BAR-IRON. 



haematite or magnetic ore, yield a bar -iron of good quality when purified 
in this way.* Moreover, the process is applicable only to grey iron rich 
in carbon and silicon, which is more expensive than the light forge irons 
treated in the puddling furnace. Its application to the manufacture of 
steel will be noticed hereafter. The effect of the Bessemer process upon 
a particular specimen of pig-iron is shown in the table : — 



In 100 parts of Pig-iron. 


Before. 


After. 


Carbon, . . . . . 

Silicon, 

Sulphur, .... 

Phosphorus .... 


3-309 
0-595 
0-485 
1-012 


0-218 
none 
0-402 
1-102 



In D dukes' rotating puddling furnace the pig-iron is run into a 
cylindrical chamber lined with a mixture of haematite and lime. Air is 
supplied by a fan, and the cylinder is revolved so as to bring the metal 
thoroughly into contact with the oxides of iron which form part of the 
charge, as in the ordinary puddling process. The charge of about 600 
lbs. is turned out in a single ball, which is further treated as usual. In 
Crampton's furnace a very high temperature is produced by a blast of air 
containing coal-dust in suspension. 

Composition of bar-iron.- — Even the best bar-iron contains from 0*1 to 
0*3 per cent, of carbon, together with minute proportions of silicon, 
sulphur, and phosphorus. Perfectly pure iron is inferior in hardness and 
tenacity to that which contains a small proportion of carbon. 

Bar-iron is liable to two important defects, which are technically known 
as cold-shortness and red-shortness. Cold-short iron is brittle at ordinary 
temperatures, and appears to owe this to the presence of phosphorus, of 
which element - 5 per cent, is sufficient materially to diminish the tenacity 
of the iron. When the iron is liable to brittleness at a red heat, it is 
termed red-short iron, and a very little sulphur is sufficient to affect the 
quality of the iron in this respect. 

There is much difference of opinion as to the true causes of the 
variation in the strength of wrought-iron, and this is not surprising when 
we reflect upon the number of circumstances which may be reasonably 
expected to exert some influence upon it. Not only the proportions 
of carbon, silicon, sulphur, phosphorus, and manganese may be supposed 
to affect the quality of the iron, but the state of combination in which 
these elements exist in the mass is not unlikely to cause a difference. 
It also appears certain that the mechanical structure, dependent upon 
the arrangement of the particles composing the mass of metal, has at 
least as much influence upon the tenacity of the iron as its chemical 
composition. 

The best bar-iron, if broken slowly, always exhibits a fibrous structure, 
the particles of iron being arranged in parallel lines. This appears to 
contribute greatly to the strength of the iron, for when it is wanting, and 
the bar is composed of a confused mass of crystals, it is weaker in pro- 
portion to the size of the crystals. The presence of phosphorus is said to 
favour the formation of large crystals, and hence to produce cold-shortness. 

* By lining the converter with basic bricks made by calcining a mixture of magnesian 
limestone and ferric oxide, the removal of phosphorus has been effected in the Bessemer 
process. 



MANUFACTURE OF STEEL. 



315 



There is some reason to believe that the fibrous is sometimes exchanged 
for the crystalline texture under the influence of frequent vibrations, 
as in the case of railway axles, girders of suspension-bridges, &c. 

Considering the difficult fusibility of bar-iron, it is fortunate that it 
possesses the property of being welded, that is, of being united by ham- 
mering when softened by heat. It is customary first to sprinkle the 
heated bars with sand or clay in order to convert the superficial oxide of 
iron into a liquid silicate, which will be forced out from between them by 
hammering or rolling, leaving the clean metallic surfaces to adhere. 



Manufacture of Steel. 

220. Steel differs from bar-iron in possessing the property of becoming 
very hard and brittle when heated to redness, and then suddenly cooled 
by being plunged into water. Perfectly pure iron, obtained by the 
electrotype process, is not hardened by sudden cooling ; but all bar-iron 
which contains carbon does exhibit this property in a greater or less 
degree according to the proportion of carbon present. It does not 
become decidedly steely, however, until the carbon amounts to 0*15 per- 
cent. The hardest steel contains about 1 *2 per cent, of carbon, and when 
the proportion reaches 1 *4 per cent, it begins to assume the properties of 
white cast-iron. Bar-iron may, therefore, be converted into steel by the 
addition of about 1 per cent, of carbon, and, conversely, cast-iron is 
converted into steel when the quantity of carbon contained in it is 
reduced to that amount.* There are thus two processes by which steel 
may be produced; but that which is employed almost exclusively in this 
country consists in combining bar-iron with the requisite amount of carbon 
by what is technically known as cementation, the bars being imbedded 
in charcoal and exposed for several days to a high temperature. 

The operation is effected in large chests of firebrick or stone, about 10 
or 12 feet long by 3 feet wide and 3 feet deep. 

Two of these chests are built into a dome-shaped furnace {converting 
furnace, fig. 249), so that the flame may circulate round them, and the 




Fig. 249. — Furnace for converting bar-iron into steel. 

furnace is surrounded with a conical jacket of brickwork in order to allow 
a steady temperature to be maintained in it for some days. The charcoal 

* Many metallurgists are of opinion that manganese has an influence similar to that of 
carbon in converting iron into steel. 



316 BLISTERED STEEL. 

is ground so as to pass through a sieve of J inch mesh, and spread in an 
even layer upon the bottom of the chests. Upon this the bars of iron, 
which must be of the best quality, are laid in regular order, a small 
interval being left between them, which is afterwards filled in with the 
charcoal powder, with a layer of which the bars are now covered; over 
this more bars are laid, then another layer of charcoal, and so on until the 
chest is filled. Each chest holds 5 or 6 tons of bars. One of the bars is 
allowed to project through an opening in the end of the chest, so that 
the workmen may withdraw it from time to time and judge of the progress 
of the operation. The whole is covered in with a layer of about 6 inches 
of damp clay or sand. 

The fire is carefully and gradually lighted, lest the chests should be 
split by too sudden application of heat, and the temperature is eventually 
raised to about the fusing-point of copper (2000° E.), at which it is main- 
tained for a period varying with the quality of steel which it is desired to 
obtain. Six or eight days suffice to produce steel of moderate hardness ; 
but the process is continued for three or four days longer if very hard 
steel be required. The fire is gradually extinguished, so that the chests 
are about ten days in cooling down. 

On opening the chests the bars are found to have suifered a remarkable 
change both in their external appearance and internal structure. They 
are covered with large blisters, obviously produced by some gaseous sub- 
stance raising the softened surface of the metal in its attempt to escape. 
It is conjectured that the blisters are caused by carbonic oxide produced 
by the action of the carbon upon particles of slag accidentally present 
in the bar. On breaking the bars across, the fracture is found to have 
a finely granular structure, instead of the fibrous appearance exhibited 
by bar-iron. Chemical analysis shows that the iron has combined with 
about 1 per cent, of carbon, and the most remarkable part of the result 
is that this carbon is not only found in the external layer of iron, which 
has been in direct contact with the heated charcoal, but is also present 
in the very centre of the bar. It is this transmission of the solid carbon 
through the solid mass of iron which is implied by the term cementation. 
The chemistry of the process probably consists in the formation of car- 
bonic oxide from the small quantity of atmospheric oxygen in the chest, 
and the removal of one-half of the carbon from this carbonic oxide, by 
the iron, which it converts into steel, leaving carbonic acid gas (2 CO — C 
= C0 2 ) to be reconverted into carbonic oxide by taking up more carbon 
from the charcoal (C0 2 + C = 2CO), which it transfers again to the iron. 
Experiment has shown that soft iron is capable of absorbing mechanically 
4*15 volumes of carbonic oxide at a low red heat, so' that the action of 
the gas upon the metal may occur throughout the substance of the bar. 
The carbonic oxide is retained unaltered by the iron after cooling, unless 
the bar is raised to the temperature required for the production of steel. 

The blistered steel obtained by this process is, as would be expected, 
far from uniform either in composition or in texture ; some portions of the 
bar contain more carbon than others, and the interior contains numerous 
cavities. In order to improve its quality it is subjected to a process of 
fagoting similar to that mentioned in the case of bar-iron ; the bars of 
blistered steel, being cut into short lengths, are made up into bundles, 
which are raised to a welding heat, and placed under a tilt-hammer, 
weighing about 2 cwt., which strikes two or three hundred blows in a 



HARDENING OF STEEL. 317 

minute ; in this way the several bars are consolidated into one compound 
bar, which is then extended under the hammer till of the required 
dimensions. The bars, before being hammered, are sprinkled with sand, 
which combines with the oxide of iron upon the surface, and forms 
a vitreous layer which protects the bar from further oxidation. The 
steel which has been thus hammered is much denser and more uniform 
in composition; its tenacity, malleability, and ductility are greatly in- 
creased, and it is fitted for the manufacture of shears, files, and other 
tools. It is commonly known as shear steel. Double shear steel is 
obtained by breaking the tilted bars in two, and welding these into a 
compound bar. 

The best variety of steel, however, which is perfectly homogeneous in 
composition, is that known as cad-steel, to obtain which about 30 lbs. of 
blistered steel are broken into fragments, and fused in a fireclay or plum- 
bago crucible, heated in a wind-furnace, the < surface of the metal being 
protected from oxidation by a little glass melted upon it. The fused 
steel is cast into ingots, several crucibles being emptied simultaneously 
into the same mould. Cast-steel is far superior in density and hardness 
to shear steel, but since it is exceedingly brittle at a red heat, great care 
is necessary in forging it. It has been found that the addition, to 100 
parts of the cast-steel, of one part of a mixture of charcoal and oxide of 
manganese, produces a fine-grained steel which admits of being cast on to 
a bar of wrought-iron in the ingot-mould, so that the tenacity of the latter 
may compensate for the brittleness of the steel when the compound bar 
is forged, the wrought-iron forming the back of the implement, and the 
steel its cutting edge. 

This addition of manganese to the cast-steel (Heath's patent) has effected 
a great reduction in its cost, allowing the use of blister steel made from 
British bar-iron, whereas, before its introduction, only the expensive iron 
of Swedish or Eussian make could be employed. But little manganese 
passes into the steel, the bulk of it going into the slag, and apparently 
carrying the sulphur and phosphorus with it. 

After the steel has been forged into the shape of any implement, it is 
hardened by being heated to redness, and suddenly chilled in cold water, 
or oil,* or mercury. It can thus be rendered nearly as hard as diamond, 
at the same time increasing slightly in volume (sp. gr. of cast-steel 7 '93 : 
after hardening, 7 "66). The chemical difference between hard and soft 
steel appears to be of the same kind as that between grey and white cast- 
iron (page 307), the greater proportion of the carbon in hard steel being in 
combination with the metal, while in soft steel the greater part seems to 
be in intimate mechanical admixture with the iron, for it is left undis- 
solved on treating the steel with an acid. If the hardened steel be heated 
to redness, and allowed to cool slowly, it is again converted into soft steel, 
but by heating it to a temperature short of a red heat, its hardness may 
be proportionally reduced. This is taken advantage of in annealing the 
steel or "letting it down" to the proper temper. The very hardest steel 
is almost as brittle as glass, and totally unfit for any ordinary use, but 
by heating it to a given temperature and allowing it to cool, its elasticity 
may be increased to the desired extent, without reducing its hardness 
below that required for the implement in hand. On heating a steel blade 

* Chilling in oil cools the steel less suddenly, on account of the lower specific heat of oil, 
and therefore does not render it so hard and brittle. It is often spoken qf as toughening. 



818 



TEMPERING OF STEEL. 



gradually over a flame, it will acquire a light yellow colour when its tem- 
perature reaches 430° F., from the formation of a thin film of oxide ; as 
the temperature rises the thickness of the film increases, and at 470° a 
decided yellow colour is seen, which assumes a brown shade at 490°, 
becomes purple at 520°, and blue at 550°. At a still higher temperature 
the film of oxide becomes so thick as to be black and opaque. Steel 
which has been heated to 430°, and allowed to cool slowly, is said to be 
tempered to the yellow, and is hard enough to take a very fine cutting 
edge, whilst, if tempered to the blue, at 550°, it is too soft to take a very 
keen edge, but has a very high degree of elasticity. The following table 
indicates the tempering heats for various implements : — 



Tempering of Steel. 



Temperature, F. 


Colour. 


Implements thus tempered. 


430° to 450° 


Straw-yellow. 


Razors, lancets. 


470° 


Yellow. 


Pen-knives. 


490° 


Brown-yellow. 


Large shears for cutting metal. 


510° 


Brown-purple. 


Clasp-knives. 


520° 


Purple. 


Table-knives. 


530° to 570° 


Blue. 


Watch-springs, sword-blades. 



If a knife blade be heated to redness its temper is spoilt, for it is con- 
verted into soft steel. 

In general, the steel implements are ground after being tempered, so 
that they are not seen of the colours mentioned above, except in the case. 
of watch springs. 

A steel blade may be easily distinguished from iron by placing a drop of 
diluted nitric acid upon it, when a dark stain is produced upon the steel, 
from the separation of the carbon. 

Some small instruments, such as keys, gun-locks, &c, which are 
exposed to considerable wear and tear by friction, and require the external 
hardness of steel without its brittleness, are forged from bar-iron, and 
converted externally into steel by the process of case-hardening, which 
consists in heating them in contact with some substance containing carbon 
(such as bone-dust, yellow prussiate of potash, &c), and afterwards chill- 
ing in water. A process which is the reverse of this is adopted in order 
to increase the tenacity of stirrups, bits, and similar articles made of cast- 
iron ; by heating them for some hours in contact with oxide of iron or 
manganese, their carbon and silicon are removed in the forms of carbonic 
oxide and silica, and they become converted into malleable cast-iron. 

The opinion that steel owes its properties entirely to the presence of 
carbon is not universally entertained. Some chemists believe that nitro- 
gen (or some analogous element) is an indispensable constituent, but the 
proportion of nitrogen found in steel is too minute to warrant this sup- 
position. Titanium is alleged by some authorities to have an important 
influence upon the quality of steel, but this also appears to be a doubtful 
matter. Bar-iron may be converted into steel by being kept at a high 
temperature in an atmosphere of coal gas, from which it abstracts carbon. 

Bessemer steel was originally produced by arresting the purification of 
cast-iron in Bessemer's process (page 313), as soon as the carbon had 
diminished to about 1 per cent., when the steel was poured out in the 



BESSEMER STEEL. 319 

fused state, i.e., in the form of cast-steel. A steel of better quality, 
however, has been obtained by continuing the purification until liquid 
bar-iron remains in the converter, and introducing the proper proportion 
of carbon in the form of a peculiar description of white cast-iron known 
as Spiegel-eisen (mirror iron), which crystallises in lustrous tabular crystals, 
and contains large proportions of carbon and manganese, being obtained 
by smelting spathic iron ore rich in manganese, with charcoal as fuel. 
The Spiegel-eisen is added, in a melted state, to the Bessemer iron before 
pouring from the converter. 

The composition of a sample of Spiegel-eisen smelted from a spathic ore, 
found near Miisen in Prussia, is here given : — 

Iron, . . . 82-86 I Silicon, . . . l'OO 

Manganese, . . 10*71 | Carbon, . . . 4*32 

Ferro-manganese, which is also employed in the manufacture of steel, 
is extracted from certain manganese ores, and contains about 74 per cent, 
of manganese, 5 per cent, of carbon, and 1 per cent, of silicon. Since the 
pig-iron obtained from clay ironstones is not well adapted for conversion 
into Bessemer steel, large quantities of haematite are imported for this 
manufacture from Bilbao (Spain), Elba, Algeria, &c. 

Siemens-Martin steel is made by melting together, in a Siemens' regene- 
rative furnace, pig-iron rich in manganese, and puddled iron, together with 
steel-scrap and ferromanganese, some magnetic iron ore being also some- 
times added as an oxidising agent to diminish the carbon. Samples of 
this steel were found to contain, in 100 parts — 

Carbon, .... 
Manganese, 

The soft variety was prepared for boiler-plates. 

Puddled steel is obtained by arresting the puddling process at an earlier 
stage than usual, so as to leave a proportion of carbon varying from 0*3 
to 1 *0 per cent. 

Natural steel or German steel results in a similar way, from the incom- 
plete purification of cast-iron in the refinery. The presence of manganese 
in the iron is favourable to its production. 

Krupp's cast-steel, manufactured at Essen near Cologne, and employed 
for ordnance, shells, &c, is a puddled steel made from haematite and 
spathic ore, smelted with coke. The iron thus obtained contains much 
manganese, which is removed in the puddling process. Krupp's steel 
contains about 1*2 per cent, of combined carbon, and is fused with a 
little bar-iron for casting ordnance. The fusion is effected in black lead 
crucibles holding 30 lbs. each, of which as many as 1200 are emptied 
simultaneously into the mould for the largest castings. A casting of 
1 6 tons requires about 400 men, who act together in well-disciplined gangs, 
so that the stream of molten metal shall flow continuously along the gut- 
ters into the mould. Such large castings must be allowed to cool very 
gradually, so that they are kept surrounded with hot cinders, sometimes 
for two or three months, till required for forging. 

221. Direct extraction of wrought-iron from the ore. — Where very rich 
and pure ores of iron, such as haematite and magnetic iron ore, are obtain- 
able, and fuel is abundant, the metal is sometimes extracted without 
being converted into cast-iron. It is probable that the iron of antiquity 



Tard. 


Medium. 


Soft. 


•67 


*35 


•16 


•40 


*18 


•14 



320 



EXTRACTION OF WROUGHT-IRON FROM THE ORE. 



was extracted in this way, for it is doubtful whether cast-iron was known 
to the ancients, and the slag left from old iron-works does not indicate 
the use of any flux. Some works of this description are still in operation 
in the Pyrenees, where the Catalan process is employed. The crucible is 
lined at the sides with thick iron plates, and at the bottom with a refrac- 
tory stone. A quantity of red hot charcoal is thrown into it, and the 
space above this is temporarily divided into two compartments by a 
shovel. The compartment nearest to the pipe through which the blast 
enters is charged with charcoal, and the other compartment with the 
calcined ore in small pieces. The shovel is then withdrawn, and a 
gradually increasing current of air supplied, fresh ore and fuel being added 
as they sink down. One part of the oxide of iron is reduced to the 
metallic state by the carbonic oxide, and the rest combines with the silica 
present in the ore to form a slag. After about five hours the spongy 




Fig. 250. — Catalan forge for smelting iron ores. 



masses of bar-iron are collected into a ball upon the end of an iron rod, 
and hammered into a compact mass like the metal obtained in the 
puddling furnace. The blowing machine employed in the Pyrenees is 
one in which the fall of water from a cistern down a long wooden pipe, 
sucks in, through lateral apertures, a supply of air which it carries down 
with it into a box, from which the pressure of the column of water 
projects it with some force through the blast-pipe, the water escaping 
from the box through another aperture. 

In the North American oloomery forges a modernised form of the same 
process is adopted. 



EXTRACTION OF IRON IN THE LABORATORY. 



321 




Fig. 251. — Sefstrbm furnace. 



The wrought-iron produced by this process always contains a larger 
proportion of carbon than puddled iron, and is therefore somewhat steely 
in character. 

222. Extraction of iron on the small scale. — In the laboratory, iron may be extracted 
from hflematite in the following manner : — A fireclay crucible (A, fig. 251), about 3 
inches high, is filled with charcoal powder, rammed down in successive layers ; a 
smooth conical cavity is scooped in the char- 
coal, and a mixture of 1 00 grs. red haematite, 
25 grs. chalk, and 25 grs. pipeclay, is intro- 
duced into it ; the mixture is covered with a 
layer of charcoal, and a lid placed on the 
crucible, which is heated in a Sefstrbm blast- 
furnace,* fed with coke in small pieces, for 
about half an hour. On breaking the cold 
crucible a button of cast-iron will be obtained. 

Nearly pure iron may be prepared by fusing 
the best wire-iron with about one-fifth of its 
weight of pure ferric oxide, to oxidise the 
carbon and silicon which it contains. Some 
powdered green glass, perfectly free from lead, must be employed as a flux, and the 
crucible (with its cover well cemented on with fireclay) exposed for an hour to a very 
high temperature. A silvery button of iron will then be obtained. 

223. Chemical properties of iron. — In its ordinary condition iron is 
unaffected by perfectly dry air, but in the presence of moisture and carbonic 
acid gas it is gradually converted into hydrated ferric oxide (2Fe 2 3 .3H 2 0) 
or rust. The water is decomposed, and ferrous carbonate formed 
(Fe + H 2 + C0 2 = FeC0 3 + H 9 ) ; this is dissolved by the carbonic acid 
present, and the solution rapidly absorbs oxygen from the air, deposit- 
ing the ferric oxide in a hydrated state, 2FeC0 3 + - Fe 2 3 + 2C0 2 . 
When iron nails are driven into a new oaken .fence, a black streak will 
soon be observed descending from each nail, caused by the formation of 
tannate of iron (ink) by the action of the tannic acid in the wood upon 
the solution of carbonate of iron formed from the nails. The diffusion of 
iron-mould stains through the fibre of wet linen by contact with a nail, is 
also caused by the formation of solution of carbonate of iron. The iron 
in chalybeate waters is also generally present in the form of carbonate 
dissolved in carbonic acid, and hence the rusty deposit which is formed 
when they are exposed to the air. Iron does not rust in water containing 
a free alkali, or alkaline earth, or an alkaline carbonate. 

Concentrated sulphuric and nitric acids do not act upon iron at the 
ordinary temperature, though they dissolve it rapidly when diluted. 
Even when boiling, strong sulphuric acid acts upon it but slowly. 
When iron has been immersed in strong nitric acid (sp. gr. 1*45), it is 
found to be unacted . upon when subsequent^' placed in diluted nitric 
acid, unless previously wiped; it is then said to have assumed the passive 
state. If iron wire be placed in nitric acid of sp. gr. 1*35, it is acted 
upon immediately, but if a piece of gold or platinum be made to touch it 
beneath the acid, the iron assumes the passive state, and the action 
ceases at once. A state similar to this, the cause of which has not yet 
been satisfactorily explained, is sometimes assumed by the other metals, 
though in a less marked degree. In the case of iron it has been attributed 



* This very useful furnace, shown in section in fig. 251, consists of two iron cylinders 
with a space (B) between them, into which air is forced through the tube C by a double- 
action bellows. The inner cylinder has a fireclay lining (D), through which four or six 
copper tubes (E) admit the blast into the fuel. 

X 



322 OXIDES OF IRON. 

to the formation of a coating of the magnetic oxide, which is sparingly 
soluble in strong nitric acid. 

224. Oxides of iron. — Three compounds of iron with oxygen are known 
in the separate state — 

Protoxide of iron, or ferrous oxide, . ' . . FeO 
Sesqui oxide or peroxide of iron, or ferric oxide, . Fe 2 3 

Magnetic oxide, or ferroso-ferric oxide, . . Fe 3 4 

Ferrous oxide is little known in the separate state on account of the 
readiness with which it absorbs oxygen and forms ferric oxide. If a 
little potash or ammonia be added to a solution of the green sulphate of 
iron (FeS0 4 ), a whitish precipitate of ferrous hydrate is formed, which 
immediately absorbs oxygen, and is converted into the dingy green 
ferroso-ferric hydrate; on exposing this to the air, it absorbs more 
oxygen and becomes brown ferric hydrate. This disposition of the 
ferrous hydrate to absorb oxygen is turned to advantage when a mixture 
of ferrous sulphate with lime or potash is employed for converting blue 
into white indigo. The ferrous oxide is a strong base. 

Peroxide or red oxide of iron has been already noticed among the ores 
of iron, and has also been referred to as occurring in commerce under the 
names of colcothar, jeweller's rouge, and Venetian red, which are obtained 
by the calcination of the green sulphate of iron ; 2FeS0 4 = Fe 2 3 + S0 2 
+ S0 3 . The hydrated peroxide (2Fe 2 3 .3H 2 0), obtained by decompos- 
ing a solution of ferric chloride with an alkali, forms a brown gelatinous 
precipitate, which is easily dissolved by acids ; but if it be dried and 
heated to dull redness, it exhibits a sudden glow, and is converted into a 
modification w r hich is dissolved with great difficulty by acids, although 
it has the same composition as the soluble form which has not been 
strongly heated. When the ferric oxide is heated to whiteness, it 
loses oxygen, and is converted into magnetic oxide of iron, 3Fe 2 3 
= 2Fe 3 4 + 0. Existing as it does in all soils, ferric oxide is believed to 
fulfil the purpose of oxidising the organic matter in the soil, and convert- 
ing its carbon into carbon dioxide, to be absorbed by the plant: the- 
ferric oxide being thus reduced to ferrous oxide, which is oxidised by the 
air, and fitted to perform again the same office. Ferric oxide, like alumina, 
is a weak base, and even exhibits some tendency to play the part of an 
acid towards strong bases, though not in so marked a degree as alumina. 

Magnetic or black oxide of iron is generally regarded as a compound of 
ferrous oxide with ferric oxide (FeO.Fe 2 3 ), a view which is confirmed 
by the occurrence of a number of minerals having the same crystalline 
form as the native magnetic oxide of iron, in which the iron, or part of 
it, is displaced by other metals. Thus, spinelle is MgO.Al 9 3 ; Frank- 
Unite, ZnO.Fe 2 3 ; chrome-iron ore, FeO.Cr 2 3 . The natural magnetic 
oxide was mentioned among the ores of iron, and this oxide has been 
seen to be the result of the action of air or steam upon iron at a high 
temperature. The hydrated magnetic oxide of iron (Fe 3 4 .H 2 0) is 
obtained as a black crystalline powder by mixing 1 molecule of ferrous 
sulphate with 1 molecule of ferric sulphate, and pouring the mixture 
into a slight excess of solution of ammonia, which is afterwards boiled 
with it. Magnetic oxide of iron, when acted upon by acids, yields mix- 
tures of ferrous and ferric salts, so that it is not an independent basic oxide. 



FEKRIO ACID. 323 

The very stable character of Fe 3 4 has led to its application for protect 
ing iron from rust. When superheated steam is passed over the red hoi 
metal, a very dense strongly adherent film of Fe 3 4 is produced, which 
effectually protects the metal (Barjfs process). A similar coating is pro- 
duced by the action of a mixture of air and carbonic acid gas (Bower's 
process). 

When iron filings are strongly heated with nitre, and the mass treated with a little 
water, a fine purple solution of potassium ferrate is obtained. A better method of 
preparing this salt consists in suspending 1 part of freshly precipitated ferric oxide 
in 50 parts of water, adding 30 parts of solid potassium hydrate, and passing chlorine 
till a slight effervescence commences; Fe 9 O3 + Cl 6 + 10KHO = 6KCl + 2(K. 2 FeO 4 ) 
+ 5H 2 ; the ferrate forms a black precipitate, being insoluble in the strongly alkaline 
solution, though it dissolves in pure water to form a purple solution, which is decom- 
posed even by dilution, oxygen escaping, and hydrated ferric oxide being precipi- 
tated. A similar decomposition takes place on boiling a strong solution, or on adding 
an acid with a view to liberate the ferric acid. The ferrates of barium, strontium, 
and calcium are obtained as fine red precipitates when solutions of their salts are 
mixed with potassium ferrate. 

225. Protosulphate of iron, copperas, green vitriol or ferrous sulphate, 
is easily obtained by heating 1 part of iron wire with 1 \ parts of strong 
sulphuric acid, mixed with 4 times its weight of water, until the whole 
of the metal is dissolved, when the solution is allowed to crystallise. Its 
manufacture on the large scale by the oxidation of iron pyrites has been 
already referred to. It forms fine green rhomboidal crystals, having the 
composition FeS0 4 .H 2 0.6Aq. 

The colour of the crystals varies somewhat, from the occasional presence 
of small quantities of ferric sulphate, Fe 2 (S0 4 ) 3 . It dissolves very easily 
in twice its weight of cold water, yielding a pale green solution. When 
the commercial sulphate of iron is boiled with water, it yields a brown 
muddy solution, in consequence of the decomposition of the ferric sulphate 
contained in it, with precipitation of a basic sulphate. Ferrous sulphate 
has a great tendency to absorb oxygen, and to become converted into 
ferric sulphate. Thus, the ordinary crystals when exposed to air gradually 
become brown, and are converted into a mixture of the normal and basic 
ferric sulphates. 

This disposition to absorb oxygen renders the ferrous sulphate useful 
as a reducing agent ; thus, it is employed for precipitating gold in the 
metallic state from its solutions. But its chief use is for the manufacture 
of ink and black dyes by its action upon vegetable infusions containing 
tannic acid, such as that of nut-galls. This application will be more 
particularly noticed hereafter. 

The salt FeS0 4 .S0 3 is obtained in minute prismatic crystals when a 
saturated solution of ferrous sulphate is added to an excess of strong 
sulphuric acid.* 

Sulphate of sesquioxide of iron, or persulphate of iron, or ferric sulphate, 
is found in Chili as a white silky crystalline mineral, coquimbite, having 
the composition Fe 2 (S0 4 ) 3 .9Aq. 

Ferrous and ferric phosphates are found associated in the mineral 
known as vivianite or native Prussian blue. 

226. Sesquichloride or perchloride of iron, or ferric chloride (Fe 2 Cl 6 ), 
is obtained in beautiful dark green crystalline scales when iron wire is 
heated in a glass tube through which a current of dry chlorine is passed, 

* Bolas, Journal of the Chemical Society, March 1874. 



324 FERRIC CHLORIDE. 

the ferric chloride passing off in vapour, and condensing in the cool part 
of the tube. The crystals almost instantly become wet when exposed to 
air on account of their great attraction for water. Ferric chloride may be 
obtained in solution by dissolving iron in hydrochloric acid, and convert- 
ing the ferrous chloride (FeCl 2 ) thus formed into ferric chloride by the 
action of nitric and hydrochloric acids (page 172). A strong solution 
yields crystals of Fe 2 Cl 6 .2Aq. The solution of ferric chloride has been 
recommended in some cases as a disinfectant, being easily reduced to 
ferrous chloride, and thus affording chlorine to unstable organic matters 
(page 156 ). In contact with paper, Fe 2 Cl 6 becomes reduced to FeCl 2 when 
exposed to light. A solution of perchloride of iron in alcohol is used in 
medicine under the name of tincture of iron. 

Solution of ferric chloride is capable of dissolving a very large quantity of pure 
freshly precipitated ferric oxide, nine niolcules of Fe 2 3 being dissolved by one 
molecule of Fe. 2 Cl 6 . The solution of ferric oxy chloride thus obtained has a very dark 
red colour, and yields a very copious brown precipitate with common water, or any 
solution containing even a trace of a sulphate. By dialysis, an aqueous solution of 
ferric oxide is left in the dialyser. 

227. Atomic weight of iron. — When iron is dissolved in hydrochloric 
acid, 28 parts by weight of iron combine with 35*5 parts of chlorine, 
displacing 1 part of hydrogen. The specific heat of iron and its isomor- 
phism with magnesium, zinc, and cadmium, show that its atomic weight 
must be represented by 56, so that iron is a diatomic or bivalent element, 
one atom of iron being exchangeable for two atoms of hydrogen. 

The molecular formula of ferric chloride has been confirmed by the 
determination of the specific gravity of its vapour, which has been found 
to be 165 times that of hydrogen. If, therefore, one volume (or one 
atom) of hydrogen be represented as having a weight = 1, two volumes 
(or one molecule) of ferric chloride vapour would weigh (165x2) 330, 
a number nearly agreeing with the sum of two atoms of iron (112) and 
six atoms of chlorine (213 - 0). 

It will be remarked that iron possesses a different atomicity accordingly 
as it exists in ferrous or ferric compounds. Thus, in ferrous oxide (FeO) 
and ferrous chloride (FeCl 2 ), it occupies the place of two atoms of hydrogen,- 
and is diatomic ; but in ferric oxide (Fe 2 B ) and ferric chloride (Fe 2 Cl 6 ) 
each atom of iron occupies the place of three atoms of hydrogen, and is 
triatomic. 

Some chemists designate the diatomic iron existing in ferrous compounds by the 
name ferrosum (Fe"), and the triatomic iron of the ferric compounds by ferricum 
(Fe'"). Others regard iron as a tetratomic metal Fe iv , existing in the ferrous salts as 
a group of two atoms united by two bonds, and in the ferric salts as a group of two 
atoms united by one bond. On this view, ferrous chloride would be Fe 2 Cl 4 , or 
Cl 2 :=:Fe=:Fe=Cl 2 and ferric chloride would be Fe a Cl 6 , or Cl 3 =Fe— Fe=Cl 3 . 

COBALT. 

Co" = 59 parts b}^ weight. 

228. Some of the compounds of cobalt are of considerable importance 
in the arts, on account of their brilliant and permanent colours. It is 
generally found in combination with arsenic and sulphur, forming tin- 
white cobalt, CoAs 2 , and cobalt glance, CoAs 2 .CoS 2 , but its ores also gene- 
rally contain nickel, copper, iron, manganese, and bismuth. 

The metal itself is obtained by strongly heating the cobalt oxalate 



COBALT. 325 

(CoC 2 4 ) in a covered porcelain crucible. In its properties it closely 
resembles iron, but it is said to surpass it in tenacity. 

Two oxides of cobalt are known — the protoxide or eobaltous oxide, 
CoO, which, is decidedly basic, and the sesquioxide or cobaltic oxide, 
Co 2 3 , which is a very feeble base. The protoxide of cobalt, like those 
of iron and manganese, tends to absorb oxygen from the air, and when 
heated in the air, becomes converted into CoO.Co 2 3 , corresponding to 
the magnetic oxide of iron. The commercial oxide of cobalt, which is 
employed for painting on porcelain, is obtained by roasting the ore, in 
order to expel part of the sulphur and arsenic, dissolving it in hydro- 
chloric acid, and precipitating the sesquioxide of iron by the careful 
addition of lime, when the remaining arsenic is also precipitated as ferric 
arseniate. Hydrosulphuric acid is passed through the acid solution to 
precipitate the bismuth and copper, leaving the cobalt and nickel in 
solution. The latter, having been boiled to expel the excess of hydro- 
sulphuric acid, is neutralised with lime and mixed with solution of 
chloride of lime, which precipitates the sesquioxide of cobalt as a black 
powder, leaving the oxide of nickel in solution, from which it may be 
precipitated by the addition of lime. 

The salts of cobalt have a fine red colour in the hydrated state, or in 
solution, but are generally blue when anhydrous. The cobalt silicate 
associated with potassium silicate forms the blue colour known as smalt, 
which is prepared by roasting the cobalt ore, so as to convert the bulk of 
the cobalt into oxide, leaving, however, a considerable quantity of arsenic 
and sulphur still in the ore. The residue is then fused in a crucible with 
ground quartz and carbonate of potash, when a blue glass is formed, con- 
taining cobalt silicate and potassium silicate, • whilst the iron, nickel, 
and copper, combined with arsenic and sulphur, collect at the bottom of 
the crucible and form a fused mass of metallic appearance known as 
speiss, which is employed as a source of nickeL The blue glass is poured 
into cold water, so that it may be more easily reduced to the fine powder 
in which the smalt is sold. If the cobalt ore destined for smalt be over- 
roasted, so as to convert the iron into oxide, this will pass into the smalt 
as a silicate, injuring its colour. 

Zaffre is prepared by roasting a mixture of cobalt ore with two or three 
parts of sand. 

Tlienard's blue consists of cobalt phosphate and aluminium phosphate, 
and is prepared by mixing precipitated alumina with cobalt phosphate 
and calcining in a covered crucible. The phosphate is obtained by 
precipitating a solution of cobalt nitrate with phosphate of potassium or 
sodium. 

RinmarHs green is prepared by calcining the precipitate produced by 
sodium carbonate in a mixture of cobalt sulphate with zinc sulphate. It 
is a compound of the oxides of cobalt and zinc. 

Cobaltous chloride (CoCl 2 ), obtained by dissolving eobaltous oxide in 
hydrochloric acid, forms red hydrated crystals, which become blue when 
part of their water is expelled. If strong hydrochloric acid be added to 
a red solution of this salt, it becomes blue ; if enough water be now added 
to render it pink, the blue colour may be produced at pleasure by boiling, 
the solution first passing through a neutral tint. Chloride of cobalt is 
employed as a sympathetic ink, for characters written with its pink solu- 
tion are nearly invisible till they are held before the fire, when they 



326 COMPOUNDS OF NICKEL. 

become blue, and resume their original pink colour if exposed to the air : 
a little chloride of iron causes a green colour. 

The cobaltous sulphide (CoS) is obtained as a black precipitate when 
an alkaline sulphide is added to a solution of a salt of cobalt. A cobaltic 
sulphide (Co 2 S 3 ) is found in grey octahedra, forming cobalt pyrites. The 
disidphide (CoS 2 ) has been obtained artificially. 

When ammonia in excess is added to a solution of a salt of cobalt, a 
deep red liquid is produced, which rapidly absorbs oxygen from the air, 
especially if ammonium chloride be present, giving rise to the production 
of some remarkable and complex bases which contain the elements of 
ammonia and of different oxides of cobalt. 

NICKEL. 

Ni" = 59 parts by weight. 

229. Nickel owes its value in the useful arts chiefly to its property of 
imparting a white colour to the alloys of cupper and zinc, with which it 
forms the alloy known as German silver. Nickel is very nearly allied to 
cobalt, and generally occurs associated with that metal in its ores. One 
of the principal ores of nickel is the Kupfernickel or copper-nickel, so 
called by the German miners because they frequently mistook it for an 
ore of copper ; it has a reddish metallic appearance, and the formula 
NiAs. 'Grey nickel ore or nickel glance is an arseniosulphide of nickel, 
NiAs 2 .NiS 2 . Arseniccd nickel, NiAs 2 , corresponds to tin- white cobalt. 
The metal is commonly extracted from the speiss separated during the 
preparation of smalt from cobalt ores (page 325); the oxide of nickel 
prepared by the method described above, when strongly heated in contact 
with charcoal, yields metallic nickel containing carbon. 

Nickel is now extracted from an ore found in New Caledonia, which 
contains silicates of nickel, iron, &c. The ore is treated with sulphuric 
acid, and the solution mixed with ammonium sulphate. On evaporation, 
nickel ammonium sulphate is deposited in crystals, which are purified by 
recrystallisation and boiled with an alkaline oxalate. The precipitated 
nickel oxalate is decomposed by boiling with sodium carbonate, producing 
sodium oxalate which may be used again, and nickel carbonate which is 
reduced by charcoal. 

The pure metal is obtained by igniting the oxalate, as in the case of 
cobalt, which it much resembles in properties. 

The oxides of nickel correspond in composition to those of cobalt. The 
salts formed by nickelous oxide (NiO) are usually green, and give bright 
green solutions. The hydrate has a characteristic apple green colour, and 
does not absorb oxygen from the air like the cobaltous hydrate. The 
greater facility with which the latter is converted into sesquioxide has 
been applied (as above described) to effect the separation of the two 
metals. Nickelous oxide has been found native in octahedral crystals, 
which have also been obtained accidentally in a copper-smelting furnace. 

Nickel sulphate (NiS0 4 .H 2 0.6Aq.) forms fine green prismatic crystals, 
the water of constitution" in which may be displaced by potassium 
sulphate, forming the doidrte sulphate of nickel and potassium, NiSG 4 . 
K 2 S0 4 .6Aq., which crystallises so readily that it was at one time the 
form in which nickel was separated from the other metals present in its 
ores. 



MANGANESE. 327 

Three sulphides of nickel are known — a subsulphide, Ni 2 S ; a proto- 
sulphide, MS, found native as capillary pyrites, and obtained as a black 
precipitate by the action of an alkaline sulphide upon a salt of nickel ; 
and a disidphide, NiS 2 . 

MANGANESE. 

Ma" = 55 parts by weight. 

230. Manganese much resembles iron in several particulars relating both 
to its physical and chemical characters, and is often found associated, 
in small quantities, with the compounds of that metal. The metal itself 
has not been applied to any useful purpose. 

It is obtained by reducing manganous carbonate (MnC0 3 ) with char- 
coal, at a very high temperature, when a fused mass, composed of man- 
ganese combined with a little carbon (corresponding to cast-iron), is 
obtained, which is freed from carbon by a second fusion in contact with 
manganous carbonate. 

Metallic manganese is darker in colour than pure iron, and very much 
harder; it is brittle, and only feebly attracted by the magnet. It is 
somewhat more easily oxidised than iron. 

231. Oxides of manganese. — Three distinct compounds of manganese 
with oxygen are known — 

Protoxide of manganese, or manganous oxide, . . MnO 

Sesquioxide, or manganic oxide, .... Mn 2 3 

Peroxide, or manganese dioxide, . . . . Mn0 2 

The peroxide of manganese is the chief form in which this metal is found 
in nature, and is the source from which all other compounds of manganese 
are obtained. Its chief mineral form is pyrolusite, which forms steel- 
grey prismatic crystals ; but it is also found amorphous, as psilomelane, 
and in the hydrated state as wad. In commerce pyrolusite is known as 
black manganese, or simply manganese, and is largely imported from 
Germany, Spain, &c, for the use of the manufacturer of bleaching-powder 
and the glass-maker. It is also used as a cheap source of oxygen, which 
it evolves when heated to redness, leaving the red oxide of manganese, 
Mn 3 4 . The manganese dioxide is an indifferent oxide, and does not 
combine with acids ; when heated with strong sulphuric acid, it loses half 
its oxygen, and forms the manganous oxide, which is a powerful base, 
and reacts with the sulphuric acid to form manganous sulphate ; Mn0 2 
-f H 2 S0 4 = MnS0 4 + H 2 + O. Since the natural dioxide contains ferric 
oxide, some ferric sulphate is formed at the same time ; but if the mixture 
be dried and heated to redness, the ferric salt is decomposed, leaving ferric 
oxide, while the manganous sulphate is not decomposed, and may be 
dissolved out of the mass by treatment with water. On evaporating the 
solution, and allowing it to cool, it deposits light pink crystals of sulphate 
of manganese, MnS0 4 H 2 0.4Aq. 

This salt is employed by the dyer and calico-printer in the production 
of black and brown colours. When a solution of manganous sulphate is 
mixed with solution of chloride of lime (page 155), it gives a black pre- 
cipitate of hydrated peroxide of manganese — 

2MnS0 4 + Ca(C10) 2 + 2CaO = 2Mn0. 2 + 2CaS0 4 + CaCl 2 . 



328 oxides or manganese. 

By decomposing a solution of manganous sulphate with potash or soda, 
a white precipitate of manganous hydrate is obtained, which becomes 
brown when exposed to the air, absorbing oxygen, and becoming con- 
verted into manganic hydrate. 

If solution of manganous sulphate be mixed with sodium carbonate, 
a white precipitate of manganous carbonate, 2MnC0 3 .H 2 0, is obtained. 
The pink crystallised mineral manganese spar consists of manganous 
carbonate (MnC0 3 ). 

Protoxide of manganese or manganous oxide (MnO) itself is obtained as 
a green powder by heating manganous carbonate in a tube through which 
hydrogen is passed to exclude the air, which would convert the protoxide 
into red oxide (Mn 3 4 ). The protoxide has been obtained in transparent 
emerald-green crystals. 

Sesquioxid,e of manganese or manganic oxide, crystallised in octahedra, 
forms the mineral braunite, and, in combination with water, the prismatic 
crystals of manganite (Mn 2 3 .H 2 0), which often occurs in the commercial 
ores of manganese. The manganic oxide is a weak base, dissolving in 
acids to form deep red solutions, which evolve oxygen when heated, 
leaving manganous salts. The manganic sulphate combines with potas- 
sium sulphate to form manganese alum, KMn(S0 4 ) 2 .12Aq., corresponding 
in crystalline form, as in composition, to aluminium alum. When 
manganese dioxide in minute quantity is added to melted glass, it imparts 
a purple colour, which is probably due to the formation of a manganic 
silicate. The amethyst is believed by some to owe its colour to the same 
cause. 

Red oxide of manganese (Mn 3 4 ) is the most stable of the oxides of this 
metal, and is formed when either of the others is heated in air. Thus 
obtained, it has a brown or reddish colour; but it is found in nature as 
the black mineral hausmannite. In composition it resembles the magnetic 
oxide of iron, but it seems probable that its true formula is 2MnO.Mn0 2 , 
for when treated with diluted nitric acid it leaves the black hydrated 
dioxide. 

When a compound containing manganese, in however small quantity, is fused 
on a piece of platinum foil with sodium carbonate (page 114), a mass of sodium 
manganate (Na 2 Mn0 4 ) is formed, which is green while hot, and becomes blue on 
cooling. The oxygen required to convert the lower oxides of manganese into the 
manganate has been absorbed from the air. 

Potassium manganate is obtained by mixing finely-powdered manganese 
dioxide into a paste with an equal weight of potassium hydrate dissolved 
in a little water, drying the paste, and heating it to dull redness in a glass 
tube, through which oxygen is passed as long as it is absorbed. When 
the mass is treated with a little cold water, it gives a dark emerald green 
solution, and by evaporating this over oil of vitriol, in vacuo, dark green 
crystals of potassium manganate (K 2 Mn0 4 ) are formed, which have the 
same crystalline form as those of potassium sulphate. These crystals 
dissolve unchanged in water containing potash; but when dissolved in 
pure water they yield a red solution of potassium permanganate, and a 
precipitate of manganese dioxide — 

3K 2 Mn0 4 + 2H 2 = K 2 Mn 2 8 + Mn0 2 + 4KHO . 

The change is more completely effected by adding a little free acid, even 
carbonic acid. The changes of colour thus produced have acquired 



PERMANGANATE OF POTASH. 329 

for the manganate the name chameleon mineral. The solution of 
potassium manganate (containing free potash) is very easily decomposed 
by substances having an attraction for oxygen. Thus, most organic sub- 
stances abstract oxygen from it, and cause the separation of brown man- 
ganic oxide; Filtering its solution through paper will even effect this 
change. The offensive emanations from putrefying organic matters are at 
once oxidised and rendered inodorous by manganates. 

Sodium manganate (Na 2 Mn0 4 ) obtained by heating manganese dioxide 
with sodium hydrate, under free exposure to air, is employed in a state 
of solution in water, as Condy's green disinfecting fluid. It is also used 
as a bleaching agent, and in the preparation of oxygen at a cheap rate. 
Barium manganate forms the pigment known as Cassel green. 

Permanganic acid, H. 2 Mn 2 8 , has been obtained in a hydrated crystalline state 
by decomposing the barium permanganate with sulphuric acid, and evaporating 
the solution in vacuo. It is a brown substance, easily dissolving in water to a red 
liquid, which is decomposed at about 90° F., evolving oxygen, and depositing 
manganese dioxide. 

When potassium permanganate is added to oil of vitriol + a molecule of water, red 
oily drops separate, which explode when heated ; but, with care, they may be distilled 
off at about 60° C. . in violet vapours, which condense into a very dark liquid which 
immediately sets lire to combustible bodies. This is probably H 2 Mn 2 8 , of which the 
crystalline body above mentioned is a combination with water. 

Permanganate of potash or potassium permanganate (K 2 Mn 2 8 ) is 
largely used in many chemical operations. In order to prepare it, 4 parts 
of finely -powdered manganese dioxide are intimately mixed with 3 J parts 
of potassium chlorate, and 5 parts of potassium hydrate dissolved in a 
very little water. The pasty mass is dried, and heated to dull redness 
for some time in an iron tray or earthen crucible. The potassium chlorate 
imparts the required oxygen. On treating the cold mass with water, 
potassium manganate is dissolved, forming a dark green solution. This 
is diluted with water, and a stream of carbonic acid gas passed through 
it as long as any change of colour is observed; 3K 2 Mn0 4 + 2C0 2 
= K 2 Mn 2 8 + Mn0 2 + 2K 2 C0 3 . The precipitated Mn0 2 is allowed to 
settle, and the clear red solution poured off and evaporated to a small 
bulk. On cooling, it deposits prismatic crystals of the permanganate 
(K 2 Mn 2 8 ), which are red by transmitted light, but reflect a dark green 
colour. The potassium carbonate, being much more soluble in water, is 
left in the solution. Potassium permanganate is remarkable for its great 
colouring power, a very small quantity of the salt producing an intense 
purplish-red colour in a large quantity of water. Its solution in water is 
very easily decomposed and bleached by substances having an attraction 
for oxygen, such as sulphurous acid or a ferrous salt. If a very small 
piece of iron wire be dissolved in diluted sulphuric acid, the solution of 
ferrous sulphate so produced will decolorise a large volume of weak 
solution of the permanganate, being converted into ferric sulphate — 
K 2 Mn 2 8 + 10FeSO 4 + 8H 2 S0 4 = K 2 S0 4 + 2MnS0 4 + 5Fe 2 (S0 4 ) 3 + 8H 2 0. 

This decomposition forms the basis of a valuable method for determining 
the proportion of iron in its ores. 

Many organic substances are easily oxidised by potassium permanganate, 
and this is the case especially with the offensive emanations from putres- 
cent organic matter. Hence it is extensively used under the name of 
Condy's red disinfecting fluid \ in cases where a solid or liquid substance is 
to be deodorised. 



330 CHLORIDES OF MANGANESE. 

An alkaline solution of the permanganate is sometimes used as an 
oxidising agent, since it parts with oxygen when boiled, becoming green 
from the production of manganate ; K 2 Mn 2 8 4- 2KHO = 2K 2 Mn0 4 
+ H 2 + 0. 

232. Chlorides of manyanese. — There appear to be three compounds of 
manganese with chlorine, corresponding to three of the oxides, viz., 
MnCl 2 , Mn 2 Cl 6 , and MnCl 4 ; but only the first is obtainable in the pure 
state, the others forming solutions which are easily decomposed with 
evolution of chlorine. 

The manganous chloride (MnCl 2 ) is obtained in large quantity as a waste product 
in the preparation of chlorine, for the manufacture of bleaching-powder. Since there 
is no useful application for it, the manufacturer sometimes reconverts it into the black 
oxide. As the native binoxide always contains iron, the liquor obtained by treating 
it with hydrochloric acid contains ferric chloride (Fe 2 Cl 6 ) mixed with chloride of 
manganese (MnCl 2 ). In order to separate the iron, advantage is taken of the circum- 
stance that sesquioxides are weaker bases than the protoxides, so that if a small pro- 
portion of lime be added to the solution, the iron may be precipitated as sesquioxide, 
without decomposing the chloride of manganese; Fe 2 Cl 6 + 3CaO = Fe 2 3 + 3CaCl. 2 . 
The solution of chloride of manganese is then mixed with chalk, and subjected to the 
action of steam at a pressure of about two atmospheres. Carbonate of manganese is 
precipitated (MnCl 2 + CaC0 3 = CaCl 2 + MnC0 3 ), and when this is dried and heated to 
about 600° F. in a current of moist air, carbonic acid gas is expelled, and a large pro- 
portion of the oxide of manganese is converted into binoxide, which may be employed 
again for the preparation of chlorine. 

According to Weldon's process (page 148), the iron is precipitated as peroxide by 
adding chalk, which leaves the manganese in solution ; an excess of lime is then 
added and air blown through the mixture at about 150° F., when the white precipi- 
tate of MnO, formed at first, absorbs the oxygen, and becomes a black compound of 
Mn0 2 with lime, which is used over again for the preparation of chlorine. Unless 
the lime is added in excess, only MnO.Mn0. 2 is formed, so that the excess of lime 
displaces the MnO and allows it to be converted into Mn0 2 . In another process 
Weldon employs magnesia instead of lime, with the view of afterwards recovering the 
chlorine from the chloride of magnesium, in the form of hydrochloric acid (see page 
283), and using the magnesia over again. 

By dissolving potassium permanganate in oil of vitriol, and adding fragments of 
fused sodium chloride, a remarkable greenish-yellow gas is obtained, which gives 
purple fumes with moist air, and is decomposed by water, yielding a red solution which 
contains hydrochloric and permanganic acids. It, therefore, must contain manganese 
and chlorine, and is sometimes regarded as the perchloride (MnCl 7 ) ; but it is more 
probably an oxy chloride of manganese (see Chlorochromic acid). Care is required in 
its preparation, which is sometimes attended with explosion. 



CHKOMIUM. 

Cr= 52 '5 parts by weight. 
233. This metal derives its name from xpto/xa, colour, in allusion to the 
varied colours of its compounds, upon which their uses in the arts chiefly 
depend. It is comparatively seldom met with, its principal ore being the 
chrome-iron ore (FeO.Cr 2 3 ), which is remarkable for its resistance to the 
action of acids and other chemical agents. It is chiefly found in the 
Shetland Islands, Sweden, Russia, and the United States, and is imported 
for the manufacture of bichromate of potash (K 2 0.2Cr0 3 ), which is one of 
the chief commercial compounds of chromium. The ore is first heated to 
redness and thrown into water, in order that it may be easily ground to 
a fine powder, which is mixed with carbonate of potash, chalk being 
added to prevent the fusion of the mass, and strongly heated in a current 
of air on the hearth of a reverberatory furnace, the mass being occasionally 



CHEOMIC ACID. 331 

stirred to expose a fresh surface to the air. The oxide of iron is thus 
converted into sesquioxide, and the sesquioxide of chromium (Cr 2 3 ) also 
absorbs oxygen from the air, becoming chromic acid (CrO s ), which com- 
bines with the potash to form chromate of potash (K 2 0.Cr0 3 ). Mtre is 
sometimes added to hasten the oxidation. On treating the mass with 
water, a yellow solution of chromate of potash is obtained, which is drawn 
off from the insoluble residue of sesquioxide of iron and lime, and mixed 
with a slight excess of nitric acid — 

2(K 2 O.Cr0 8 ) + 2HN0 3 = K 2 0.2Cr0 3 + 2KNO s + H 2 . 

Chromate of Bichromate of 

potash. potash. 

The solution, when evaporated, deposits beautiful red tabular crystals of 
bichromate of potash (potassium dichromate) which dissolve in 10 parts of 
cold water, forming an acid solution. It is from this salt that the other 
compounds of chromium are immediately derived. 

Metallic chromium has received no useful application. It has been 
obtained in octahedral crystals by the action of sodium on chromic 
chloride, and in a pulverulent state by the action of potassium. In 
the latter condition it is easily acted on by acids, but the crystallised 
chromium is insoluble even in nitrohydrochloric acid. Like aluminium, 
it is more easily attacked by hydrated alkalies at a high temperature, 
evolving hydrogen and producing chromates. It is remarkably infusible. 

234. Oxides of Chromium. — Two oxides of chromium are known in 
the separate state — the sesquioxide or chromic oxide, Cr 2 3 , and chromic 
anhydride, Cr0 3 . Protoxide of chromium or chromous oxide (CrO) is 
known in the hydrated state, and perchromic -acid (H 2 Cr 2 8 ) is believed 
to exist in solution. 

Chromic anhydride (commonly called chromic acid), the most important 
of these, is obtained by adding to one measure of a solution of bichromate 
of potash, saturated at 130° F., one measure and a half of concentrated 
sulphuric acid, by small portions at a time, and allowing the solution to 
cool, when chromic anhydride crystallises out in fine crimson needles, 
which are deliquescent, very soluble in water, and decomposed by a 
moderate heat into oxygen and chromic oxide. Chromic anhydride is a 
powerful oxidising agent; most organic substances, even paper, will reduce 
it to the green chromic oxide. A mixture of potassium dichromate and 
sulphuric acid is employed for bleaching some oils, the colouring matter 
being oxidised at the expense of the chromic acid, and chromic sulphate 
produced — 

K 2 Cr 2 7 + 4H 2 S0 4 = K 2 S0 4 + Cr 2 (S0 4 ) 3 + o 3 + 4H 2 ■ 

The dichromate itself evolves oxygen when heated to bright redness, being 
first fused, and afterwards decomposed; 2K 2 Cr 2 r = 2K 2 Cr0 4 + Cr 9 3 
4- 3 . The oxidising effect of the potassium dichromate, under the action 
of light, upon gelatine and albumen, receives very important applications 
in photography. 

Chromate of potash or normal potassium chromate (K 2 O.Cr0 3 or K 2 Cr0 4 ), 
is formed by adding carbonate of potash to the red solution of bichromate 
of potash until its red colour is changed to a fine yellow, when it is 
evaporated and allowed to crystallise. It forms yellow prismatic crystals 
having the same form as those of potassium sulphate, and is far more 



332 CHROMATES. 

soluble in water than the dichromate, yielding an alkaline solution. It 
becomes red when heated, and fuses without decomposition. Potassium 
chromate has been found in some yellow samples of saltpetre from 
Chili. 

Tercliromate of potash (K 2 0.3Cr0 3 ) has been obtained in red crystals 
by adding nitric acid to the dichromate. 

It will be observed that the chromates of potassium are rather excep- 
tional salts. The yellow or normal chromate, K 2 Cr0 4 , is formed upon 
the model of imaginary chromic acid, H 2 Cr0 4 . The red chromate or 
potassium dichromate is not a true acid salt, for it contains no hydrogen; 
it is sometimes called anhydro- chromate, and written K 2 Cr0 4 .Cr0 3 . The 
terchromate would be K 2 Cr0 4 .2Cr0 3 . 

Chrome-yellow is the chromate of lead (PbCr0 4 ), prepared by mixing 
dilute solutions of lead acetate and potassium chromate. It is largely 
used in painting and calico-printing, and by the chemist as a source of 
oxygen for the analysis of organic substances, since, when heated, it 
fuses to a brown mass, which evolves oxygen at a red heat. Chrome- 
yellow being a poisonous salt, its occasional use for colouring confectionery 
is very objectionable. Chromate of lead in prismatic crystals forms the 
rather rare red lead ore of Siberia, in which chromium was first 
discovered. 

Orange chrome is a basic chromate of lead (PbCr0 4 .PbO), and may be 
obtained by boiling the yellow chromate with lime; 2(PbCr0 4 ) + CaO 
= PbCr0 4 .PbO -t- CaCr0 4 . The calico-printer dyes the stuff with yellow 
chromate of lead, and converts it into orange chromate by a bath of lime- 
water. 

The colour of the ruby (crystallised alumina) appears to be due to the 
presence of a small proportion of chromic anhydride. 

Sesquioxide of chromium or chromic oxide CCr 2 3 ) is valuable as a green 
colour, especially for glass and porcelain, since it is not decomposed by 
heat. Being extremely hard, it is used in making razor-strops. It is 
prepared by heating bichromate of potash with one-fourth of its weight 
of starch, the carbon of which deprives the chromic acid of half its oxygen, 
leaving a mixture of chromic oxide with potassium carbonate, which may 
be removed by washing with water. If sulphur be substituted for the 
starch, potassium sulphate will be formed, which may also be removed by 
water. When chromic oxide is strongly heated, it exhibits a sudden 
glow, becomes darker in colour, and insoluble in acids which previously 
dissolved it easily ; in this respect it resembles alumina and ferric oxide. 
Like these oxides, the chromic oxide is a feeble base ; it is remarkable 
for forming two classes of salts, having the same composition, but differing 
in the colour of their solutions, and in some other properties. Thus, 
there are two modifications of the chromic sulphate — the green sulphate, 
Cr 2 (S0 4 ) 3 .5Aq., and the violet sulphate, Cr 2 (S0 4 ) 3 .15Aq. The solution 
of the latter becomes green when boiled, being converted into the former. 
Chrome ahem forms dark purple octahedra (KCr'"(S0 4 ) 2 .12Aq.) which 
contain the violet modification of the sulphate ; and if its solution in 
water be boiled, its purple- colour changes to green, and the solution 
refuses to crystallise.* The anhydrous chromic sulphate forms red 
crystals, which are insoluble in water and acids. A green basic chromic 
borate is used in painting and calico-printing, under the name of vert 
* Exposure to cold, it is said, again converts it into the crystallisable violet form. 



CHLORIDES OF CHROMIUM. 333 

de Guignet, and is prepared by strongly heating bichromate of potash 
with 3 parts of crystallised boracic acid, when potassium borate and 
chromic borate are formed, half the oxygen of the Cr0 3 being expelled. 
The potassium borate and the excess of B 2 3 are afterwards washed 
out by water. By reducing an alkaline chromate with sodium thio- 
sulphate, the compound Cr. 2 3 .Cr0 3 has been obtained as a brown pre- 
cipitate. 

Protoxide of chromium or chromous oxide (CrO) is not known in the 
pure state, but is precipitated as a brown hydrate when chromous chloride 
is decomposed by potash. It absorbs oxygen even more readily than 
ferrous oxide, becoming converted in (CrO.Cr 2 3 ) corresponding in com- 
position to the magnetic oxide of iron. Chromous oxide is a feeble base ; 
a double sulphate (K 2 Cr"(S0 4 ) 2 .6Aq.) is known, which has the same 
crystalline form as the corresponding iron salt (K 2 Fe"(S0 4 ) 2 .6Aq.) ; it 
has a blue colour, and gives a blue solution, which becomes green when 
exposed to air, from the formation of chromic oxide. 

Perchromic acid (H 2 Cr 2 8 ) is believed to exist in the blue solution 
obtained by the action of hydric peroxide upon solution of chromic acid, 
but neither the acid nor its salts have been obtained in a separate state. 

235. Chlorides of chromium. — The chromic chloride (Cr 2 Cl 6 ) obtained by passing 
dry chlorine over a mixture of chromic oxide with charcoal, heated to redness in a 
glass tube, is converted into vapour, and condenses upon the cooler part of the tube 
in shining leaflets having a fine violet colour. Cold water does not affect them, but 
boiling water slowly dissolves them to a green solution resembling that obtained by 
dissolving chromic oxide in hydrochloric acid. 

Chromous chloride (CrCl 2 ) results from the action of hydrogen, at a red heat, upon 
chromic chloride. Strange to say, it is white, and dissolves in water to form a blue 
solution, which absorbs oxygen from the air, becoming green. It is remarkable that 
if the violet chromic chloride is suspended in water, and a minute quantity of chromous 
chloride added, the former immediately dissolves to a green solution, evolving heat. 

The so-called chlorochromic acid (CrO.X'l 2 ) is a very remarkable brown-red liquid, 
obtained by distilling 10 parts of common salt and 17 of bichromate of potash, 
previously fused together and broken into fragments, with 40 parts of oil of vitriol — 

K 2 Cr 2 7 + 4XaCl + 3H 2 S0 4 = K 2 S0 4 + 2Xa 2 S0 4 + 3H 2 + 2Cr0 2 Cl 2 . 

It much resembles bromine in appearance, and fumes very strongly in air, the mois- 
ture of which decomposes its red vapour, forming chromic and hydrochloric acids ; 
CrO.,Cl 2 + 2H 2 = H. 2 Cr0 4 + 2HCl. It is a very powerful oxidising and chlorinating 
agent, and inflames ammonia and alcohol when brought in contact with them. 

It is occasionally used to illustrate the nature of illuminating flames; for if 
hydrogen be passed through a bottle containing a few drops of chlorochromic acid, 
the gas becomes chai'ged w r ith its vapour, and, if kindled, burns with a brilliant 
white flame, which deposits a beautiful green film of chromic oxide upon a cold 
surface. 

The name chromic oxy chloride, applied to this compound, is more correct than 
chlorochromic acid, for it is not known to form salts. When chlorochromic acid is 
heated, in a sealed tube, to 370° F., it is converted into a black solid body according 
to the equation 3Cr0 2 Cl 2 = Cl 4 + CrCl 2 .2Cr0 3 . 

Chromic fluoride (CrF 6 ) is another volatile compound of chromium obtained 
by distilling chromate of lead with fluor spar and sulphuric acid ; it is a red gas, con- 
densibleto a red liquid at a low temperature. "Water decomposes it, yielding chromic 
and hydrofluoric acids. 

Chromic sulphide (Cr 2 S 3 ) is formed when vapour of carbon disulphide is passed 
over chromic oxide heated to redness. It forms black lustrous scales resembling 
graphite. 

By fusing chromic hydrate with sodium carbonate and sulphur, sodium sulpho- 
chromite Xa 2 Cr 2 S 4 is obtained, as a dark red body insoluble in water, and not easily 
attacked by hydrochloric or sulphuric acid. Sulphochromites of other metals have 
also been obtained. 



334 MOLYBDENUM. 

236. General review of iron, cobalt, nickel, ?nanganese, and chromium. — 
Many points of resemblance will have been noticed in the chemical 
history of these metals. They are all capable of decomposing water at 
a red heat, and easily displace hydrogen from hydrochloric acid. Each 
of them forms a base by combining with one atom of oxygen, and these 
oxides produce salts which have the same crystalline form. All these 
oxides, except that of nickel, easily absorb oxygen from the air, and are 
converted into sesquioxides. The sesquoxide of nickel is an indifferent 
oxide, while that of cobalt is very feebly basic ; the sesquioxide of 
manganese is a stronger base, and the basic properties of the sesquioxides 
of chromium and iron are very decided. Nickel does not exhibit any 
tendency to form a well-marked acid oxide, but the existence of an acid 
oxide of cobalt is suspected ; and iron, manganese, and chromium form 
undoubted acid oxides with three atoms of oxygen. Nickel is only known 
to form one compound with chlorine ; cobalt and manganese form, in addi- 
tion to their protochlorides, very unstable perchlorides known only in 
solution, but iron and chromium form very stable volatile perchlorides. 
The metals composing this group are all diatomic,* and are found associated 
in natural minerals ; this is especially the case with iron, manganese, 
cobalt, and nickel. They are all attracted by the magnet, and require a 
very high temperature for their fusion. Iron and chromium connect this 
group with aluminium, their sesquioxides being isomorphous with alumina, 
and their perchlorides volatile like aluminium chloride. 

237. Molybdenum (Mo = 96) derives its name from /xoAvpSaiva, lead, on account 
of the resemblance of its chief ore, molybdena, to black lead. Molybdena is the 
molybdenum disulphide (MoS 2 ), and is found chiefly in Bohemia and Sweden; it may 
be recognised by its remarkable similarity to plumbago, and by its giving a blue 
solution when boiled with strong sulphuric acid. It is chiefly employed for the pre- 
paration of ammonium molybdate, which is used in testing for phosphoric acid. For 
this purpose the disulphide is roasted in air at a dull red heat, when S0. 2 is evolved, 
and molybdic anhydride (Mo0 3 ) mixed with oxide of iron is left. The residue is 
digested with strong ammonia, which dissolves the former as ammonium molybdate, 
obtainable in prismatic crystals (NH 4 HMo0 4 ) on evaporation. When a solution of 
ammonium molybdate is added to a phosphate dissolved in diluted nitric acid, a 
yellow precipitate of ammonium phosphomolybdate is produced, which contains 
molybdic and phosphoric acids combined with ammonia, by the formation of which 
very minute quantities of phosphoric acid can be detected. If hydrochloric acid be 
added in small quantity to a strong solution of molybdate of ammonium, the molybdic 
acid is precipitated, but it is dissolved by an excess of hydrochloric acid, and if the 
solution be dialysed, the molybdic acid is obtained in the form of an aqueous solution 
which reddens blue litmus, has an astringent taste, and leaves a soluble gum-like 
residue when evaporated. Molybdic anhydride fuses at a red heat to a yellow glass, 
and may be sublimed in a current of air in shining needles. In contact with diluted 
hydrochloric acid and metallic zinc, it is converted into a blue compound of the com- 
position (Mo0 2 .4Mo0 3 ) which is soluble in water, but is precipitated on adding a 
saline solution. Molybdate of lead (PbMo0 4 ) is found as a yellow crystalline mineral. 
The molybdic oxide (Mo0 2 ) is basic, and forms dark red-brown salts. Molybdous oxide 
(MoO) is obtained by adding an alkali to the solution resulting from the prolonged 
action of zinc upon a hydrochloric solution of molybdic acid. It is a basic oxide which 
absorbs oxygen from the air. 

Metallic molybdenum is obtained by reducing molybdic acid with charcoal at a 
white heat, as a white metal, fusible with difficulty, unacted upon by hydrochloric 
and diluted sulphuric acids, but converted into molybdic acid by boiling with nitric 
acid. It is rather a light metal, its specific gravity being 8 '62. When heated in 
chlorine it yields molybdenum tetrachloride (MoCl 4 ), which forms a red vapour, and 
condenses in crystals resembling iodine, soluble in water. A dichloridc (MoCl 2 ) is 

* Chromium, like iron, is triatomic in the sesquioxides and the compounds derived from 
it and in chromic acid it must be regarded as hexatomic. 



VANADIUM. 335 

also known. The trisulphide (MoS 3 ) and tctrasulphide (MoSJ of molybdenum are 
soluble in alkaline sulphides. 

In addition to the natural sources of molybdenum above mentioned, there may be 
noticed molybdic ochre (an impure molybdic acid), and the difficultly fusible masses 
called bear, from the copper works in Saxony, which contain a large amount of 
molybdenum combined with iron, copper, cobalt, and nickel. Molybdenum has been 
detected in the mud deposited by the Buxton thermal water. 

238. Vanadium* (V = 51'3) was originally discovered in certain Swedish iron 
ores, but its chief ore is the vanadiate of lead, which is found in Scotland, Mexico, 
and Chili. Vanadic acid has also been found in some clays, in the cupriferous sand- 
stone at Perm in Russia, and Alderley Edge in Cheshire. By treating the vanadiate 
of lead with nitric acid, expelling the excess of acid by evaporation, and washing 
out the lead nitrate with water, impure vanadic anhydride (V.,0 5 ) is obtained, which 
may be purified by dissolving in ammonia, crystallising the vanadiate of ammonium, 
and decomposing it by heat, when vanadic anhydride is left as a reddish-yellow fusible 
solid which crystallises on cooling, and dissolves sparingly in water, giving a yellow 
solution. It dissolves in hydrochloric acid, and if the solution be treated with a reduc- 
ing agent (such as hydrosulphuric acid) it assumes a fine blue colour. If a solution 
of ammonium vanadiate be mixed with tincture of galls, it gives an intensely black 
fluid, which forms an excellent ink, for it is not bleached by acids (which turn it 
blue), alkalies, or chlorine. 

Vanadium itself has been obtained by heating its chloride in hydrogen, as a 
silvery white metal. Berzelius endeavoured to procure it by heating vanadic acid 
with potassium, but Roscoe, who has carefully investigated the vanadium com- 
pounds, has shown that the apparentlv metallic powder thus obtained is really an 
oxide (V 2 2 ). 

239. The oxides of vanadium correspond in composition to those of nitrogen. 
V 2 2 is a basic oxide, forming salts which give lavender-coloured solutions ; these 
absorb oxygen rapidly from the air, and act as powerful reducing agents. V 2 3 is a 
black crystalline body resembling plumbago, and capable of conducting electricity, 
obtained by heating vanadic anhydride in a current of hydrogen ; it is a basic oxide. 
V. 2 4 is produced when V 2 3 is heated in air ; it also plays the part of a base, 
yielding blue salts. Vanadic anhydride, V 2 5 , forms purple and green compounds 
with the above oxides. Metavanadic acid, HV0 3 , crystallises in beautiful golden 
scales. The yellow fuming liquid formerlv called chloride of vanadium is really an 
oxychloride, VOCl 3 . The oxychlorides, V 2 2 C1, VOC1, and VOCl 2 , have also been 
obtained. There are two compounds of vanadium with nitrogen, V"N" and VN 2 . 
It will be remarked that the composition of the compounds of vanadium connects 
this metal with nitrogen, phosphorus, and arsenic. Compounds of vanadium are 
now used for blacks in calico-printing, in conjunction with chlorates and aniliue 
hydrochlorate. 

BISMUTH. 

Bi"'r=210 parts by weight. 

240. Bismuth, though useful in various forms of combination, is too 
brittle to be employed in the pure metallic state. It is readily distin- 
guished from other metals by its peculiar reddish lustre and its highly 
crystalline structure, which is very perceptible upon a freshly broken 
surface ; large cubical (or, strictly speaking, rhombohedral) crystals of 
bismuth are easily obtained by melting a few ounces in a crucible^ allow- 
ing it to cool till a crust has formed upon the surface, and pouring out 
the portion which has not yet solidified, when the crystals are found 
lining the interior of the crucible. It is somewhat lighter than lead (sp. 
gr. 9*8), and volatilises more readily at high temperatures. 

Unlike most other metals, bismuth is found chiefly in the metallic 

state, disseminated, in veins, through gneiss and clay-slate. The chief 

supply is derived from the mines of Schneeberg, in Saxony, where it is 

associated with the ores of cobalt. Native bismuth, together with the 

* Vanadis, a Scandinavian deity. 



336 



BISMUTH. 




Fig. 252. — Extraction of bismuth. 



oxides and sulphides, are found abundantly in Bolivia, accompanied by 
tin-stone and sometimes by silver and gold. 

In order to extract the metal from the masses of earthy matter through 
which it is distributed, advantage is taken of its verv low f using-point 

(507° F.). The ore is 
broken into small pieces, 
and introduced into iron 
cylinders which are fixed 
in an inclined position 
over a furnace (fig. 252). 
The upper opening of the 
cylinders, through which 
the ore is introduced, is 
provided with an iron 
door, and the lower open- 
ing is closed with a plate 
of firebrick perforated for 
the escape of the metal, 
which flows out, when the cylinders are heated, into iron receiving pots, 
which are kept hot by a charcoal fire. 

Commercial bismuth generally contains considerable quantities of 
arsenic, sulphur, and silver ; it is sometimes cupelled in the same manner 
as lead, in order to extract the silver, the oxide of bismuth being after- 
wards again reduced to the metallic state by heating it with charcoal. 
Pure bismuth dissolves entirely and easily in diluted nitric acid (sp. gr. 
1*2); but if it contains arsenic, a white deposit of bismuth arseniate is 
obtained. Hydrochloric and diluted sulphuric acids will not act upon 
bismuth. 

The chief use of bismuth is in the preparation of certain alloys with 
other metals. Some kinds of type metal and stereotype metal contain 
bismuth, which confers upon them the property of expanding in the 
mould during solidification, so that they are forced into the finest lines 
of the impression. 

This metal is also remarkable for its tendency to lower the fusing-point 
of alloys, which cannot be accounted for merely by referring to the low 
fusing-point of the metal itself. Thus, an alloy of 2 parts bismuth, 
1 part lead, and 1 part tin, fuses below the temperature of boiling water, 
although the most fusible of the three metals, tin, requires a temperature 
of 442° F. An alloy of this kind is used for soldering pewter. Bismuth 
is also employed, together with antimony, in the construction of thermo- 
electric piles. 

241. Oxides of bismuth. — Three compounds of bismuth with oxygen have been 
prepared ; bismuthous oxide BiO, bismuthic oxide Bi 2 3 , and bismuthic anhydride 
Bi,0 5 . 

Bismuthous oxide (BiO) is obtained as a black precipitate by reducing bismuthic 
chloride with stannous chloride in the presence of an excess of potash. It is easily 
converted into bismuthic oxide when heated in contact with air. 

Bismuthic oxide (Bi 2 3 ) is the basic and most important oxide of the metal. It 
is formed when bismuth is heated in air, or when bismuth nitrate is decomposed by 
heat, and is a yellow powder which becomes brown when heated, and fuses easily. 
Bismuthic oxide forms the rare mineral bismuth-ochre. 

Bismuthic anhydride (Bi 2 5 ) is formed Avhen bismuthic oxide is suspended in a 
strong solution of potash through which chlorine is passed, when a brown substance 
is formed which, when treated with warm strong nitric acid, yields bismuthic acid 



OXIDES OF BISMUTH. 337 

(HBi0 3 ) as a red powder, which, becomes brown at 120° C, losing H 2 and becoming 
Bi 2 O s . When further heated, this loses and becomes Bi 2 4 , or Bi 2 3 .Bi 2 5 . 
When heated with acids it also evolves oxygen, and forms salts of bismuthic oxide. 
The bismuthates of the alkali metals are very unstable, being decomposed by water. 

242. The only two salts of bismuth which are known in the arts are 
the basic nitrate (trisnitrate of bismuth or flake-white) and the oxychloride 
of bismuth (pearl-white). The preparation of these compounds illustrates 
one of the characteristic properties of the salts of bismuth, viz., the 
facility with which they are decomposed by water with the production of 
insoluble basic salts. 

If bismuth be dissolved in nitric acid, it acquires oxygen from the 
latter, and becomes bismuthic oxide, which reacts with nitric acid to form 
the bismuthic nitrate Bi(N0 3 ) 3 , and this may be obtained in prismatic 
crystals containing 5Aq. If the solution be mixed with a large quantity 
of water, it deposits a precipitate of fake-white, Bi(N0 3 ) 3 .2Bi(OH) 3 , or 
basic nitrate of bismuth, the remainder of the nitric acid being left in the 
solution. 

Pearl white has the composition 2(BiCl 3 .Bi 2 3 ).H 2 0, and is obtained by 
dissolving bismuth in nitric acid, and pouring the solution into water in 
which common salt has been dissolved. 

Bismuthite, which is, next to native bismuth, the most important of the bismuth 
ores, is composed of 3Bi 2 3 .C0 2 .H 2 0. 

Bismuthic chloride (BiCl 3 ) may be distilled over when bismuth is heated in a current 
of dry chlorine ; it is a deliquescent fusible solid, easily dissolved by hydrochloric 
acid, but decomposed by water, with formation of the above-mentioned oxychloride of 
bismuth; 3BiCl 3 + 3H 2 6= BiCl 3 .Bi 2 3 + 6HC1. This compound is so insoluble in 
water that nearly every trace of bismuth may be precipitated from a moderately acid 
solution of the trichloride by adding much water. 

Bismuthous sulphide (BiS) is sometimes found in nature, but more frequently 
bismuthic sulphide (Bi 2 S 3 ) or bismuth glance, Avhich occurs in dark grey lustrous prisms 
isomorphous with native sulphide of antimony. It is also obtained as a black pre- 
cipitate by the action of hydrosulphuric acid upon bismuthic salts. Bismuthic sul- 
phide is not soluble in diluted sulphuric or hydrochloric acid, but dissolves easily in 
nitric acid. Bolivite is an oxysulphide, Bi 2 S 3 .Bi 2 3 . 

ANTIMONY. 

Sb"'=120 parts by weight. 

243. Antimony is nearly allied to bismuth in both its physical and 
chemical characters. It is even harder and more brittle than that metal, 
being easily reduced to a black powder. Its highly crystalline structure 
is another very well-marked feature, and is at once perceived upon the 
surface of an ingot of antimony, where it is exhibited in beautiful fern- 
like markings (star antimony). Its crystals belong to the same system 
(the rhombohedral) as those of bismuth and arsenic. It is much lighter 
than bismuth (sp. gr. 6*715), and requires a higher temperature (800° F.) 
to fuse it, though it is more easily converted into vapour, so that, when 
strongly heated in air, it emits a thick white smoke, the vapour being 
oxidised. Like bismuth, it is but little affected by hydrochloric or dilute 
sulphuric acid, but nitric acid oxidises it, though it dissolves very little 
of the metal, the greater part being left in the form of antimonic acid. 
The best mode of dissolving antimony is to boil it with hydrochloric acid 
and to add nitric acid by degrees. 

Antimony is chiefly found in nature as grey antimony ore or sulphide 
of antimony (Sb 2 S 3 ), which occurs in Cornwall, but much more abun- 

Y 



338 ANTIMONY. 

dantly in Hungary. It is found in veins associated with galena, iron 
pyrites, quartz, and heavy spar. In order to purify it from these, advan- 
tage is taken of its easy fusibility, the ore being heated upon the hearth 
of a reverberatory furnace, with some charcoal to prevent oxidation, when 
the sulphide of antimony melts and collects below the impurities, whence 
it is run off and cast into moulds. The product thus obtained is known 
in commerce as crude antimony, and contains sulphides of arsenic, iron, 
and lead. 

To obtain regulus of antimony or metallic antimony, the sulphide of 
antimony is sometimes fused in contact with refuse metallic iron (such as 
the clippings of tin-plate), when sulphide of iron is formed, and collects 
as a fused slag upon the surface of the melted antimony Sb 2 S 3 + Fe 3 
= 3FeS + Sb. 2 . The antimony thus obtained always contains a consider- 
able proportion of iron. 

A purer product is procured by another process, which consists in 
roasting the sulphide in a reverberatory furnace at a temperature insuffi- 
cient to fuse it, for about twelve hours, when most of the sulphur and 
arsenic are expelled as sulphurous and arsenious oxides, carrying with 
them a considerable quantity of oxide of antimony. The roasted ore 
has a brown-red colour, and contains both oxide and sulphide of antimony : 
it is mixed into a paste with i its weight of charcoal saturated with a 
strong solution of carbonate of soda. The mixture is strongly heated in 
crucibles, when the oxide of antimony is reduced by the charcoal, and a 
portion of the sulphide, having been converted into oxide by double 
decomposition with the sodium carbonate (Sb 2 S 3 + 3Na 2 C0 3 = Sb 2 3 
+ 3Na 2 S + 3C0 2 ), is also reduced, the remainder of the sulphide com- 
bining with the sodium sulphide to form a slag which floats above the 
metallic antimony; the latter is cast into ingots for the market, and the 
slag, known as crocus of antimony (chiefly 3]STa 2 S.Sb 2 S 3 ), is employed for 
the preparation of some of the compounds of the metal. 

On the small scale, antimony may be extracted from the sulphide by fusing it in 
an earthen crucible with 4 parts of commercial potassium cyanide, at a moderate 
heat ; or by mixing 4 parts of the sulphide with 3 of bitartrate of potash and 1| of 
nitre, and throwing the mixture, by small portions, into a red hot crucible, when . 
the sulphur is oxidised, and converted into potassium sulphate,' by the nitre, which is 
not present in sufficient quantity to oxidise the antimony, so that the metal collects 
at the bottom of the crucible. 

The brittleness of antimony renders it useless in the metallic state 
except for the construction of thermo-electric piles, where it is employed 
in conjunction with bismuth, Antimony is employed, however, to 
harden several useful alloys, such as type-metal, shrapnel-shell bullets, 
Britannia metal, and pewter. 

Amoiyhous antimony. — The ordinary crystalline form of antimony may be obtained, 
like copper and other metals, by decomposing solutions containing the metal by 
transmitting the galvanic current (the solution should not .contain more than 7 per 
cent, of antimonious chloride) ; but in some cases the antimony is deposited from 
very strong solutions in an amorphous condition, having properties very different 
from those of ordinary antimony. The best mode of obtaining it in this form is to 
decompose a solution of 1 part of tartar emetic (tartrate of antimony and potassium) in 
4 parts of a strong solution of antimony trichloride (obtained by heating hydrochloric 
acid with antimony sulphide till it refuses to dissolve any more), by the aid of three 
cells of Smee's battery, the zinc of which is connected by a copper wire with a plate 
of copper immersed in the antimonial solution, whilst the platinised silver of the 
battery is connected with a plate of antimony in the same solution, at some little 



OXIDES OF ANTIMONY. 339 

distance from the copper plate. The deposit of antimony which forms upon the 
copper has a brilliant metallic appearance, but is amorphous, and not crystalline, 
like the ordinary metal. If it be gently heated or sharply struck, its temperature 
rises suddenly to about 400°, and it becomes converted into a form more nearly 
resembling crystalline antimony. At the same time, however, thick fumes of 
antimony trichloride are evolved, for this substance is always present in the 
amorphous antimony to the amount of 5 or 6 per cent.,* so that, as yet, there is not 
sufficient evidence to establish beyond a doubt the existence of a pure amorphous 
form of antimony corresponding to amorphous phosphorus, however probable this 
may appear from the chemical resemblance between these elements. 

244. Oxides of antimony. — There are two well-known oxides of anti- 
mony, the sesquioxide (Sb 2 3 ) and antimonic oxide (Sb 2 5 ). Teroxide 
or sesquioxide of antimony, or antimonious oxide, is formed when anti- 
mony burns in air, and is prepared on a large scale by roasting either 
the metal or the sulphide in air, for use in painting as a substitute 
for white lead. It is also found in nature as white antimony ore or 
valentinite. Antimonious oxide forms a crystalline powder, usually com- 
posed of minute prisms having the shape of the rarer form of arsenious 
oxide (page 246), whilst occasionally it is obtained in crystals similar to 
those of the common octahedral arsenious oxide, with which, therefore, 
antimonious oxide is isodimoiylwus. The octahedral form appears 
to be produced only when the prismatic form is slowly sublimed in 
a non-oxidising atmosphere. The mineral exitete is prismatic oxide of 
antimony,, and senarmontite is the octahedral form of that oxide. When 
heated in air the oxide assumes a yellow colour, afterwards takes fire, 
smoulders, and becomes converted into the antimonious antimoniate 
(Sb 2 3 .Sb 2 5 = Sb 2 4 ), which was formerly regarded as an independent 
oxide. The sesquioxide is insoluble in water, but acids dissolve it, 
forming salts, though its basic properties are weak, and its salts rather 
ill defined. Potash and soda are also capable of dissolving it, whence it 
is sometimes called antimonious anhydride, corresponding to nitrous anhy- 
dride. Two crystallised antimonites of sodium have been obtained, the 
neutral antimonite XaSb0 2 . 6Aq., and the terantimoniteXaSb0 2 .Sb 2 3 . Aq. ; 
the former is sparingly soluble, the latter almost insoluble in water. 

Antimonic oxide (Sb 2 5 ) is formed when antimony is oxidised with 
nitric acid; it then forms a white powder, which should be well washed 
and dried. When heated it becomes pale yellow, and is decomposed at 
a high temperature, leaving Sb 2 3 .Sb 2 5 . It is dissolved by solution of 
potash, forming potassium antimoniate. Antimonic acid HSb0 3 , corre- 
sponding to nitric acid, is obtained by decomposing antimonic chloride 
with water; SbCl 5 + 3H 2 = HSb0 3 + 5HC1. 

Antimonic hydrate, dried over sulphuric acid, is Sb 5 .3H 2 0. At 
100° C. it becomes Sb 2 5 .2H 2 0. At about 200°, it is Sb 2 5 .H 2 0. These 
may be represented, respectively, as H 3 Sb0 4 , H 4 Sb 2 6 r , and HSb0 3 , 
corresponding to ortho-, pyro- and metaphosphoric acids. 

Potassium antimoniate is made by gradually adding 1 part of powdered 
antimony to 4 parts of nitre fused in a clay crucible. The mass is 
powdered and washed with warm water to remove the excess of nitre and 
the potassium nitrite, when the anhydrous potassium antimoniate is left; 
and on boiling this for an hour or two with water, it becomes hydrated 

* It has been plausibly suggested that the sudden rise of temperature may be due to 
the presence of an antimony compound analogous to the so-called chloride of nitrogen, the 
latter element being connected with antimony by several chemical analogies. 



340 ANTIMONIETTED HYDROGEN. 

and dissolves. The solution, when evaporated, leaves a gummy mass of 
potassium antimoniate, having the composition 2KSb0 3 .5Aq. 

When the solution of potassium antimoniate is treated with carbonic 
acid gas, a crystalline precipitate of biantimoniate (2KSb0 3 .Sb 2 5 ) is 
obtained. If the antimoniate be fused (in a silver crucible) with potassium 
hydrate, it becomes converted into metantimoniate (K 4 Sb 2 7 ), which is 
decomposed by water into potash and oimetantimoniate (K 2 H 2 Sb 2 7 ), 
which may be crystallised from the solution. This latter salt is valuable 
as a test for soda, since the sodium bimetantimoniate, Na H 2 Sb 2 7 , is 
one of the very few salts of sodium which are insoluble in water, and is 
therefore obtained as a crystalline precipitate when the potassium bimet- 
antimoniate is added to a solution containing sodium. The solution of 
potassium bimetantimoniate is gradually changed by keeping, into anti- 
moniate, which does not so readily precipitate sodium, K 9 H 2 Sb 9 0- 
= 2KSb0 3 + H 2 0. 

It will be remarked that the antimoniates correspond in composition 
with the metaphosphates, whilst the metantimoniates represent the pyro- 
phosphates. 

Naples yellow is a compound of antimonic oxide with lead oxide. 

245. Antimonietted. 'hydrogen (SbH 3 ) is obtained, mixed with free 
hydrogen, when an alloy of zinc and antimony is acted on by diluted sul- 
phuric acid, or when a solution of a salt of antimony (tartar emetic, for 
example) is poured into a hydrogen apparatus containing zinc and dilute 
sulphuric acid (fig. 253). If the gas be inflamed as it issues into the air, 
it burns with a livid flame, emitting fumes of antimonic oxide, and when 
a piece of glass or porcelain is depressed in the flame (fig. 254) it becomes 
coated with a black film of metallic antimony. A red heat decomposes 
the gas into its elements, so that if the tube through which it is passing 
be heated with a spirit-lamp (fig. 255), a lustrous black deposit of anti- 




Fig. 253. 




Fig. 255. 
Fig. 254. . ° 

mony will be formed just beyond the heated part. The composition of 
antimonietted hydrogen is not certainly established, since it has never 
been obtained unmixed with hydrogen; but it is believed to contain 
SbH 3 , because, when passed into silver nitrate, it gives a black precipi- 
tate containing SbAg 3 . It would then be analogous to ammonia (NH 3 ), 
phosphine (PH 3 ), and arsenietted hydrogen (AsH 3 ). Very minute 
quantities of antimony are detected in chemical analysis by converting it 



CHLORIDES OF ANTIMONY. 841 

into this form. In sunshine, sulphur decomposes SbH 0> ; 2SbH., + S 6 
= Sb 2 S 3 + 3H 2 S. 

246. Chlorides of antimony. — Chlorine and antimony combine readily 
with evolution of heat and light; the chlorides are among the most im- 
portant compounds of this metal. 

Trichloride of antimony or antimonious chloride (SbCl 3 ) may be pre- 
pared by distilling three parts of powdered antimony with eight parts of 
corrosive sublimate, when calomel and an amalgam of antimony are left, 
and the trichloride of antimony (boiling at 433° I\) distils over — 

Sb 2 + 2HgCl 2 = SbCl 3 + SbHg + HgCl. 

It can also be obtained by boiling powdered antimony or sulphide of 
antimony to dryness with strong sulphuric acid, and distilling the anti- 
monious sulphate thus obtained with common salt. The trichloride is a 
soft crystalline fusible solid, whence its old name of butter of antimony. It 
may be dissolved in a small quantity of water, but a large quantity of water 
decomposes it, forming a bulky white precipitate, which is an oxy chloride 
of antimony (3SbCl 3 + 3H 2 = SbCl 3 .Sb 2 3 + 6HC1). When hot water is 
added to a hot solution of trichloride of antimony in hydrochloric acid, 
minute prismatic needles are deposited, containing 2SbCl 3 .5Sb 2 3 , and 
formerly called powder of Algaroth. The trichloride of antimony, in its 
behaviour with water, much resembles that of bismuth. Trichloride of 
antimony is occasionally used in surgery as a caustic; it also serves as a 
bronze for gun-barrels, upon which it deposits a film of antimony. 

Pentachloride of antimony or antimonic chloride (SbCl 5 ) is prepared b}~ 
heating coarsely powdered antimony in a retort, through which a stream 
of dry chlorine is passed (tig. 213), the neck of the retort being fitted into 
an adapter, which serves to condense the pentachloride. One ounce of 
antimony will require the chlorine from about 6 oz. of common manganese 
and 18 oz. (measured) of hydrochloric acid. The pure pentachloride is a 
colourless fuming liquid of a very suffocating odour; it combines energeti- 
cally with a small quantity of water, forming a crystalline hydrate, but 
an excess of water decomposes it into hydrochloric and antimonic acids, 
the latter forming a white precipitate; SbCl 5 + 3H 2 ■= HSb0 3 ■+ 5HC1. 
Pentachloride of antimony is employed by the chemist as a chlorinating 
agent; thus, olefiant gas (C 2 H 4 ) when passed through it, is converted into 
Dutch liquid (C 2 H 4 C1 2 ), and carbonic oxide into phosgene gas, the penta- 
chloride of antimony being converted into trichloride. 

The pentachloride of antimony is the analogue of pentachloride of phos- 
phorus, and a chlorosulphide of antimony (SbCl 3 S), corresponding to 
chlorosulphide of phosphorus, is obtained as a white crystalline solid by 
the action of hydrosulphuric acid upon pentachloride of antimony. 

247. Sid.phides of antimony. — Antimonious sulphide or sesqui 'sulphide of 
antimony (Sb 2 S 3 ) has been noticed as the chief ore of antimony. It is a 
heavy mineral (sp. gr. 4*63) of a dark grey colour and metallic lustre, 
occurring in masses which are made up of long prismatic needles. It fuses 
easily, and may be sublimed unchanged out of contact with air. It is 
easily recognised by heating it, in powder, with hydrochloric acid, when 
it evolves the odour of hydrosulphuric acid, and if the solution be poured 
into water, it deposits an orange precipitate (page 195). This orange 
sulphide, which has the same composition as the grey sulphide, is also 



342 SULPHIDES OF ANTIMONY — TIN. 

obtained by adding hydrosulphuric acid to a solution of a salt of antimony 
(for example, tartar emetic) acidulated with hydrochloric acid. It may 
be converted into the grey sulphide by the action of heat. The orange 
variety constitutes the antimony vermilion, the preparation of which has 
been described at page 214. Native sulphide of antimony is employed, 
in conjunction with potassium chlorate, in the friction-tube for firing 
cannon; it is also used in permission caps, together with potassium chlorate 
and mercuric fulminate. Its property of deflagrating with a bluish- white 
flame when heated with nitre, renders it useful in compositions for 
coloured fires. 

Glass of antimony is a transparent red mass obtained by roasting anti- 
monious sulphide in air, and fusing the product ; it contains about 8 parts 
of oxide and 1 part of sulphide of antimony. 

Red antimony ore is an oxysulphide of antimony, Sb 2 3 .2Sb 2 S 3 . 

Antimonic sulphide (Sb 2 S 5 ) is obtained as a bright orange-red precipitate 
by the action of hydrosulphuric acid upon a solution of pentachloride of 
antimony in hydrochloric acid. 

Both the sulphides of antimony are capable of combining with the 
alkaline sulphides to form sidpliantimonites and sulphantimoniates 
respectively. Hence they are easily dissolved by alkalies and alkaline 
sulphides. Even metallic antimony, in powder, is dissolved when gently 
heated with solution of potassium sulphide in which sulphur has been 
dissolved, any lead or iron which may be present being left in the residue, 
so that the antimony may be tested by this process as to its freedom from 
those metals. 

Mineral kermes is a variable mixture of sesquioxide and sesquisulphide 
of antimony, which is deposited as a reddish-brown powder from the solu- 
tion obtained by boiling sesquisulphide of antimony with potash or soda. 
It was formerly much valued for medicinal purposes. 

Schlippe's salt is the sodium sulphantimoniate (Na 3 SbS 4 .9H 2 0), and 
may be obtained in fine transparent tetrahedral crystals. This salt is 
sometimes used in photography. 

TIN. 

Sn = 118 parts by weight. 

248. Tin is by no means so widely diffused as most of the other metals 
which are largely used, and is scarcely ever found in the metallic state in 
nature. Its only important ore is that known as tin-stone, which is a 
binoxide of tin Sn0 2 , and is generally found in veins traversing quartz, 
granite, or slate. It is generally associated with arsenical iron pyrites, 
and with a mineral called loolfram, which is a tungstate of iron and 
manganese. 

Tin-stone is sometimes found in alluvial soils in the form of detached 
rounded masses ; it is then called stream tin ore, and is much purer than 
that found in veins, for it has undergone a natural process of oxidation 
and levigation exactly similar to the artificial treatment of the impure ore. 
These detached masses of stream tin ore are not unfrequently rectangular 
prisms with pyramidal terminations. 

The Cornish mines furnish the largest supplies of tin, and those of 
Malacca and Banca stand next. Tin-stone is also found in Bohemia, 
Saxony, and California. At the Cornish tin-works the purer portions 



EXTRACTION OF TIN. 



343 



of the ore are picked out by hand, and the residue, which contains 
quartz and other earthy impurities, together with copper pyrites and 
arsenical iron pyrites, is reduced to a coarse powder in the stamp- 
ing-mills, and washed in a stream of water. The tin-stone, being 
extremely hard, is not reduced to so fine a powder as the pyritous 
minerals associated with it, and these latter are therefore more readily 
carried away by the stream of water than the tin-stone. The removal 
of the foreign matters from the ore is also much favoured by the 
high specific gravity of the binoxide of tin, which is 6 "5, whilst that 
of sand or quartz is only 2*7, so that the latter would be carried off 
by a stream which would not disturb the former. So easily and com- 
pletely can this separation be effected, that a sand containing less 
than one per cent, of tin-stone is found capable of being economically 
treated. 

In order to expel any arsenic and sulphur which may still remain in 
the washed ore, it is roasted in quantities of 8 or 10 cwts. in a 
reverberatory furnace, when the sulphur is disengaged in the form of 
sulphurous acid gas, and the arsenic in that of arsenious oxide, the iron 
being left in the state of sesquioxide, and the copper partly as sulphate 
of copper, partly as unaltered sul- 
phide. To complete the oxidation 
of the insoluble sulphide of copper, 
and its conversion into the soluble 
sulphate, the roasted ore is moistened 
with water and exposed to the air 
for some days, after which the 
whole of the copper may be removed 
by again washing with water. 

A second washing in a stream of 
water also removes the sesquioxide 
of iron in a state of suspension, 
and this is much more easily 
effected than when the iron was in 
the form of pyrites, since the differ- 
ence between the specific gravity 
of this mineral (5*0) and that of 
the tin-stone (6*5) is far less than 
that between sesquioxide of iron 
and tin-stone. 

The ore thus purified contains 
between 60 and 70 per cent, of tin ; 
it is mixed very intimately with 
about i of powdered coal, and a little lime or fluor spar to form a fusible 
slag with the earthy impurities ; the mixture is sprinkled with water to 
prevent its dispersion by the draught of air, and thrown on the hearth 
(A, fig. 256) of a reverberatory furnace, in charges of between 20 and 
25 cwts. 

The temperature is not permitted to rise too high at first, lest a portion 
of the oxide of tin should Combine with the silica to form a silicate, from 
which the metal would be reduced with difficulty. 

During the first six or eight hours the doors of the furnace are kept shut, 
so as to exclude the air and favour the reducing action of the carbon 




Fiff. 256. 



344 • PUKIFICATION OF TIN. 

upon the binoxide of tin, the oxygen of which it converts into carbonic- 
oxide, leaving the tin in the metallic state to accumulate upon the hearth 
beneath the layer of slag. When the reduction is deemed complete, the 
mass is well stirred with an iron paddle to separate the metal from the 
slag ; the latter is run out first, and the tin is then drawn off into an iron 
pan (B), where it is allowed to remain at rest for the dross to rise to the 
surface, and is ladled out into ingot moulds. 

The slags drawn out of the smelting-furnace are carefully sorted, those 
which contain much oxide of tin being worked up with the next charge 
of ore, whilst those in which globules of metallic tin are disseminated are 
crushed, so that the metal may be separated by washing in a stream of 
water. 

The tin, when first extracted from the ore, is far from pure, being con- 
taminated with small quantities of iron, arsenic, copper, and tungsten. 
In order to purify it from these ; the ingots are piled into a hollow heap 
near the fire-bridge of a reverberatory furnace, and gradually heated to the 
fusing-point, when the greater portion of the tin flows into an outer basin, 
Avhilst the remainder is converted into the binoxide, which remains as 
dross upon the hearth, together with the oxides of iron, copper, and tung- 
sten, the arsenic having passed off in the form of arsenious oxide. Fresh 
ingots of tin are introduced at intervals, until about 5 tons of the metal 
have collected in the basin, which is commonly the case in about an hour 
after the commencement of the operation. 

The specific gravity of tin being very low (7*285), any dross which 
may still remain mingled with it does not separate very readily ; to 
obviate this, the molten metal is well agitated by stirring with wet 
wooden poles, or by lowering billets of wet wood into it, when the evolved 
bubbles of steam carry the impurities up to the surface in a kind of froth ; 
the stirring is continued for about three hours, and the metal is allowed to 
remain at rest for two hours, when it is skimmed and ladled into ingot 
moulds. It is found that, in consequence of the lightness of the metal, 
and its tendency to separate from the other metals with which it is con- 
taminated, the ingots which are cast from the metal first ladled out of the 
pot are purer than those from the bottom ; this is shown by striking the 
hot ingots with a hammer, when they break up into the irregular prismatic 
fragments known as dropped or grain-tin, the impure metal not exhibiting 
this extreme brittleness at a high temperature. The tin imported from 
Banca is celebrated for its purity (Straits tin). 

When the tin ore contains wolfram, it is usual to purify it, before smelt- 
ing, by fusion with sodium carbonate in a reverberatory furnace, when 
the tungstic acid is converted into sodium tungstate, which is dissolved out 
by water and crystallised. This salt finds an application in calico-printing. 

On the small scale, tin may be extracted from tin-stone by fusing 100 
grains with 20 grains of dried sodium carbonate, and 20 of dried borax, 
in a crucible lined with charcoal, exactly as in the extraction of iron (see 
page 321). 

The extraction is more easily effected by fusing 100 grains of tin- 
stone with 500 grains of potassium cyanide for fifteen minutes at a red heat. 

249. By its physical characters, tin is very readily distinguished from 
other metals. If a bar of tin be bent, it emits a peculiar crackling sound. 
With the exception of lead and zinc, it is the least tenacious of all the 



MANUFACTURE OF TIN-PLATE. 345 

metals in common use ; its ductility is therefore very low, and lead is the 
only common metal which it is more difficult to draw into wire at the 
ordinary temperature. Tin may, however, be drawn at 212° F. 

In fusibility, tin surpasses all the other common metals, becoming- 
liquid at 442° F., but it is not easily vaporised. Its malleability is also 
very great, only gold, silver, and copper exhibiting this quality in a higher 
degree. This malleability is shown in the manufacture of tin-foil, where 
plates of the best tin are hammered clown to a certain thinness, then cut 
up, laid upon each other, and again beaten till extended to the required 
degree. 

Tin-plate, it must be remembered, is made in a very different way, by 
coating sheets of iron with a layer of tin ; the best kind, known as block 
tin, being that which is covered with the thickest layer of tin, and after- 
wards hammered upon a polished anvil in order to consolidate the coating 
and make it adhere more firmly. Tin being unaltered by exposure to air 
at the ordinary temperature, will effectually protect the iron from rust as 
long as the coating of tin is perfect, but as soon as a portion of the tin is 
removed so as to leave the iron exposed, corrosion will take place very 
rapidly, because the two metals form a galvanic couple, which will decom- 
pose the water (charged with carbonic acid) deposited upon them from 
the air, and the iron, having the greater attraction for oxygen, will be the 
metal attacked. In the case of galvanised iron (coated with zinc), on the 
contrary, the zinc would be the metal attacked, and hence the greater 
durability of this material under certain conditions. 

For the manufacture of tin-plate, the very best iron refined with char- 
coal (see page 309) is employed, and the most important part of the process 
consists in cleansing the iron plates from every trace of oxide which would 
prevent the adhesion of the tiu. To effect this they are made to undergo 
several processes, of which the most important are — (1) immersion in 
diluted sulphuric acid ; (2) heating to redness ; (3) hammering and roll- 
ing to scale off the oxide ; (4) steeping in sour bran ; (5) immersion in 
mixed diluted sulphuric and hydrochloric acids ; (6) scouring with bran ; 
(7) washing with water; they are then dried for an hour in a vessel of 
melted tallow, which prevents contact of air, and immersed for an hour 
and a half in melted tin, the surface of which is protected from oxidation 
by tallow ; after draining, they are dipped a second time into the tin to 
thicken the layer ; then transferred to a bath of hot tallow to allow the 
superfluous tin to run down to the lower edge, whence it is afterwards 
removed by liquefying it in a vessel of melted tin, and shaking it off by 
a sharp blow. About 8 lbs. of tin are required to cover 225 plates, 
weighing 112 lbs. 

Terne-plate is iron coated with an alloy of tin and lead. 

In tinning the interior of copper vessels, in order to prevent the con- 
tamination of food with the copper, the surface is first thoroughly cleaned 
from oxide by heating it and rubbing over it a little sal-ammoniac, which 
decomposes any oxide of copper, converting it into the volatile chloride of 
copper (CuO + 2NH 4 Cl = CuCl 2 + H 2 + 2NH 3 ). A little resin is then 
sprinkled upon the metallic surface, to protect it from oxidation, and the 
melted tin is spread over it with tow. 

Pins (made of brass wire) are coated with tin by boiling them with 
cream of tartar (bitartrate of potash), common salt, alum, granulated tin, 
and water; the tin is oxidised at the expense of the water, and is then 



346 GUN METAL. 

ilissolved by the acid liquid, from which solution it is reduced by elec- 
trolytic action, for the tin is more highly electro-positive than the brass, 
and the latter acts as the negative plate. 

250. Alloys of tin. — The solder employed for tin wares is an alloy of 
tin and lead in various proportions, sometimes containing 2 parts of 
tin to 1 of lead (fine solder), sometimes equal weights of the two metals 
(common solder), and sometimes 2 parts of lead to 1 of tin (coarse solder). 
All these alloys melt at a lower temperature than tin, and therefore, than 
lead. In applying solder, it is essential that the surfaces to be united be 
quite free from oxide, which would prevent adhesion of the solder; 
this is insured by the application of sal-ammoniac, or of hydrochloric 
acid,* or sometimes of powdered borax, remarkable for its ready fusibility 
and its solvent power for the metallic oxides. 

Tin forms the chief part of the alloys known as pewter and Britannia 
metal, the former being composed of about 4 parts of tin and 1 of lead, 
whilst the latter contains, in addition to the tin, comparatively small 
quantities of antimony, copper, and lead. Another similar alloy is com- 
posed of 1 2 parts of tin, 1 of antimony, and a little copper. 

Gun metal is an alloy of 90*5 parts of copper with 9*5 of tin, especially 
valuable for its tenacity, hardness, and fusibility. In preparing this 
alloy, it is usual to melt the tin, in the first place, with twice its weight 
of copper, when a white, hard, and extremely brittle alloy {hard metal) is 
obtained. The remainder of the copper is fused in a deoxidising flame 
on the hearth of a reverberatory furnace, and the hard metal thoroughly 
mixed with it, long wooden stirrers being employed. A quantity of old 
gun metal is usually melted with the copper, and facilitates the mixing of 
the metals. When the metals are thoroughly mixed, the oxide is re- 
moved from the surface, and the gun metal is run into moulds made of 
loam, the stirring being continued during the running, in order to prevent 
the separation, to which this alloy is very liable., of a white alloy contain- 
ing a larger proportion of tin, which has a lower specific gravity, and 
would chiefly collect in the upper part of the casting (forming tin-spots). 
In casting cannon (erroneously called brass guns) the mould is placed 
perpendicularly, with the muzzle upwards, the upper part of the mould 
being about 3 feet longer than is required for the gun, so that a super- 
fluous cylinder of metal or dead-head is formed, in which the separated 
alloy collects, together with any oxide or dross which may have run out 
with the metal; this dead-head is cut off before the gun is turned and^ 
bored. The metal is run into the mould at a temperature as near its 
point of solidification as possible, so as to diminish the chance of separa- 
tion. The purest commercial qualities of copper and tin are always 
employed in gun metaL 

The brittle white alloy alluded to above as hard metal appears to be a 
chemical compound having the formula SnCu 4 (which requires 31*8 per 
cent, of tin, and 68*2 per cent, of copper), though the alloy which has the 
highest density, and which bears repeated fusion without alteration in its 
composition, corresponds to the formula SnCu 3 (38 "2 per cent, of tin). 
It is probably one of these alloys which forms the tin-spots or flaws in 
gun-metal castings. 

* It is customary to kill the hydrochloric acid by dissolving some zinc in it. The 
chloride of zinc is probably useful in protecting the work from oxidation. 



ALLOYS OF TIN. 347 

Bronze is essentially an alloy of copper and tin, containing more tin 
than gun metal; its composition is varied according to its application, 
small quantities of zinc and lead being often added to it. Bronze is 
affected by changes of temperature, in a manner precisely the reverse of 
that in which steel is influenced, for it becomes hard and brittle when 
allowed to cool slowly, but soft and malleable when quickly cooled. 
The art of making bronze was practised before any progress had been 
made in working iron, and ancient weapons were very commonly of this 
material. 

Bronze coin (substituted for the copper coinage) is composed of 95 
copper, 4 tin, and 1 zinc. 

Bell metal is an alloy of about 4 parts of copper and 1 of tin, to which 
lead and zinc are sometimes added. The metal of which musical instru- 
ments are made generally contains the same proportions of copper and 
tin as bell metal. At a little below a dark red heat, this alloy may be 
hammered into thin plates, by which Biche and Champion have succeeded 
in imitating the celebrated Chinese gongs. 

Speculum metal, employed for reflectors in optical instruments, con- 
sists of 2 parts of copper and 1 of tin, to which a little zinc, arsenic, and 
silver are sometimes added to harden it and render it susceptible of a 
high polish. 

A superior kind of type metal is composed of 1 part of tin, 1 of anti- 
mony, and 2 of lead. 

Tin is not dissolved by nitric acid, but is converted into a white 
powder, the binoxide of tin; hydrochloric acid dissolves it with the aid 
of heat, evolving hydrogen; but the best solvent for tin is a mixture of 
hydrochloric with a little nitric acid. When the metal is acted upon by 
hydrochloric acid, it assumes a crystalline appearance, which has been 
turned to account for ornamenting tin-plate. If a piece of common tin- 
plate be rubbed over with tow dipped in a warm mixture of hydrochloric 
and nitric acids, its surface is very prettily diversified (moire metallique) ; 
it is usual to cover the surface with a coloured transparent varnish. 

Commercial tin is liable to contain minute quantities of lead, iron, 
copper, arsenic, antimony, bismuth, gold, molybdenum, and tungsten. 
Pure tin may be precipitated in crystals by the feeble galvanic current 
excited by immersing a plate of tin in a strong solution of stannous 
chloride, covered with a layer of water, so that the metal may be in con- 
tact with both layers of liquid. 

251. Oxides of tin. — Two oxides of this metal are known — the prot- 
oxide, SnO, and the binoxide, SnQ 2 . 

Protoxide of tin (SnO), or stannous oxide, is a substance of little 
practical importance, obtained by decomposing stannous chloride with an 
alkali. Its colour varies, according to the mode of preparing it, from 
black or olive-coloured to red. It is a feebly basic oxide, and therefore 
dissolves in the acids ; it may also be dissolved by a strong solution of 
potash, but is then easily decomposed into metallic tin and the binoxide 
which combines with the potash. 

Binoxide of tin (Sn0 2 ), or stannic oxide, has been mentioned as the 
chief ore of tin, and is formed when tin is heated in air. Tin-stone, or 
cassiterite, as the natural form of this oxide is called, occurs in very hard 
square prisms, usually coloured brown by ferric oxide. In its insolubility 



348 CHLORIDES OF TIN. 

in acids it resembles crystallised silica, and, like that substance, it forms, 
when fused with alkalies or their carbonates, compounds which are soluble 
in water ; these compounds are termed stannates, the binoxide of tin being 
known as stannic anhydride. 

Sodium stannate is prepared, on the large scale, for use as a mordant 
by calico-printers. The prepared tin ore (page 343) is heated with solu- 
tion of sodium hydrate, and boiled down till the temperature rises to 500° 
or 600° F. ; or the tin ore is fused with sodium nitrate, when the nitric 
acid is expelled. It crystallises easily in hexagonal tables having the 
composition Na 2 Sn0 3 .4Aq., which dissolve easily in cold water, and are 
partly deposited again when the solution is heated. Most normal salts of 
the alkalies also cause a separation of sodium stannate from its aqueous 
solution. The solution of sodium stannate has, like the silicate, a strong 
alkaline reaction, and when neutralised by an acid, yields a precipitate of 
stannic acid, H 2 SnO B . If the solution of sodium stannate be added to an 
excess of hydrochloric acid, the stannic acid remains in solution, and if 
the liquid be dialysed (see page 114), a jelly is first formed, which 
gradually liquefies as the sodium chloride diffuses away, and eventually 
a pure aqueous solution of stannic acid is obtained, which is very easily 
gelatinised by the addition of a minute quantity of hydrochloric acid, or 
of some neutral salt. The great similarity between stannic and silicic 
acids is here very remarkable. When heated, stannic acid is converted 
into metastannic anhydride (Sn 5 O 10 ). 

Metastannic acid H 10 Sn 5 O 15 (dried at 100° C.) is obtained as a white crystalline 
hydrate (with 5Aq.) when tin is oxidised by nitric acid; when washed with water 
and dried by exposure to air, it has the above composition. When heated, it assumes 
a yellowish colour, and a hardness resembling that of powdered tin-stone. Putty 
powder, used for polishing, consists of metastannic anhydride ; as found in commerce 
it generally contains much oxide of lead. Metastannic acid is insoluble in water and 
diluted acids, and when fused with hydrated alkalies, is converted into a soluble 
stannate ; but if boiled with solution of potash it is dissolved in the form of potassium 
metastannate, which will not crystallise, like the stannate, but is obtained as a 
granular precipitate by dissolving potassium hydrate in its solution. This precipitate 
lias the composition K 2 O.Sn 5 O 10 .4Aq. ; it is very soluble in water, and is strongly 
alkaline. When it is heated to expel the water, it is decomposed, and the potash 
may be washed out with water, leaving metastannic acid. The hydrated metastannic 
acid maybe distinguished from stannic acid by the action of stannous chloride, which 
converts it into the yellow metastannate of tin (SnO.Sn 5 O 10 . 4Aq.). 

Stannate of tin is obtained as a yellowish hydrate by boiling stannous chloride with 
hydrated sesquioxide of iron; Fe 2 0. i + 2SnCl 2 = SnO.Sn0 2 + 2FeCl 2 . It is sometimes 
written Sn 2 3 , and called sesquioxide of tin. 

252. Chlorides of tin. — The two chlorides of tin correspond in com- 
position to the oxides. 

Stannous chloride or protocldoride of tin (SnCl 2 ) is much used by 
dyers and calico-printers, and is prepared by dissolving tin in hydrochloric 
acid, when it is deposited, on cooling, in lustrous prismatic needles 
(SnCl 2 .2Aq.), known as tin crystals or salts of tin. - The solution of the 
tin is generally effected in a copper vessel, in order to accelerate the 
action by forming a voltaic couple, of which the tin is the attacked metal. 
When gently heated, the crystals lose their water, and are partly de- 
composed, some hydrochloric acid being evolved (SnCl. 2 + H 2 = SnO 
+ 2HC1) ; but at a higher tempeiature, a great part of the chloride may 
be distilled in the anhydrous state ; the anhydrous chloride is generally 
prepared by distilling powdered tin with corrosive sublimate, when it 



SULPHIDES OF TIN. 349 

remains in the retort as a brilliant grey solid, which requires a bright red 
heat to convert it into vapour. When water is poured upon the crystals 
of stannous chloride, they are only partially dissolved, a white oxychloride 
of tin (SnCLjj.SnO.2Aq.) being separated. A moderately dilute solution 
of stannous chloride absorbs oxygen from the air, and deposits a white 
compound of stannic chloride and oxide; 2SnCl 2 + 2 = SnCl 4 .Sn0 9 . 
If the solution contains much free hydrochloric acid it remains clear, 
being entirely converted into stannic chloride. A strong solution of 
the chloride is not oxidised by the air, and the weak solution may be 
longer preserved in contact with metallic tin. Stannous chloride has a 
great attraction for chlorine as well as for oxygen, and is frequently 
employed as a deoxidising or dechlorinating agent. Tin may be preci- 
pitated from stannous chloride by the action of zinc, in the form of 
minute crystals. A very beautiful tin tree is obtained by dissolving 
granulated tin in strong hydrochloric acid, with the aid of heat, in the 
proportion of 8 measured oz. of acid to 1000 grs. of tin, diluting the solu- 
tion with four times its bulk of water, and introducing a piece of zinc. 

Stannic chloride, or bichloride, or tetrachloride of tin (SnCl 4 ), is ob- 
tained in solution when tin is heated with hydrochloric and nitric acids ; 
for the use of the dyer, the solution (nitromuriate of tin) is generally 
made with chloride of ammonium (sal-ammoniac) and nitric acid. The 
anhydrous perchloride is obtained by heating tin in a current of dry chlo- 
rine, when combination takes place with combustion, and the perchloride 
distils over as a heavy (sp. gr. 2 '2 8) colourless liquid, volatile (boiling- 
point, 240° L\), and giving suffocating white fumes in the air. When 
mixed with a little water, energetic combination takes place, and a 
crystalline hydrate (SnCl 4 .5Aq.) is formed, which is decomposed by an 
excess of water, with separation of hydrated stannnic acid. Stannic 
chloride forms crystallisable double salts with the alkaline chlorides. 
Pink scdt, used by dyers, is a compound of stannic chloride with chloride 
of ammonium, 2NH 4 Cl.SnCl 4 . 

253. Sulpirides of tin. — The protosidphide, or stannous sulphide (SnS), 
is found in Cornwall as tin pyrites, and may be easily prepared by heating- 
tin with sulphur, when it forms a grey crystalline mass. It is also ob- 
tained as a dark brown precipitate by the action of hydrosulphuric acid 
upon a solution of stannous chloride. Stannous sulphide is not dissolved 
by alkalies unless some sulphur be added, which converts it into stannic 
sulphide. 

Bisidphide of tin, or stannic sulphide (SnS 2 ), is commonly known as 
mosaic gold or bronze powder* and is used for decorative purposes. It is 
prepared by a curious process, which was devised in 1771, and must have 
been the result of a number of trials. 12 parts by weight of tin are dis- 
solved in 6 parts of mercury; the brittle amalgam thus obtained is 
powdered and mixed with 7 parts of sulphur and 6 of sal-ammoniac. 
The mixture is introduced into a Florence flask, which is gently heated 
in a sand-bath as long as any smell of hydrosulphuric acid is evolved ; 
the temperature is then raised to dull redness until no more fumes arc- 
disengaged. The mosaic gold is found in beautiful yellow scales at the 
bottom of the flask, and sulphide of mercury and calomel are deposited in 

* Bronze powder is also made by powdering finely laminated alloys of copper and zinc 
a little oil being used to prevent oxidation. 



350 TITANIUM. 

the neck. The mercury appears to be used for effecting the fine division 
of the tin, and the sal-ammoniac to keep down the temperature (by its 
volatilisation) below the point at which the bisulphide of tin is converted 
into protosulphide. 

Mosaic gold, like gold itself, is not dissolved by hydrochloric or nitric 
acid, but easily by aqua regia. Alkalies also dissolve it when heated. 
On adding hydrosulphuric acid to a solution of stannic chloride, the 
stannic sulphide is obtained as a yellow precipitate, which is sometimes 
formed only on boiling. 

254. Titanium (Ti = 50 parts. by weight), which stands in close chemical relation- 
ship to tin, used to be described as a very rare metal, but it has lately been found to 
exist in considerable quantity in iron" ores and clays, although no very important 
practical application has hitherto been found for it. The form in which it is gene- 
rally found is titanic acid (or anhydride) (Ti0 2 ), which occurs uncombined in the- 
minerals rutile, anatase, and brookite, the first of which is isomorphous with tin- 
stone, and is extremely hard like that mineral. In combination with oxide of 
iron, titanic acid is found in iron-sand, iserine, or menaccanitc (found originally 
at Menaccan in Cornwall), which resembles gunpowder in appearance, and is now 
imported in abundance from Nova Scotia and New Zealand. Some specimens of 
this mineral contain 40 per cent, of titanic acid, combined with protoxide of iron. 
To extract titanic acid from it, the finely-ground mineral is fused with three parts 
of carbonate of potash, when carbonic acid gas is expelled and titan ate of potash 
formed ; on washing the mass with hot water, this salt is decomposed, a part of its 
alkali being removed by the water, and an acid titanate of potash left, mixed with 
the oxide of iron. This is dissolved in hydrochloric acid, and the solution evapo- 
rated to dryness, when the titanic acid, and any silica which may be present, are 
converted into the insoluble modifications, and are left on digesting the residue 
again with dilute hydrochloric acid ; the residue is washed with water (by decanta- 
tion, for titanic acid easily passes through the filter), dried, and fused at a gentle 
heat with bisulphate of potash. The sulphuric acid forms a soluble compound with 
the titanic acid (Ti0 2 S0 3 ), which may be extracted by cold water, leaving the 
silica undissolved. The solution containing the titanic acid is mixed with about 
twenty times its volume of water, and boiled for some time, when the titanic acid 
is separated as a white precipitate, exhibiting a great disposition to cling as a film 
to the surface of the flask in which the solution is boiled, and giving it the appear- 
ance of being corroded. The titanic acid becomes yellow when strongly heated, and 
white again on cooling ; it does not dissolve in solution of potash like silica, but 
when fused with potash it forms a titanate, which is decomposed by water ; the 
acid titanate of potash which is left may be dissolved in hydrochloric acid, and 
if the solution be neutralised with carbonate of ammonia, hydrated titanic acid is 
precipitated, very much resembling alumina in appearance. By dissolving the 
gelatinous hydrate in cold hydrochloric acid, and dialysing, a solution of titanic acid 
in water is obtained, which is liable to gelatinise spontaneously if it contains more 
than 1 per cent, of the acid. 

Titanic acid is employed in the manufacture of artificial teeth, and for imparting 
a straw-yellow tint to the glaze of porcelain. 

If a mixture of titanic acicl and charcoal be heated to redness in a porcelain tube, 
through which dry chlorine is passed, tetrachloride of titanium (TiCl 4 ) is obtained 
as a colourless volatile liquid, very similar to perchloride of tin. By passing the 
vapour of the tetrachloride of titanium over heated sodium, the metallic titanium 
is obtained in prismatic crystals resembling specular iron ore in appearance. Like 
tin, it is said to dissolve in hydrochloric acid with liberation of hydrogen. The 
most remarkable chemical feature of titanium is its direct attraction for nitrogen, 
with which it combines when strongly heated in air. By passing ammonia gas 
over titanic acid heated to redness, a violet powder is formed, which is a nitride of 
titanium (TiN 2 ). Beautiful cubes of a copper colour and great hardness, formerly 
believed to beinetallic titanium, are found adhering to the slags of blast-furnaces 
in which titaniferous iron ores are smelted ; these contain about 77 per cent, of 
titanium, 18 of nitrogen, and rather less than 4 of carbon, and are believed to con- 
sist of a compound of cyanide with nitride of titanium, TiCy 2 .3Ti 3 N 2 . A similar 
compound is obtained by passing nitrogen over a mixture of titanic acid and charcoal 
heated to whiteness. 



TUNGSTEN. 351 

Violet-coloured crystals of trichloride of titanium (TiCl 3 ) are obtained by -passing- 
hydrogen charged with vapour of tetrachloride of titanium through a red hot porce- 
lain tube ; it forms a violet solution in water, which resembles stannous chloride in 
its reducing properties. 

When a solution of titanic acid (or acid titanate of potash) in hydrochloric acid is 
acted on by zinc, a violet solution is formed, which deposits, after a time, a blue (or 
green) precipitate, this appears to be a sesquioxide of titanium (Ti. 2 3 ), and rapidly 
absorbs oxygen from the air, being converted into titanic acid. A protoxide of 
titanium (TiO) is said to be obt lined as a black powder when titanic acid is strongly 
heated in a crucible lined with charcoal. 

Bisulphide of titanium is not precipitated, like bisulphide of tin, when hydro- 
sulphuric acid acts upon the tetrachloride ; but if a mixture of the vapour of' 
tetrachloride of titanium with hydrosulphurie acid is passed through a red hot tube,, 
greenish-yellow scales of the bisulphide, resembling mosaic gold, are deposited. 

Titanium, like tin, is classed among the tetratomic elements. 

255. Tungsten (W = 184) is chiefly found in the mineral wolfram, which occurs 
often associated with tin-stone, in large brown shining prismatic crystals, which 
are even heavier than tin-stone (sp. gr. 7 '3), from which circumstance the metal 
derives its name, tungsten, in Swedish, meaning heavy stone. The symbol (W) 
used for tungsten is derived from the Latin name wolframium. Wolfram contains 
the tungstates of iron and manganese in somewhat variable proportions, but its 
general composition is expressed by the formula 3FeW0 4 .MnW0 4 . Scheelite, tung- 
state of calcium (CaW0 4 ), is another mineral in which tungsten is found. A tungstate 
of copper has been found in Chili. 

Tungstate of sodium is employed by calico-printers as a mordant, and is sometimes 
applied to muslin, in order to render it uninflammable. It is obtained by fusing 
wolfram with carbonate of soda, an operation to which tin ores containing this 
mineral in large quantity are sometimes submitted previously to smelting them. 
Water extracts the sodium tungstate which may be crystallised in rhomboidal plates 
having the composition Na 2 W0 4 .2Aq. When a solution of this salt is mixed with 
an excess of hydrochloric acid, white hydrated tungstic acid (H 2 W0 4 .Aq.) is pre- 
.cipitated, while hot solutions give a yellow precipitate of H 2 W0 4 ; but if dilute 
hydrochloric acid be carefully added to a 5 per cent, solution of sodium tungstate 
in sufficient proportion to neutralise the alkali, and the solution be then dialysed 
(page 114), the sodium chloride passes through, and a pure aqueous solution of 
tungstic acid is left in the dialyser. This solution is unchanged by boiling, and 
when evaporated to dryness, it forms vitreous scales, like gelatine, which adhere verv 
strongly to the dish. It redissolves in one-fourth of its weight of water, forming a 
solution of the very high specific gravity 3 2, which is, therefore, able to float glass. 
The solution has a bitter and astringent taste, and decomposes sodium carbonate 
with effervescence. It becomes green when exposed to air, from the deoxidising 
action of organic dust. When tungstic acid is heated, it loses water, and becomes 
of a straw-yellow colour, and insoluble in acids. There are at least two modifica- 
tions of tungstic acid, which bear to each other a relation similar to that between 
stannic and metastannic acids. 

Barium tungstate has been employed as a substitute for white lead in painting. 

The most characteristic property of tungstic acid is that of yielding a blue oxide 
(W0 2 .W0 3 ), when placed in contact with hydrochloric acid and metallic zinc. 

A very remarkable compound containing tungstic acid and soda is obtained when 
bitungstate of soda (Na 2 0.2W0 3 4H 2 0) is fused with tin. If the fused mass be 
treated with strong potash, to remove free tungstic acid, washed with water, and 
treated with hydrochloric acid, yellow lustrous cubical crystals are obtained, which 
are remarkable, among sodium compounds, for their resistance to the action of water, 
of alkalies, and of all acids except hydrofluoric. The composition of these crystals. 
appears to be Na. 2 O.W0 2 .2W0 3 . 

The tungstoborates are remarkable salts containing W0 3 and B 2 3 combined with 
metallic oxides. Their solutions have a very high specific gravity ; that of cadmium 
tungstoborate has the sp. gr. 3 '6, and is used to effect the mechanical separation of 
minerals of different specific gravities. Thus, a diamond (sp. gr. 3 - 5) would float ; 
whilst a white sapphire (sp. gr. 4*0) would sink in the solution. 

The binoxide of tungsten (W0 2 ) appears to be an indifferent oxide, and is obtained 
by reducing tungstic acid with hydrogen at a low red heat, when it forms a brown 
powder which is dissolved by boiling in solution of potash, hydrogen being evolved, 
and potassium tungstate formed. 



352 NIOBIUM — COPPER. 

Metallic tungsten is obtained by reducing tungstic acid with charcoal at a white 
heat, as an iron-grey infusible metal of sp. gr. 17*6, very hard, not affected by 
hydrochloric or diluted sulphuric acid, but converted into tungstic acid by the action 
of nitric acid. "When tungsten is dissolved in about ten times its weight of fused 
steel, it forms an extremely hard alloy. 

When tungsten is heated in chlorine, the tungstic chloride (WC1 6 ) sublimes in 
bronze coloured needles which are decomposed by water. When gently heated in 
hydrogen, it is converted into the tetrachloride (WC1 4 ), but if its vapour be mixed 
with hydrogen and passed through a glass tube heated to redness, metallic tungsten 
is obtained in a form in which it is not dissolved, even by aqua regia, though it may 
be converted into potassium tungstate by potassium hypochlorite mixed with potash 
in excess. 

Bisulphide of tungsten (WS 2 ) is a black crystalline substance resembling plumbago, 
obtained by heating a mixture of bitungstate of potash with sulphur, and washing 
with hot water. Trisulphide of tungsten ( WS 3 ) is a sulphur-acid, obtainable as a 
brown^precipitate by dissolving tungstic acid in an alkaline sulphide, and precipitat- 
ing by an acid. 

256. Niobium (Nb = 94) (formerly called columbium) has been obtained from a 
rare dark grey hard crystalline mineral known as columbite, occurring in Massa- 
chusetts. This mineral contains niobic oxide (Nb0 2 ) combined with the oxides of 
iron and manganese. 

The niobic oxide is extracted by a laborious process, and forms a white powder, 
sparingly soluble in hydrochloric acid. Niobium itself has been obtained as a 
black powder insoluble in nitric acid and in aqua regia, but dissolved by a mixture 
of nitric and hydrofluoric acids. 

Tantalum, formerly believed to be identical with niobium, occurs in the tantalite 
and yttrotantalitc of Sweden, which contain tantalic oxide (Ta0 2 ) resembling niobic 
oxide. 

Niobium and tantalum have recently been found to the amount of 2 or 3 per cent, 
in the tin ore of Montebras. 

COPPER 

Cu" = 63 "5 parts by weight. 

257. Metallic copper is met with in nature more abundantly than 
metallic iron, though the compounds of the latter metal are of more fre- 
quent occurrence than those of the former.* A very important vein of 
metallic copper, of excellent quality, occurs near Lake Superior in North 
America, from which 6000 tons were extracted in 1858. Metallic copper 
is also sometimes found in Cornwall, and copper sand, containing metallic 
copper and quartz, is imported from Chili. 

Ores of copper. — The most important English ore of copper is copper 
pyrites, which is a double sulphide, containing copper, iron, and sulphur 
in the proportions indicated by the formula CuFeS 2 . It may be known 
by its beautiful brass yellow colour and metallic lustre. Copper pyrites 
is found in Cornwall and Devonshire, and is generally associated with 
arsenical pyrites (FeS 2 .FeAs 2 ), tin-stone (Sn0 2 ), quartz, fluor spar, and clay. 
A very attractive variety of copper pyrites is called cariegated copper ore 
or peacock copper, in allusion to its rainbow colours ; its simplest for- 
mula is Cu 3 FeS 3 . This variety is found in Cornwall and Killamey. 

Coppjer glance (Cu S) is another Cornish ore of copper, of a dark grey 
colour and feeble metallic lustre. 

Grey copper ore, also abundant in Cornwall, is essentially a compound 
of the sulphides of copper and iron with those of antimony and arsenic, 
but it often contains silver, lead, zinc, and sometimes mercury. 

■• Copper is not at all frequently found in animals or vegetables ; out Church has made 
the remarkable observation that the red colouring matter (turacine) of the feathers of the 
plantain-eater (tourocn) contains as much as 5 - 9 per cent, of copper. 



COPPER OEES. 



353 



Malachite, a basic carbonate of copper, is imported from Australia 
(Burra Burra), and is also found abundantly in Siberia. Green malachite, 
the most beautifully veined ornamental variety, has the composition 
CuC0 3 ,Cu(OH) 2 , and blue malachite is 2CuC0 3 .Cu(OH) 2 . 

Red copper ore (Cu 2 0) is found in West Cornwall, and the black oxide 
(CuO) is abundant in the north of Chili. 

258. The seat of English copper-smelting is at, Swansea, which is 
situated in convenient proximity to the anthracite, coal employed in the 
furnaces. The chemical process by which copper is extracted from the 
ore includes three distinct operations — (1) the roasting, to expel the 
arsenic and part of the sulphur, and to convert the sulphide of iron into 
oxide of iron ; (2) the fusing with silica, to remove the oxide of iron as 
silicate, and to obtain the copper in combination with sulphur only ; and 
(3) the roasting of this combination of copper with sulphur, in order to 
expel the latter and obtain metallic copper. 

The details of the smelting process appear somewhat complicated, 
because it is divided into several stages to allow of the introduction of the 
different varieties of ore to be treated. Thus, the first roasting process is 
unnecessary for the oxides and carbonates of copper, and the fusion with 
silica is not needed for those ores which are free from iron, so that they 
may be introduced at a later stage in the operations. 

(1) Calcining or roasting the ore to expel arsenic and part of the 
sulphur. — The ores having been sorted, and broken into small pieces, are 




Fig. 257. 

mixed so as to contain from 8 to 10 per cent, of copper, and roasted, in 
quantities of about three tons, for at least twelve hours, on the spacious 
hearth (H, fig. 258) of a reverberatory 
furnace (fig. 257), at a temperature 
insufficient for fusion, being occasionally 
stirred to expose them freely to the 
action of the air, which is admitted into 
the furnace through an opening (0) in 
the side of the hearth upou which the 
ore is spread. The oxygen of the air 
converts a part of the sulphur into S0 9 , 
and the bulk of the As into As.,0 3 , 

which passes off in the form of vapour. -p io . 2 58 

A part of the sulphide of iron is converted 

into ferrous sulphate (FeS0 4 ) by absorbing oxygen at an early stage of 
the process, and this sulphate is afterwards decomposed at a higher 

Z 




354 



WELSH COPPER-SMELTING PROCESS. 



temperature, evolving S0 2 and S0 3 , and leaving oxide of iron. A portion 
of the sulphide of copper is also converted into oxide of copper during 
the roasting, so that the roasted ore consists essentially of a mixture of 
oxide and sulphide of copper with oxide and sulphide of iron. Since the 
sulphide of iron is more easily oxidised than sulphide of copper, the 
greater part of the latter remains unaltered in the roasted ore. 

During the roasting of copper ore dense white fumes escape from the 
furnaces. This copper smoke, as it is termed, contains As 2 3 , S0 2 , S0 3 , 
and HF, the latter being derived from the fluor spar associated with the 
ore ; if allowed to escape, these fumes seriously contaminate the air in 
the neighbourhood, and copper-smelters are endeavouring to apply some 
method of condensing, and perhaps turning them to profitable account. 

(2) Fusion for coarse metal to remove the oxide of iron by dissolving it 
with silica at a high temperature. — The roasted ore is now mixed with 

metal slag from process 4, and 
with ores containing silica and 
oxides of copper, but no sul- 
phur; the mixture is introduced 
into the ore furnace (fig. 259), 
and fused for five hours at a 
higher temperature than that 
employed in the previous opera- 
tion. In this process fluor spar 
is sometimes added in order to 
increase the fluidity of the slag. 
The oxide of copper acts upon 
the sulphide of iron still con- 
tained in the roasted ore, with 
formation of sulphide of copper 
and oxide of iron, but since 
there is more sulphide of iron 
present than the oxide of copper 
can decompose, the excess of 
sulphide of iron combines with 
the sulphide of copper to form 
a fusible compound, which 
separates from the slag," and collects in the form of a matt or regiclusoi 
coarse metal, in a cavity (C) on the hearth of the furnace : it is run out 
into a tank of water (T) in order to granulate it, so that it may be better 
fitted to undergo the next operation. 

The oxide of iron combines with the silica contained in the charge, to 
form a fusible ferrous silicate (ore-furnace slag), which is raked out into 
moulds of sand, and cast into blocks used for rough building purposes in 
the neighbourhood. 

The composition of the coarse metal corresponds pretty closely with the 
formula CuFeS 2 . It contains from 33 to 35 per cent, of copper ; whilst 
the original ore, before roasting, is usually sorted so that it may contain 
about 8*5 per cent. 

The ore-furnace slag is approximately represented by the formula 
FeO.Si0 2 ; but it contains a minute proportion of copper, as is shown by 
the green efflorescence on the walls in which it is used around Swansea. 
Fragments of quartz are seen disseminated through this slag. 




Fig. 259. 



COPPER- SMELTING PROCESS. 3 00 

(3) Calcination of the coarse metal to convert the greater part of the 
sulphide of iron into oxide. — The granulated coarse metal is roasted at a 
modera te heat for twenty-four hours, as in the first operation, so that the 
oxygen of the air may decompose the sulphide of iron, removing the 
sulphur as sulphurous acid gas, and leaving the iron in the form of 
oxide. 

(4) Fusion for white metal to remove the whole of the iron as silicate. — 
The roasted coarse metal is mixed with roaster and refinery slags from 
processes 5 and 6, and with ores containing carbonates and oxides of 
copper, and fused for six hours, as in the second operation. Any sulphide 
of iron which was left unchanged in the roasting is now converted into 
oxide of iron by the oxide of copper, the latter metal taking the sulphur. 
The whole of the oxide of iron combines with the silica to form a fusible 
slacr, the composition of which is approximately represented by the for- 
mula 3Fe0.2Si0 2 . 

The matt or regulus of white metal, which collects beneath the slag, 
is nearly pure cuprous sulphide (Cu 2 S), half the sulphur existing 
in the cupric sulphide (CuS) having been removed by oxidation in the 
furnace. The white metal is run into sand-moulds and cast into ingots. 
The tin and other foreign metals usually collect in the lower part of the 
ingot, so that, for making best selected copper, the upper part is broken off 
and worked separately, the inferior copper obtained from the lower part of 
the ingot being termed tile-copper. The ingots of white metal often con- 
tain beautiful tufts of metallic copper in the form of copper moss. 

The slag separated from the white metal (metal slag) is much more fluid 
than the ore-furnace slag, and contains so much silicate of copper that it 
is preserved for use in the melting for coarse metal. 

(5) Boasting the white metal to remove the sidphur and obtain blistered 
copper. — The ingots of white metal (to the amount of about 3 tons) are 
placed upon the hearth of a reverberatory furnace, and heated for four 
hours to a tempearture just below fusion, so that they may be oxidised at 
the surface, the sulphur passing off as sulphurous acid gas, and the copper 
being converted into oxide. During this roasting the greater part of the 
arsenic, generally present in the fine metal, is expelled as As 2 3 . The 
temperature is then raised, so that the charge may be completely fused, 
after which it is lowered again till the twelfth hour. The oxide of copper 
now acts upon the sulphide of copper to form metallic copper and sul- 
phurous acid gas, which escapes, with violent ebullition, from the melted 
mass ; Cu 2 S -I- 2CuO = S0 2 + Cu 4 . When this ebullition ceases, the tem- 
perature is again raised so as to cause the complete separation of the copper 
from the slag, and the metal is run out into moulds of sand. Its name 
of blister copper is derived from the appearance caused by the escape of 
the last portions of S0 2 from the metal when solidifying in the mould. 

The slag (roaster slag) is formed in this operation by the combination 
of a part of the oxide of copper with silica derived from the sand 
adhering to the ingots, and from the hearth of the furnace. The slag 
also contains the silicates of iron and of other metals, such as tin and lead, 
which might have been contained in the white metal. This slag is used 
again in the melting for white metal. 

(6) Refining to remove foreign metals. — This process consists in slowly 
fusing 7 or 8 tons of the blistered copper in a reverberatory furnace, so 



356 



POLING OF COPPER: 



that the air passing through the furnace may remove any remaining sul- 
phur as sulphurous acid gas, and may oxidise the small quantities of iron, 
tin, lead, &c, present in the metal. Of course, a large proportion of the 
copper is oxidised at the same time, and the cuprous oxide, together 
with the oxides of the foreign metals, combine with silica (from the hearth 
or from adhering sand) to form a slag which collects upon the surface of 
the melted copper. A portion of the cuprous oxide is dissolved by the 
metallic copper, rendering it brittle or dry copper. 

(7) Toughening or poling, to remove a part of the oxygen and bring the 
copper to tough-pitch.- — After about twenty hours the slag is skimmed 
from the metal, a quantity of anthracite is thrown over the surface to pre- 
vent further oxidation, and the metal is poled, i.e., stirred with a pole of 
young wood, until a small sample, removed for examination, presents a 
peculiar silky fracture, indicating it to be at tough-pitch, when it is cast 
into ingots. 

The chemical change during the poling appears to consist in the re- 
moval of the oxygen contained in the cuprous oxide present in the metal, 
by the reducing action of the combustible gases disengaged from the wood. 
The presence of a small proportion of cuprous oxide is said to confer 
greater toughness upon the metal, so that if the poling be continued until' 
the whole of the oxygen is removed, overpoled copper of lower tenacity is 
obtained. On the other hand, the brittleness of underpoled coppjer is due 
to the presence of cuprous oxide in too large proportion. Tough-cake 
copper is that which has been poled to the proper extent. 

When the copper is intended for rolling, a small quantity (not exceed- 
ing J per cent.) of lead is generally added to it before it is ladled into the 
ingot moulds. Apparently the oxide of lead formed by the action of the 
air assists in removing some of the impurities in the form of slag (scori- 
fication). 

The chemical changes which take place during the above processes will 
be more clearly understood after inspecting the subjoined table, which 
exhibits the composition of the products obtained at different stages of the 
process, these being distinguished by the same numerals as were employed- 
in the above description. 



Products obtained in smelting Ores of Copper. 



In 100 parts. 


Ore. 


Roasted 
Ore. 


Coarse 
Metal. 


Roasted 
Coarse 
Metal. 


White 
Metal. 


Blister 
Copper. 


Refined 
Copper. 


Tough r 
pitch) 
Copper. 


Copper, 
Iron, 
Sulphur, 
Oxygen, . 
Silica, . . 


8-2 
17-9 
19-9 

1-0 
34-3 


(1) 
8-6 
17-6 
12-5 
4-5 
34-3 


(2) 
337 
33-6 
29-2 


(3) 
337 
33-6 
13-0 
11-0 


(4) 
77'4 

7 
21-0 


(5) 

98-0 

0-5 

0-2 


(6) 
99-4 
trace 
trace 

0-4 


(7) 
99-6 
trace 
trace 
0-03 


Slags. 


Ore 
Furnace 




Metal. 


Roaster. 


Refinery 




Oxide of iron (FeO), 

Suboxide of copper (Cu 2 0), 

Silica, ...... 


(2) 
54-0 

0-5 
45-0 




(4) 
56-0 

0-9 
33-8 


(5) 
28-0 
16-9 
47-5 


(6) 

3-1 

39-2 

47-4 





EXTRACTION OF COPPER IN THE LABORATORY. 357 

Blue metal is the term applied to trie regulus of white metal (from process 4) 
■when it still contains a considerable proportion of sulphide of iron, in consequence 
of a deficient suppty of oxide of copper in the furnace. Pimple metal is obtained in 
the same operation when the oxide of copper is in excess, so that a portion of the 
copper is reduced, as in process 5, with evolution, of sulphurous acid gas, which pro- 
duces the pimply appearance in escaping. The reduced copper gives a reddish colour 
to the pimple copper. Coarse copper is a similar intermediate stage between white 
metal and blistered copper. Tile copper is that extracted from the bottoms of the 
ingots of white metal, when the tops have been detached for making best select 
copper. Rosette or rose copper is obtained by running water upon the toughened 
metal, so as to enable the metal to be removed in films. Anglesea or Mona copper is 
a very tough copper, reduced by metallic iron from the blue icater of the copper 
mines, which contains sulphate of copper. 

A new method (Hollway 's process) has recently been proposed for the treatment of 
cupreous pyrites, which consists in blowing air through it in a melted state in a 
Bessemer's converter (p. 313), when the combustion of the sulphur maintains a very 
high temperature, and the bulk of the copper sinks to the bottom as a regulus, con- 
taining comparatively small quantities of iron and sulphur, whilst the iron is converted 
into oxide, which forms a slag with silica, added for that purpose. The copper 
regulus contains all the silver and gold present in the pyrites. It is proposed to 
utilise the S0 2 resulting from the combustion of the sulphur, by converting it into 
H 2 S0 4 . 

259. For the purpose of illustration, copper may be extracted from copper pyrites 
on the small scale in the following manner : — 

200 grains of the powdered ore are mixed with an equal weight of dried borax, 
and fused in a covered earthen crucible (of about 8 oz. capacity), at a full red heat 
for about half an hour. The earthy matters associated with the ore are dissolved 
by the borax, and the pure copper pyrites collects at the bottom of the crucible. The 
contents of the latter are poured, into 
an iron mould (scorifying mould, fig. 
260), and when the mass has set, it 
is dipped into water. The semi- 
metallic button is then easily detached 
from the slag by a gentle blow ; it is 
weighed, finely powdered in an iron 
mortar, and introduced into an 
earthen crucible, which is placed 
obliquely over a dull fire, so that it 
may not become hot enough to fuse ■^ 1 S- 260. 

the ore, which should be stirred 

occasionally with an iron rod to promote the oxidation of the sulphur by the air. 
When the odour of S0 2 is no longer perceptible, the crucible is placed in a Sefstrom's 
blast-furnace (fig. 251), and exposed for a few minutes to a bright red heat, in 
order to decompose the sulphates of iron and copper. "When no more white fumes 
of S0 3 are perceived, the crucible is lifted from the fire, held over the iron mortar, 
and the roasted ore quickly scraped out of it with a steel spatula. This mixture of 
the oxides of copper and iron is reduced to a fine powder, mixed with 600 grains 
of dried carbonate of soda and 60 grains of powdered charcoal, returned to the 
same crucible, covered with 200 grains of dried borax, and heated in a Sefstrom's 
furnace for twenty minutes. The crucible is then allowed to cool partly, plunged 
into water to render it brittle, and carefully broken to extract the button of metallic 
copper, which is weighed to ascertain the amount contained in the original ore. 

260. Effect of impurities upon the quality of copper. — The information 
possessed by chemists upon this subject is still very limited. It has been 
already mentioned that the presence of a small proportion of cuprous 
oxide in commercial copper is found to increase its toughness. It is 
believed that copper, perfectly free from metallic impurities, is not im- 
proved in quality by the presence of the oxide, but that this substance 
has the effect of counteracting the red-shortness (see page 314) of com- 
mercial copper, caused by the presence of foreign metals. 

Sulphur, even in minute proportion, appears seriously to injure the 
malleability of copper. 




358 PROPERTIES OF COPPER. 

Arsenic is almost invariably present in copper, very frequently amount- 
ing to 0*1 per cent., and does not appear to exercise any injurious influence 
in this proportion ; indeed, its presence is sometimes stated to increase 
the malleability and tenacity of the metal. 

Phosphorus is not usually found in the copper of commerce. When 
purposely added in quantity varying from 0*12 to 0*5 per cent, it is found 
to increase the hardness and tenacity of the copper, though rendering it 
somewhat red-short. Phosphor-bronze is a very hard compound of this 
description. 

Tin, in minute proportion, is also said to increase the toughness of 
copper, though any considerable proportion renders it brittle. 

Antimony is a very objectionable impurity, and is by no means uncom- 
mon in samples of copper. 

Nickel is believed to injure the quality of copper in which it occurs. 

Bismuth and silver are very generally found in marketable copper, but 
their effect upon its quality has not been clearly determined. 

All impurities appear to affect the malleability and tenacity of copper 
more perceptibly at high than at low temperatures. 

The conducting power of copper for electricity is affected in an extra- 
ordinary degree by the presence of impurities. Thus, if the conducting 
power of chemically pure copper be represented by 100, that of the very 
pure native copper from Lake Superior has been found to be 93, that of 
the copper extracted from the malachite of the Burra Burra mines in 
South Australia was 89, whilst that of Spanish copper, remarkable for 
containing much arsenic, was only 14. 

Pure copper is obtained by decomposing a solution of pure sulphate of 
copper by the galvanic current, as in the electrotype process. If the 
negative wire be attached to a copper plate immersed in the solution, the 
pure copper may be stripped off this plate in a sheet. 

261. Properties of copper. — The most prominent character which 
confers upon copper so high a rank among the useful metals is its mal- 
leability, which allows it to be readily fashioned under the hammer, and 
to be beaten or rolled out into thin sheets ; among the metals in ordinary- 
use, only gold and silver exceed copper in malleability, and the com- 
parative scarcity of those metals leads to the application of copper for 
most purposes where great malleability is requisite. 

Although, in tenacity or strength, copper ranks next to iron, it is still 
very far inferior to it, for a copper wire of ~$ inch in diameter will support 
only 385 lbs., while a similar iron wire will carry 705 lbs. without 
breaking ; and in consequence of its inferior tenacity, copper is less ductile 
than iron, and does not admit of being so readily drawn into exceedingly 
thin wires. 

The comparative ease with which copper may be fused, allows it to be 
cast much more readily than iron ; for it will be remembered that the 
latter metal can be liquefied only by the highest attainable furnace heat, 
whereas copper can be fused at about 1300° C. (2372° F.), a temperature 
generally spoken of as a bright red heat. 

As being the most sonorous of metals, copper has been, from time 
immemorial, employed in the construction of bells and musical instru 
ments. The readiness with which it transmits electricity is turned to 
account in telegraphic communication, its conducting power being almost 



EFFECT OF SEA WATER UPON COPPER. 359 

equal to that of silver, which is the best of electric conductors. In 
conducting power for heat, copper is surpassed only by silver and gold. 

Copper is not so hard as iron, and is somewhat heavier, the specific 
gravity of cast copper being 8 '92, and that of hammered or drawn 
copper 8*95. 

The resistance of copper to the chemical action of moist air gives it a 
great advantage over iron for many uses, and the circumstance that it does 
not decompose water in presence of acids enables it to be employed as 
the negative plate in galvanic couples. 

262. Effect of sea icater upon copper.- — When copper is placed in a 
solution of salt in water, no perceptible action takes place ; but in the 
course of time, if the air be allowed access, it becomes covered with a 
green coating of oxychloride of copper (CuCl 2 .3Cu0.4H 2 0), the action 
probably consisting, first, in the conversion of the copper into oxide by 
the air, and afterwards in the decomposition of the oxide by the sodium 
chloride ; 4CuO + 2NaCl + H 2 = CuCl 2 . 3CuO + 2XaHO. The surface 
of the copper is thus corroded, and in the case of a copper-bottomed 
ship, the action of sea water not only occasions a great waste of copper, 
but roughens the surface of the sheathing, and affords points of attach- 
ment to barnacles, &c, which injure the speed of the vessel. Many, 
attempts have been made to obviate this inconvenience. Zinc has been 
fastened here and there to the outside of the copper, placing the latter 
in an electro-negative condition; the copper has been coated with various 
compositions, but with very indifferent success. Muntz metal or yellow 
sheathing, or malleable brass, an alloy of 3 parts of copper and 2 parts 
of zinc, has been employed with some advantage in place of copper, for 
it is very much cheaper and somewhat less .easily corroded ; but the 
difficulty is by no means overcome. Copper containing about 0*5 per 
cent, of phosphorus is said to be corroded by sea water much less easily 
than pure copper. 

263. Danger attending the use of copper vessels in cooking food. — The 
use of copper for culinary vessels has occasionally led to serious conse- 
quences, from the poisonous nature of its compounds, and from ignorance 
of the conditions under which these compounds are formed. A perfectly 
clean surface of metallic copper is not affected by any of the substances 
employed in the preparation of food, but if the metal has been allowed to 
remain exposed to the action of the air, it becomes covered with a film of 
oxide of copper, and this subsequently combines with water and carbonic 
acid gas derived from the air to produce a basic carbonate of copper,* 
which, becoming dissolved, or mixed with the food prepared in these 
vessels, confers upon it a poisonous character. This danger may be 
avoided by the use of vessels which are perfectly clean and bright, but 
even from these, certain articles of food may become contaminated with 
copper, for this metal is much more likely to be oxidised by the air when 
in contact with acids (vinegar, juices of fruits, &c), or with fatty matters, 
or even with common salt ; and if oxide of copper be once formed, it will 
be readily dissolved by such substances. Hence it is usual to coat the 
interior of copper vessels with tin, which is able to resist the action of 
the air, even in the presence of acids and saline matters. 

* Often erroneously called verdigris, which is really a basic acetate of copper. 



360 ALLOYS OF COPPEK. 

264. Useful alloys of copper with other metals. — The most important 
alloys of which, copper is a predominant constituent are the following : — 

Brass — 64 copper, 36 zinc. 

Muntz metal — 60 to 64 copper, 40 to 36 zinc. 

German silver — 51 copper, 30*5 zinc, 18*5 nickel. 

Aich or Gedge's metal — 60 copper, 38*2 zinc, 1*8 iron. 

Sterro-metal — 55 copper, 42*4 zinc, 0*8 tin, 1*8 iron. 

Bell metal— 78 copper, 22 tin. 

Speculum metal — 66*6 copper, 33*4 tin. 

Bronze — 80 copper, 4 tin, 16 zinc. 

Gun metal — 90 - 5 copper, 9 '5 tin. 

Bronze coinage — 95 copper, 1 zinc, 4 tin. 

Aluminium bronze — 90 copper, 10 aluminium. 
Brass is made by melting copper in a crucible, and adding rather more 
than half its weight of zinc. It is difficult to decide whether brass is a 
true chemical compound or a mere mechanical mixture of copper and 
zinc, because it is capable of dissolving either of those metals when in a 
state of fusion. The circumstance that it can be deposited by decom- 
posing a solution containing copper and zinc by the galvanic current, 
would appear to indicate that it is a chemical compound, and its physical 
properties are not such as would be expected from a mere mixture of its 
constituents. A small quantity of tin is added to brass intended for 
door-plates, which renders the engraving much easier. When it has to 
be^turned or filed, about 2 per cent, of lead is usually added to it, in 
order to prevent it from adhering to the tools employed. Brass cannot 
be melted without losing a portion of its zinc in the form of vapour. 
When exposed to frequent vibration (as in the suspending chains of chan- 
deliers) it suffers an alteration in structure and becomes extremely brittle. 
The solder used by braziers consists of equal weights of copper and zinc. 
In order to prevent ornamental brass-work from being tarnished by the 
action of air, it is either lacquered or bronzed. Lacquering consists 
simply in varnishing the brass with a solution of shellac in spirit, 
coloured with dragon's blood. Bronzing is effected by applying a solution 
of arsenic or mercury, or platinum, to the surface of the brass. By the 
action of arsenious oxide dissolved in hydrochloric acid, upon brass, the 
latter acquires a coating composed of arsenic and copper, which imparts a 
bronzed appearance, the zinc being dissolved in place of the arsenic, which 
combines with the copper at the surface. A mixture of corrosive sub- 
limate (mercuric chloride HgCl 2 ) and acetic acid is also sometimes 
employed, when the mercury is displaced by the zinc, and - precipitated 
upon the surface of the brass, with which it forms a -bronze -like amalgam. 
For bronzing brass instruments, such as theodolites, levels, &c, a solu- 
tion of chloride of platinum is employed, the zinc of the brass precipi- 
tating a very durable film of metallic platinum upon its surface (PtCl 4 
+ Zn 2 = Pt + 2ZnCl 2 ). Aich metal is a kind of brass containing iron, 
and has been employed for cannon, on account of its great strength. At 
a red heat it is very malleable. 

Sterro metal (o-reppos, strong) is another variet} r of brass containing iron 
and tin, said to have been discovered accidently in making brass with 
the alloy of zinc and iron obtained during the process of making gal- 
vanised iron (page 284). It possesses great strength and elasticity, and 
is used by engineers for the. pumps of hydraulic presses. 



OXIDES OF COPPER. 361 

Aluminium bronze has been already noticed, and the alloys of copper 
and tin have been described under the latter metal. 

A very hard white alloy of 77 parts of zinc, 17 of tin, and 6 of copper, 
is sometimes employed for the bearings of the driving-wheels of loco- 
motives. 

Iron and steel are coated with a closely adherent film of copper, by 
placing them in contact with metallic zinc in an alkaline solution of oxide 
of copper, prepared by mixing sulphate of copper with tartrate of potash 
and soda, and caustic soda. The copper is thus precipitated upon the 
iron by slow voltaic action, the zinc being the attacked metal. By 
adding a solution of stannate of soda to the alkaline copper solution, a 
deposit of bronze may be obtained. 

265. Oxides of Copper.' — Two oxides of copper are well known in the 
separate state, viz., the suboxide Cu 2 0, and the oxide CuO. Another 
oxide, Cu 4 0, has been obtained in a hydrated state, and there is some 
evidence of the existence of an acid oxide. 

The black oxide of copper {cupric oxide), CuO, is the black layer which 
is formed upon the surface of the metal when heated in air. It is employed 
by the chemist in the ultimate analysis of organic substances by com- 
bustion (page 84), being prepared for this purpose by acting upon copper 
with nitric acid to convert it into cupric nitrate (page 137), and heating 
this to dull redness in a rough vessel made of sheet copper, when it 
leaves the black oxide ; Cu(N0 3 ) 2 = 2N0 2 + + CuO. At a higher tem- 
perature the oxide fuses into a very hard mass; but it cannot be decom- 
posed by heat. Oxide of copper absorbs water easily from the air, but it 
is not dissolved by water ; acids, however, dissolve it, forming the salts 
of copper, whence the use of oil of vitriol and nitric acid for cleansing 
the tarnished surface of copper ; a blackened coin, for example, immersed 
in strong nitric acid, and thoroughly washed, becomes as bright as when 
freshly coined. Silica dissolves oxide of copper at a high temperature, 
forming cupric silicate, which is taken advantage of in producing a fine 
green colour in glass. 

Bed oxide or suboxide of copper (cuprous oxide), Cu 2 0, is formed when 
a mixture of 5 parts of the black oxide with 4 parts of copper filings 
is heated in a closed crucible. It may also be prepared by boiling a solu- 
tion of cupric sulphate with a solution containing sodium sulphite and 
sodium carbonate in equal quantities, when the suboxide of copper is 
precipitated as a reddish-yellow powder, which should be washed, by 
decantation, with boiled water; 2CuS0 4 + 2^a 2 C0 3 + Na 2 S0 3 = Cu 2 
+ 3Na 2 S0 4 + 2C0 2 . 

Cuprous oxide is a feeble base, but its salts are not easily ob- 
tained by direct action of acids, for these generally decompose it into 
metallic copper and cupric oxide yielding cupric salts. In the moist 
state it is slowly oxidised by the air. Ammonia dissolves cuprous 
oxide, forming a solution which is perfectly colourless until it is allowed 
to come into contact with air, when it assumes a fine blue colour, be- 
coming converted into an ammoniacal solution of cupric oxide. If the 
blue solution be placed in a stoppered bottle (quite filled with it) with a 
strip of clean copper, it will gradually become colourless, the cupric 
oxide being again reduced to cuprous oxide, a portion of the copper being 
dissolved. When copper filings are shaken with ammonia in a bottle of 
air, the same blue solution is obtained, the. oxidation of the copper being 



362 SULPHATE OF COPPEE. 

attended with a simultaneous oxidation of a portion of the ammonia, and 
its conversion into nitrous acid, so that the white fumes of ammonium 
nitrite are formed in the upper part of the bottle. If the blue solution be 
poured into a large quantity of water, a light blue precipitate of cupric 
hydrate is obtained. The ammoniacal solution of cupric oxide has the 
unusual property of dissolving paper, cotton, tow, and other varieties of 
cellulose, this substance being reprecipitated from the solution on adding 
an acid. 

Cuprous oxide, added to glass, imparts to it a fine red colour, which 
is turned to account by the glass-maker. 

Quadrant oxide of copper, Cu 4 0, has been obtained in combination with 
water, by the action of stannous chloride and potash upon a cupric salt. 

Cupric acid is believed to be formed when metallic copper is fused 
with nitre and caustic potash. The mass yields a blue solution in water, 
which is very easily decomposed with evolution of oxygen and precipita- 
tion of cupric oxide. The existence of an unstable oxide of copper, con- 
taining more than one atom of oxygen, is also rendered probable by the 
circumstance that oxide of copper acts like manganese dioxide in 
facilitating the disengagement of oxygen from potassium chlorate by heat 
(page 33). 

266. Sulphate of copper or cupric sidphate. — The beautiful prismatic 
crystals known as blue vitriol, blue stone, blue copperas, or sulphate of 
copper, have been already mentioned as formed in the preparation of 
sulphurous acid gas (page 199), by dissolving copper in oil of vitriol, a 
process which is occasionally employed for the manufacture of this salt. 
A considerable supply of the sulphate is obtained as a secondary product 
in the process of silver-refining (page 209). 

The sulphate of copper is also manufactured by roasting copper pyrites 
(FeCuS 2 ) with free access of air, when it becomes partly converted into a 
mixture of cupric sulphate with ferrous sulphate, FeCuS 2 + 8 = FeS0 4 
+ CuS0 4 . The ferrous sulphate, however, is decomposed by the heat, 
leaving ferric oxide (see page 322). When the roasted mass is treated 
with water, the ferric oxide is left undissolved, but the cupric sulphate 
enters into solution, and may be obtained in crystals by evaporation. 

These crystals, as they are found in commerce, are usually opaque, 
but if they are dissolved in hot water and allowed to crystallise slowly, 
they become perfectly transparent, and have then the composition 
expressed by the formula CuS0 4 .5H 2 0. If the crystals be heated to 
the temperature of boiling water, they lose four-fifths of their water, and 
crumble down to a greyish-white powder, which has the composition 
CuS0 4 .H 2 0, and if this be moistened with water, .it becomes very hot 
and resumes its original blue colour. The whitish opacity of the ordinary 
crystals of blue stone is due to the absence of a portion of the water of 
crystallisation. The fifth molecule of water can be expelled only at a 
temperature of nearly 400° F., and is therefore generally called water of 
constitution (see page 42), the formula of the crystals being then written 
CuS0 4 .H 2 0.4Aq. The crystals dissolve in 4 parts of cold and 2 parts 
of boiling water. The solution reddens litmus. 

The sulphate of copper' is largely employed by the dyer and calico- 
printer, and in the manufacture of pigments. It is also occasionally used 
in medicine, in the electrotype process, and in galvanic batteries. 

If a solution of cupric sulphate be mixed with an excess of solution 



CHLORIDES OF COPPER. 363 

of potash, a blue precipitate of cupric hydrate, Cu(OH) 2 , is produced. 
On boiling this in the liquid, it loses water and becomes black oxide. 
The paint known as blue verditer is cupric hydrate obtained by decom- 
posing cupric nitrate with calcium hydrate. 

When ammonia is added to solution of cupric sulphate, a basic sul- 
phate is first precipitated, which is dissolved by an excess of ammonia 
to a dark blue fluid. On allowing this to evaporate, dark blue crystals 
of ammonio-cuprics ulphate, CuS0 4 ,4NH 3 ,H 2 0, are deposited. They lose 
their ammonia when exposed to the air. 

A basic cupric sulphate, CuS0 4 ,4Cu(OH) 2 , constitutes the mineral 
brochantite. 

Sulphate of copper cannot easily be separated by crystallisation from 
the sulphates of iron, zinc, and magnesium, because it forms double salts 
with them, which contain, like those sulphates, seven molecules of water. 
An instance of this is seen in the black vitriol obtained from the mother- 
liquor of the sulphate of copper at Mansfeld, and forming bluish-black 
crystals isomorphous with green vitriol, FeS0 4 ,7H 2 0. The formula 
of black vitriol may be written (CuMgFeMnCoM)S0 4 .7H 2 0, the six 
isomorphous metals being interchangeable without altering the general 
character of the salt. 

Cupric arsenite or Scheele's green has been mentioned at page 241. 

The basic phosphates of copper compose the minerals tagilite and 
libethenite. 

The basic carbonates of copper have been noticed as forming the very 
beautiful minerals blue malachite, or chessylite, and green malachite. 

Mineral green, CuC0 3 .Cu(OH) 2 , has the same composition as green 
malachite, and is prepared by mixing hot solutions of sodium carbonate 
and cupric sulphate. When boiled in the liquid, it is gradually con^ 
verted into black oxide of copper. 

Silicates of copper are found in the minerals dioptase, or emerald copper, 
and chrysocolla. 

267. Chlorides of copper. — The chloride of copper {cupric chloride) 
(CuCl 2 ) is produced by the direct union of its elements, when it forms a. 
brown mass, which fuses easily, and is decomposed into chlorine and sub- 
chloride of copper, the latter being afterwards converted into vapour. 
When dissolved in water, it gives a solution which is green when concen- 
trated, and becomes blue on dilution. The hydrated cupric chloride is 
readily prepared by dissolving the black oxide in hot hydrochloric acid, 
and allowing the solution to crystallise; it forms green needle-like 
crystals (CuCl 2 .2H 2 0) which become blue when dried in vacuo (Hartley). 
A solution of chloride of copper in alcohol burns with a splendid green 
flame, and the chloride imparts a similar colour to a gas flame. 

Oxychloride of copper (CuCl 2 .3Cu0.4H 2 0) is found at Atacama, in 
prismatic crystals, and is called atacamite. The paint Brunswick green 
has the same composition, and is made by moistening copper with solu- 
tion of hydrochloric acid or sal-ammoniac, and exposing it to the air in 
order that it may absorb oxygen; Cu 4 + 2HCl + 3H 2 + 4 = CuCl. 2 . 
3Cu0.4H 2 0. The Brunswick green of the shops frequently consists of a 
mixture of Prussian blue, chromate of lead, and sulphate of baryta. 

Subchloride of copper (cipi-ous chloride), Cu 2 Cl 2 , is formed when fine 
copper turnings are shaken with strong hydrochloric acid in a bottle of 



364 COPPER AND SULPHUR. 

air (Cu 2 + 2HCl + = Cu 2 Cl 2 + H 2 0). The subchloride dissolves in the 
excess of hydrochloric acid, forming a brown solution, from which water 
precipitates the white subchloride of copper, for this is one of the few 
chlorides insoluble in water. When exposed to light it assumes a 
purplish-grey tint. It may be obtained in larger quantity by dissolving 
5 parts of black oxide of copper in hydrochloric acid, and boiling with 
4 parts of fine copper turnings, the brown solution being afterwards pre- 
cipitated by water. If the solution be moderately diluted and set aside, 
it deposits tetrahedral crystals of the subchloride. Ammonia (free from 
air) dissolves the subchloride to a colourless liquid, which becomes dark 
blue by contact with air, absorbing oxygen. The ammoniacal solution of 
cuprous chloride is employed as a test for acetylene (page 93), which 
gives a red precipitate with it. The solution may be preserved in a 
colourless state by keeping it in a well-stoppered bottle, quite full, with 
strips of clean copper. "When copper, in a finely-divided state, is boiled 
with solution of ammonium chloride, the solution deposits colourless 
crystals of the salt, Cu 2 Cl 2 (NH 3 ) 2 . If the solution of this salt be exposed 
to the air, blue crystals are deposited, having the formula Cu 2 Cl 2 .Cu Cl 2 . 
4NH 3 .H 2 0, and on further exposure, a compound of this last salt with 
ammonium chloride is deposited. The solution of subchloride of copper 
in hydrochloric acid is employed for absorbing carbonic oxide in the 
analysis of gaseous mixtures. When this solution is exposed to air it 
absorbs oxygen, and deposits the oxychloride of copper. A strong solu- 
tion of ammonium or potassium chloride readily dissolves the cuprous 
chloride, even in the cold, forming soluble double chlorides. The solution 
in potassium chloride does not absorb oxygen quite so easily as that in 
ammonium chloride. 

268. Sulphides of copper. — Copper has a very marked attraction for 
•sulphur, even at the ordinary temperature. A bright surface of copper 
soon becomes tarnished by contact with sulphur, and hydrosulphuric acid 
blackens the metal. Finely-divided copper and sulphur combine slowly 
at the ordinary temperature, and when heated together, they combine with 
combustion. A thick copper wire burns easily in vapour of sulphur' 
(page 193). Copper is even partly converted into sulphides when boiled 
with sulphuric acid, as in the preparation of sulphurous acid gas. This 
great attraction of copper for sulphur is taken advantage of in the process 
of kernel roasting for extracting the copper from pyrites containing as 
little as 1 per cent, of the metal. The pyrites is roasted in large heaps 
(page 190) for several weeks, when a great part of the iron is converted 
into peroxide, and the copper remains combined with sulphur, forming 
a hard kernel in the centre of the lumps of ore. This kernel contains 
about 5 per cent, of copper, and can be smelted with economy. Children 
are employed to detach the kernel from the shell, which consists of 
peroxide of iron and a little sulphate of copper, which is washed out 
with water. 

The subsulphide of copper or cuprous sulphide (Cu 2 S) has been mentioned 
among the ores of copper. and among the furnace products in smelting, 
when it is sometimes obtained in octahedral crystals. It is not attacked 
by hydrochloric acid, but nitric acid dissolves it readily. Copper pyrites 
is believed to contain the copper in the form of cuprous sulphide, its true 
formula being Cu 2 S.Fe 2 S 3 ; for if the copper be present as cupric sulphide, 



CHARACTERS OF LEAD. 365 

CuS, the iron must be present as ferrous sulphide, and the mineral would 
have the formula CuS.FeS. Now, FeS is easily attacked by dilute sul- 
phuric or hydrochloric acid, which is not the case with copper pyrites. 
Nitric acid, however, attacks it violently. 

Sulphide of copper or cupric sulphide (CuS) occurs in nature as indigo 
copper or blue copper, and may be obtained as a black precipitate by the 
action of hydrosulphuric acid upon solution of cupric sulphate. "When 
this precipitate is boiled with sulphur and ammonium sulphide, it is 
dissolved in small quantity, and the solution on cooling deposits fine 
scarlet needles containing a higher sulphide of copper combined with 
sulphide of ammonium. 

A pentasulphide of copper (CuS 5 ) is obtained by decomposing cupric 
sulphate with potassium pentasulphide; it forms a black precipitate dis- 
tinguished from the other sulphides of copper by its solubility in potassium 
carbonate. 

The sulphides of copper, when exposed to air in the presence of water, 
are slowly oxidised and converted into cupric sulphate, which is dissolved 
by the water. It appears to be in this way that the blue water of the 
copper mines is formed. 

Phosphide of copper, cupric pjJiosphide (Cu 3 P 2 ), obtained as a black 
powder by boiling solution of cupric sulphate with phosphorus, has been 
already mentioned as a convenient source of phosphine. Another phos- 
phide, obtained by passing vapour of phosphorus over finely-divided copper 
at a high temperature, is employed in Abel's composition for magneto- 
electric fuzes, in conjunction with cuprous sulphide and potassium 
chlorate. 

Silicon may be made to unite with copper by strongly heating finely- 
divided copper with silica and charcoal. A "bronze-like mass is thus 
obtained containing about 5 per cent, of silicon. It is said to rival iron 
in ductility and tenacity, and fuses at about the same temperature as 
bronze. 

LEAD. 

Pb" -. 207 parts by weight. 

269. Lead owes its usefulness in the metallic state chiefly to its soft- 
ness and fusibility. The former quality allows it to be easily rolled into 
thin sheets, and to be drawn into the form of tubes or pipes; it is indeed 
the softest of the metals in common use, and at the same time the least 
tenacious, so that it can only be drawn with difficulty into thin wire, and 
is then very easily broken. The ease with which it makes a dark streak 
upon paper shows how readily minute particles of the metal may be 
abraded. Its want of elasticity also recommends it for some special uses, 
as for deadening a shock or preventing a rebound. 

In fusibility it surpasses all the other metals commonly employed in 
the metallic state, except tin, for it melts at 617° F., and this circumstance, 
taken in conjunction with its high specific gravity (11*4), particularly 
adapts it for the manufacture of shot and bullets. For one of its extensive 
uses, however, as a covering for roofs, it would be better suited if it were 
lighter and less fusible, for in case of fire in houses so roofed, the fall of 
the molten lead frequently aggravates the calamity. 

With the exception, perhaps, of the ores of iron, none is more abundant 
in this country than the chief ore of lead, galena, a sulphide of lead (PbS). 



ZM 



SMELTING LEAD ORES. 



This ore might at the first glance he mistaken for the metal itself, from its 
high specific gravity and metallic lustre. It is found forming extensive 
veins in Cumberland, Derbyshire, arid Cornwall, traversing a limestone 
rock in the two first counties, and. a clay slate in the last. Spain also 
furnishes large supplies of this important ore. 

Galena presents a beautiful crystalline appearance, being often found in 
large isolated cubes, which readily cleave or split up in directions parallel 
to their faces. Blende (sulphide of zinc) and copper pyrites (sulphide of 
copper and iron) are frequently found in the same vein with galena, and 
it is usually associated with quartz (silica), heavy spar (barium sulphate), 
or fluor spar (calcium fluoride). Considerable quantities of sulphide of 
silver are often present in galena, and in many specimens the sulphides of 
bismuth and antimony are found. 

Though the sulphide is the most abundant natural combination of lead, 
it is by no means the only form in which this metal is found. The metal 
itself is occasionally met with, though in very small quantity, and the 
carbonate of lead (PbC0 3 ), wliite lead ore, forms an important ore in the 
United States and in Spain. The sulphate of lead, anglesite (PbS0 4 ), is 
also found in Australia, and is largely imported into this country to be 
smelted. 

270. The extraction of lead from galena is effected by taking advantage 
of the circumstance, that when a combination of a metal with oxygen is 
raised to a high temperature in contact with a sulphide of the same metal, 
the oxygen and sulphur unite, and the metal is liberated. 

The ore, having been separated by mechanical treatment as far as pos- 
sible from the foreign matters associated with it, is mixed with a small 
proportion of lime, and spread over the hearth of a reverberatory furnace 
(fig. 261), the sides of which are considerably inclined towards the centre, 
so as to form a hollow for the reception of the molten lead. 




Fig. 261. — Furnace for smelting lead ores. 

During the first stage of the smelting process, the object is to roast the 
ore with free access of air, exposing as large a surface as possible, on which 
account the temperature is' kept below that at which galena fuses; indeed, 
during the first two hours, no fuel is thrown into the grate, sufficient heat 
being radiated from the sides of the furnace, which have become red hot 
during the smelting of the previous charge of ore. The ore is stirred from 



SMELTING OF GALENA. 367 

time to time, to expose fresh, surfaces to the action of the atmospheric 
oxygen. 

The effect of this roasting is to convert a portion of the sulphide of lead 
(PbS) into sulphate of lead (PbS0 4 ), whilst another portion loses its 
sulphur, which is evolved as sulphurous acid gas (S0 2 ), and acquires 
oxygen in its stead, becoming converted into oxide of lead (PbO). A 
large proportion of the galena, however, remains unoxidised. When the 
roasting is sufficiently advanced, some fuel is thrown into the grate, some 
rich slags from previous smeltings are thrown on to the hearth, the 
damper is slightly raised, and the doors of the furnace are closed, so that 
the charge may be heated to the temperature at which the oxide and sul- 
phate of lead act upon the unaltered sulphide, furnishing metallic lead, 
whilst the sulphur is expelled in the form of sulphurous acid gas — 

PbS + 2PbO = Pb 3 + S0 2 , and PbS0 4 + PbS = Pb 2 + 2S0 2 . 

During this part of the operation the contents of the hearth are con- 
stantly raked up towards the fire-bridge, so as to facilitate the separation 
of the lead, and to cause it to run down into the hollow provided for its 
reception. It is also found that the separation of the lead from the slags 
is much assisted by occasionally throwing open the doors to chill the 
furnace. After about four hours the charge is reduced to a pretty fluid 
condition, the lead having accumulated at the bottom of the depressed 
portion of the hearth with the slag above it ; this slag consists chiefly of 
the silicates of lime and oxide of lead, and would have contained a larger 
proportion of the latter if the lime had not been added as a flux at the 
commencement of the operation. In order still further to reduce the 
quantity of lead in the slag, a few more shovelfuls of lime are now thrown 
into the hearth, together with a little small coal, the latter serving to 
reduce to the metallic state the oxide of lead displaced by the lime from 
its combination with the silica. 

But since silicate of lime is far less fusible than silicate of oxide of 
lead, the effect of this addition of lime is to dry up the slags to a 
semi-solid mass, and it will now be seen that if the whole of the lime had 
been added at the commencement of the smelting, the diminished fusibility 
of the slag would have opposed an obstacle to the separation of the metallic 
lead. 

During the last hour or so the temperature is very considerably raised, 
and at the expiration of about six hours, when the greater portion of the 
lead is thought to have separated, the slag is raked out through one of the 
doors of the furnace, and the melted metal allowed to run out through a 
tap-hole in front of the lowest portion of the hearth, iato an iron basin, 
from which, it is ladled into pig-moulds. 

The rich slags, together with the layer of subsulphide of lead (Pb 2 S) 
which forms over the surface of the metal, are worked up again with a 
fresh charge of ore. 

In the smelting of galena a very considerable quantity of lead is carried 
off in the form of vapour; and in order to condense this, the gases from 
the furnace are made to pass through flues, the aggregate length of 
which is sometimes three or four miles, before being allowed to escape up 
the chimney. When these flues are swept, many tons of lead are recovered 
in the forms of oxide and sulphide. 

In the north of England the smelting of lead ores is now generally 



168 



TREATMENT OF HARD LEAD. 



conducted in an economico-furnace (fig. 262), or small blast-furnace, instead 
of in the reverberatory furnace described above. Air is supplied to the 
furnace through three blast-pipes (A), and the ore and fuel being charged 
in at B, the lead runs into a cavity (C) at the bottom of the furnace, 
whilst the slag flows over into a reservoir (D) outside the furnace. The 
charge is sprinkled with water through the rose (E) fixed just above the 
opening into the chimney (F), to prevent it from being blown away by. 
the current of air. 

271. Some varieties of lead, particularly those smelted from Spanish ores, 
are known as hard lead, their hardness being chiefly due to the presence 
of antimony ; and since this hardness interferes materially with some of the 
uses of the metal, such lead is generally subjected to an improving or cal- 
cining process, in which the impurities are oxidised and removed, together 
with a portion of the lead, in the dross. * To effect this, 6 or 8 tons 
of the hard lead are fused in an iron pot (P, fig. 263), and transferred to 




Fig. 263. 

a shallow cast-iron pan (C) measuring about 10 feet by 5. In this pan, 
which is set in the hearth of a reverberatory furnace, and is about 8 
inches deep nearest the grate and 9 inches at the other end, the lead 
is kept in fusion by the flame which traverses it from the grate G to the 
flue F, for a period varying with the degree of impurity, some specimens 
being found sufficiently soft after a single day's calcination, whilst others 

* The following analyses illustrate the composition of hard lead : — 





English. 


Spanish. 


Lead, .... 

Antimony, 

Copper, . . . 

Iron, .... 


99-27 
0-57 
0-12 
0-04 


95-81 
3-36 
0-32 
0-21 


100-00 100-00 



pattinson's desilverizing peocess. 369 

must be kept in a state of fusion for three or four weeks. The workman 
judges of the progress of the operation by a peculiar flaky crystalline 
appearance assumed by a small sample on cooling. When sufficiently 
purified, the metal is run off and cast into pigs. 

At first sight, it is not intelligible how antimony should be removed 
from lead by calcination, since lead is the more easily oxidised metal. 
The result must be ascribed to the tendency of antimony to form antimonic 
oxide (Sb 2 5 ), which combines with the oxide of lead. The dross 
(antimoniate of lead) formed in this process, when reduced to the metallic 
state, yields an alloy of lead with 30 or 40 per cent, of antimony, which 
is much used for casting type furniture for printers. 

272. Extraction of silver from lead. — The lead extracted from galena 
often contains a sufficient quantity of silver to allow of its being pro- 
fitably extracted. Previously to the year 1829, this was practicable only 
when the lead contained more than 1 1 ounces of silver per ton, for the 
only process then known for effecting the separation of the two metals 
was that of cupellation, which necessitates the conversion of the whole 
of the lead into oxide, which is then to be separated from the silver 
and again reduced to the metallic state, thus consuming so large an 
amount of labour that a considerable yield of silver must be obtained to 
pay for it. 

By the simple and ingenious operation known as Pattinson's desilverising 
process, a very large amount of the lead can be at once separated in the 
metallic state with little expenditure of labour, thus leaving the remainder 
sufficiently rich in the more precious metal to defray the cost of the far 
more expensive process of cupellation, so that 3 or 4 ounces of silver per 
ton can be extracted with profit. Pattinson founded his process upon the 
observation that when lead containing a small proportion of silver is 
melted and allowed to cool, being constantly stirred, a considerable 
quantity of the lead separates in the form of crystals containing a very 
minute proportion of silver, almost the whole of this metal being left 
behind in the portion still remaining liquid. 

Eight or ten cast-iron pots, set in brickwork, each capable of holding 
about 6 tons of lead, are placed in a row, with a fire-place underneath 
each of them (fig. 264). Suppose that there are ten pots numbered 
consecutively, that on the extreme left of the workman being ]STo. 1, and 
that on his extreme right No. 10. About 6 tons of the lead containing 
silver are melted in pot No. 5, the metal skimmed, and the fire raked out 
from beneath so that the pot may gradually cool, its liquid contents being 
constantly agitated with a long iron stirrer. As the crystals of lead form, 
they are well drained in a perforated ladle (about 10 inches wide and 5 
inches deep) and transferred to pot No. 4. When about ^ths of the 
metal have thus been removed in the crystals, the portion still remaining 
liquid, which retains the silver, is ladled into pot No. 6, and the pot No. 
5, which is now empty, is charged with fresh argentiferous lead to be 
treated in the same manner. 

When pots Nos. 4 and 6 have received, respectively, a sufficient quantity 
of the crystals of lead and of the liquid part rich in silver, their contents 
are subjected to a perfectly similar process, the crystals of lead being 
always passed to the left, and the rich argentiferous alloy to the right. 
As the final result of these operations, the pot No. 10, to the extreme 
right, becomes filled with a rich alloy of lead and silver, sometimes 

2 a 



370 



CUPELLATION OF ARGENTIFEROUS LEAD. 



containing 300 ounces of silver to the ton, whilst pot No 1, to the extreme 
left, contains lead in which there is not more that J ounce of silver to the 
ton. This lead is cast into pigs for the market. The ladle used in the 
above operation is kept hot by a small temper pot containing melted lead. 
A fulcrum is provided at the edge of each pot, for resting the ladle 
during the shaking of the crystals to drain off the liquid metal. Any 
copper present in the lead is also left with the silver in the liquid 
portion. 




Fig. 264. — Pattinson's desilverising process. 

273. In order to extract the silver from the rich alloy, it is subjected 
to a process of refining, or cupellation, which is founded upon the 
oxidation suffered by lead when heated in air, and upon the absence of 
any tendency on the part of silver to combine directly with oxygen. 

The refinery or cupelling furnace (fig. 265), in which this operation is 
performed, is a reverberatory fu'rnance, the hearth of which consists of a 
cupel (C), made by ramming moist powdered bone-ash mixed with a little 
wood -ask into an oval iron frame about 4 inckes deep, and provided witk 
four cross-bars at tke bottom, eack about 4 inckes wide. Wken tkis frame 
kas been well filled witk bone-ask, part of it is scooped out, so as to leave 
tke sides about 2 inckes tkick at tke top and 3 inckes at the bottom, the 
bone-ash being left about 1 inck tkick above tke iron cross-bars. 

Tke cupel, wkick is about 4 feet long by 2| feet wide, is fixed so that 
tke flame from tke grate (G) passes across it into tke ckimney (B), and at 
one end, tke nozzle (N) of a blowing apparatus directs a blast of air over 
tke surface of tke contents of tke cupel. Tke latter is carefully dried by 
a gradually increasing keat, and is then keated to redness ; tke alloy of 
lead and silver, kaving been previously melted in an iron pot (P) fixed 



PROCESS OF CUPELLATION. 



371 



by the side of the furnace, is ladled in through a gutter until the cupel 

is nearly filled with it ; a film of oxide soon makes its appearance upon 

the surface of the lead, and is fused by the high temperature. When the 

blast is directed upon the surface, it blows off this film of oxide, and 

supplies the oxygen for the formation of another film upon the clean 

metallic surface thus exposed. A part of the oxide of lead or litharge 

thus formed is at first absorbed _ 

by the porous material of the pf"^" 1 ;'^ 

cupel, but the chief part of it is 

forced by the blast through a 

channel cut for the purpose in 

the opposite end to that at which 

the blast enters, and is received 

as it issues from A, in an iron 

vessel placed beneath the furnace. 

In proportion as the lead is in 

this manner removed from the 

cupel, fresh portions are supplied 

from the adjoining melting-pot, 

and the process is continued 

until about 5 tons of the alloy 

have been added. 

The cupellation is not con- 
tinued until the whole of the 
lead has been removed, but until 
only 2 or 3 cwts. of that metal 
are left in combination with the 
whole of the silver (say 1000 
ounces) contained in the 5 tons of 
alloy. The metal is run through 
a hole made in the bottom 
of the cupel, which is then again stopped up so that a fresh charge may 
be introduced. The fumes of oxide of lead which are freely evolved 
during this process are carried off by a hood and chimney (H) situated 
opposite to the blast of air. 

When three or four charges have been cupelled, so as to yield from 
3000 to 5000 ounces of silver alloyed with 6 or 8 cwts. of lead, the removal 
of the latter metal is completed in another cupel, since some of the silver 
is carried off with the last portions of litharge. The appearances indicat- 
ing the removal of the last portion of lead are very striking ; the surface 
of the molten metal, which has been hitherto tarnished, becomes iridescent 
as the film of oxide of lead thins off, and afterwards resplendently bright, 
and when the cake of refined silver is allowed to cool, it throws up from 
its surface a variety of fantastic arborescent excrescences, caused by the 
escape of oxygen which has been mechanically absorbed by the fused 
silver, and is given off during solidification. 

The litharge obtained from the cupelling furnaces is reduced to the 
metallic state by mixing it with small coal, and heating it in a furnace 
similar to that employed in smelting galena. 

A new process for desilverising lead consists in melting about 18 tons 
of the rich lead in a cast-iron pot, and stirring it with about 1 per cent, 
of zinc for twenty minutes ; on standing, the zinc rises to the surface, 




Fig. 265. — Cupellation furnace. 



372 



USES OF LEAD. 




bringing with it the silver and some lead, forming a solid crust, which is 
removed and distilled in a plumbago crucible to recover the zinc. The 
rich alloy of silver and lead remaining in the crucible is cupelled in the 
usual way. The desilverised lead is freed from zinc by the improving 
process (p. 368). 

274. On the small scale, lead may easily be extracted from galena by mixing 300 
grains with 450 grains of dried carbonate of soda and 20 grains of charcoal, intro- 
ducing the mixture into a crucible, and placing in it two tenpenny nails, heads down- 
wards. The crucible is covered and heated in a moderate tire for about half an hour. 
(A charcoal fire in the small furnace, fig. 131, page 117, will suffice.) The remainder 
of the nails is carefully removed from the liquid mass, which is then allowed to cool, 
the crucible broken, and the lead extracted and weighed. In this process the 
sulphur of the galena is removed, partly by the sodium of the carbonate and partly 
by the iron of the nails, the excess of carbonate of soda serving to flux any silica 
with which the galena may be mixed. 

Or 300 grs. of galena may be mixed w r ith 600 grs. of sodium carbonate and 200 
grs. of nitre (which oxidises the sulphur), and fused for half an hour. 

To ascertain if it contains silver, the button of lead is 
placed on a small bone-ash cupel (fig. 266), heated in a 
muffle (fig. 267), until the whole of the lead is oxidised 
and absorbed into the bone-ash of the cupel, leaving the 
minute globule of silver. 

Small globules of lead may be conveniently cupelled 
on charcoal before the blowpipe, by pressing some 
bone-ash into a cavity scooped in the charcoal, placing the lead upon its surface, 
and exposing it to a good oxidising flame (page 109) as long as it decreases in size. 
If any copper be present, the bone-ash will show a green stain after cooling. Pure 
lead gives a yellow stain. 

275. Uses of lead. — The employment of this metal for roofing, &c, 
has been already noticed. Its fusibility adapts it for casting type for 

printing, but it would be far too soft for 
this purpose; accordingly, type-metal con- 
sists of an alloy of 4 parts of lead with 1 of 
antimony. A similar alloy is used for the 
bullets contained in shrapnel shells, since 
bullets of soft lead would be liable to be 
jammed together, and would not scatter so 
well on the explosion of the shell. On the 
other hand, rifle bullets are made of very 
pure soft lead, in order that they may more 
easily take the grooves of the rifle. 

Small shot are made of lead to which 
about 40 lbs. of arsenic per ton has been 
added. The arsenic dissolves in the lead, 
hardening it and causing it to form spherical 
drops when chilled. The fluid metal is 
poured through a sort of colander fixed at 
the top of a lofty tower (or at the mouth of 
a deserted coal shaft), and the minute drops 
into which it is thus divided are allowed to 
fall into a vessel of water, after having been 
chilled by the air in their descent. They 
are afterwards sorted, and polished in revolv- 
plumbago. If too little arsenic is employed, the 
shot are elongated or pyriform; and if the due proportion has been 
exceeded, their form is flattened or lenticular. 




Fig. 267. 



ing barrels containin 



OXIDES OF LEAD. 373 

Common solder is an alloy of equal weights of lead and tin. which is 
more fusible than either metal separately. Other alloys containing lead 
will be noticed in their proper places. 

Leaden vessels are much used in manufacturing chemistry, on account 
of the resistance of this metal to the action of acids. Xeither concentrated 
sulphuric,* hydrochloric,, nitric, or hydrofluoric acid will act upon lead 
at the ordinary temperature. The best solvent for the metal is nitric 
acid of sp. gr. 1 "2, since the nitrate of lead, being insoluble in an acid of 
greater strength, would be deposited upon the metal, which it would 
protect from further action. 

Lead is easily corroded in situations where it is brought in contact 
with air highly charged with carbonic acid gas, when it absorbs oxygen, 
forming oxide of lead, which combines with carbonic acid gas and water 
to produce the basic carbonate of lead, PbC0 3 ,Pb(OH) 2 . The lead of old 
coffins is often found converted into a white earthy-looking brittle mass 
of basic carbonate, with a very thin film of metallic lead inside it. 

When lead is exposed to the joint action of air and of the acetic acid 
contained in beer, wine, cider, &c, it becomes converted into acetate of 
lead or sugar of lead, which is very poisonous. Hence the accidents 
arising froni the reprehensible practice of sweetening cider by keeping 
it in contact with lead, and from the accidental presence, in beer and 
wine bottles, of shot which have been employed in cleansing them. The 
action of water upon leaden cisterns has been already noticed. Contact 
with air and sea-water soon converts lead into oxide and chloride. 

276. Oxides of Lead. — Four compounds of lead with oxygen are 
known — 

Suboxide of lead, Pb,0 | Red oxide of lead, Pb 3 4 
Oxide „ PbO Peroxide „ Pb0 2 

The bright surface of lead soon tarnishes when exposed to the air, 
becoming coated with a dark film, which is believed to consist of suboxide 
of lead. In a very finely-divided state, lead takes 
fire when thrown into the air, and is converted K2 
into oxide of lead. 

The lead pyroplwrus, for exhibiting the spontaneous 
combustion of lead, is prepared by placing some lead 
tartrate in a glass tube closed at one end (fig. 268), 
drawing the tube out to a narrow neck near the open end, 
and holding it nearly horizontally, whilst the lead tartrate 
is heated with a gas or spirit flame as long as any fames 
are evolved ; the neck is then fused with a blowpipe 
flame and drawn off. Lead tartrate (PbC 4 H 4 6 ), when 
heated, leaves a mixture of metallic lead with charcoal, Fig. 268. 

which prevents it from fusing into a compact mass. 

This mixture may be preserved unchanged in the tube for any length of time ; but 
when the neck is broken off and the contents scattered into the air, they inflame at 
once, producing thick fumes of oxide of lead. Lead tartrate is prepared by adding 
solution of lead acetate to solution of tartaric acid constantly stirred, as long as a 
precipitate is formed. The precipitated lead tartrate is collected upon a filter, washed 
several times, and dried at a gentle heat. 

Oxide or protoxide of lead (plumbous ocride) is prepared on a large scale 
by heating lead in air. When the metal is only moderately heated, the 

* It has recently been found that pure lead is slowly acted on by sulphuric acid, hydrogen 
being evolved. The presence of a little antimony almost entirely prevents the action. 




374 KED LEAD. 

oxide forms a yellow powder, which is known in commerce as massicot, 
but at a higher temperature the oxide melts, and on cooling forms a 
brownish scaly mass which is called litharge (\i6o<s, stone; apyvpos, silver), 
probably because that obtained by the alchemists would always furnish a 
considerable proportion of silver, which was present in most samples of lead 
before the introduction of Pattinson's process. The litharge of commerce 
often has a red colour, caused by the presence of some red oxide of lead; 
from 1 to 3 per cent, of finely-divided metallic lead may also sometimes 
be found in it. When heated to dull redness, litharge assumes a dark 
brown colour, and becomes yellow on cooling. At a bright red heat it fuses, 
and readily attacks clay crucibles, forming a fusible silicate of lead, and 
soon perforating the sides. "When boiled with distilled water, litharge is 
dissolved in small quantity, yielding a solution which is decidedly alka- 
line, and becomes turbid when exposed to the air, absorbing carbonic 
acid gas, and depositing lead carbonate. The presence of a small quantity 
of saline matter in the water hinders the solution of the oxide, but 
organic matter, and especially sugar, favours it. Two definite white 
hydrates of oxide of lead, H 2 0.2PbO and H 2 0.3PbO, may be obtained by 
precipitating solutions of lead with the alkalies. Oxide of lead is a 
powerful base, and has a strong tendency to form basic salts. Hot solu- 
tions of potash and soda dissolve it readily, and deposit it in pink crystals 
on cooling. 

Litharge, from its easy combination with silica at a high temperature, is 
much used in the manufacture of glass and in glazing earthenware. The 
assayer also employs it as a flux. A mixture of litharge with lime is 
sometimes applied to the hair, which it dyes of a purplish-black colour, 
due to the formation of sulphide of lead from the sulphur existing in hair. 
Dhil mastic, used by builders in repairing stone, is a mixture of 1 part of 
massicot with 10 parts of brick-dust, and enough linseed oil to form a 
paste; it sets into a very hard mass, which is probably due partly to the 
formation of silicate of lead, and partly to the drying of the linseed oil by 
oxidation favoured by the oxide of lead. 

Red lead or minium is prepared by heating massicot in air to about 
600° F., when it absorbs oxygen, and becomes converted into red lead: 
The massicot for this purpose is prepared by heating lead in a rever- 
beratory furnace to a temperature insufficient to fuse the oxide which is 
formed, and rejecting the first portions, which contain iron and other 
metals more easily oxidisable than lead (as cobalt), as well as the last, 
which contain copper and silver, less easily oxidised than lead. The inter- 
mediate product is ground to a fine powder and suspended in water ; the 
coarser particles are thus separated from the finer,, which are dried, and 
heated on iron trays placed in a reverberatory furnace, till the requisite 
colour has been obtained. Minium is largely used in the manufacture of 
glass, whence it is necessary that it should be free from the oxides of iron, 
copper, cobalt, &c, which would colour the glass. It is also employed as 
a common red mineral colour, and in the manufacture of lucifer matches. 

When minium is treated with dilute nitric acid, lead nitrate Pb(N0 3 ) 2 
is obtained in solution, and peroxide of lead (Pb0. 2 ) is left as a brown 
powder, showing that minium is probably a compound of the oxide and 
peroxide of lead. The minium obtained by heating massicot in air till no 
further increase of weight is observed, has the composition 2PbO.Pb0 2 
or Pb 3 4 , which would appear to represent pure minium ; commercial 



WHITE LEAD. 375 

minium, however, has more frequently a composition corresponding to 
3PbO.Pb0 2 , but when this is treated with potash, PbO is dissolved out, 
and 2PbO.Pb0 2 remains. Minium evolves oxygen at a red heat, becoming 
PbO, hence the necessity for keeping the temperature below 600° F. 
during its preparation. 

Peroxide, or binoxide, or puce oxide of lead {plumbic oxide)) is found in 
the mineral kingdom as heavy lead ore, forming black, lustrous, six-sided 
prisms. It may be prepared from red lead by boiling it, in fine powder, 
with nitric acid diluted with five measures of water, washing and drying. 
The binoxide of lead easily imparts oxygen to other substances • sulphur, 
mixed with it, may be ignited by friction, hence this oxide is a common 
ingredient in lucifer-match compositions. Its oxidising property is 
frequently turned to account in the laboratory ; for example, in absorbing 
sulphur dioxide from gaseous mixtures by converting it into sulphate of 
lead ; Pb0 2 + S0 2 = PbS0 4 . Binoxide of lead is not dissolved by dilute 
acids, and has no basic properties ; indeed, it is sometimes called plumbic 
anhydride, for it acts upon potassium hydrate, yielding potassium plumbate 
(K 2 Pb0 3 .3H 9 0), which has been crystallised from an alkaline solution, 
but is decomposed by pure water. 

277. White lead or ceruse is a carbonate of lead, or, strictly speaking, a 
basic carbonate, a combination of lead carbonate, PbC0 3 , with variable 
proportions of lead hydrate, Pb(OH) 2 . This substance is a constant product 
of the corrosive action of air and water upon the metal. Its formation is, of 
course, very much encouraged by the presence of organic matters in a state 
of decay, which evolve carbonic acid gas. 

"White lead is manufactured on the large scale by two processes, which 
depend, however, upon the same principle ; this may be stated as follows : — 
When oxide of lead is brought in contact with acetic acid (H.C 2 H 3 2 ), 
it forms lead acetate (sugar of lead) Pb(C 2 H 3 2 ) 2 . This salt is capable of 
combining with two molecules of lead oxide, forming the tribasic lead acetate, 
Pb(C 2 H 3 2 ). 2 .2PbO, and if this be acted upon by carbonic acid gas, the 
lead oxide is converted into carbonate, whilst the normal lead acetate, 
Pb(C 2 H 3 2 ) 2 , is left. 

In the older of the two processes, commonly known as the Dutch pro- 
cess, metallic lead, in the form of square gratings cast from the purest 
lead, is placed over earthen pots containing a small quantity of common 
vinegar ; a number of these pots being built up into heaps, together with 
alternate layers of dung or spent tan, the heaps are entirely covered up 
with the same material. The metal is thus exposed to conditions most 
favourable to its oxidation, viz., a very warm and moist atmosphere pro- 
duced by the fermentation of the organic matters composing the heap, and 
the presence of a large quantity of acid vapour generated from the acetic 
acid of the vinegar. The lead is therefore soon converted into oxide, a 
portion of which unites with the acetic acid to form the tribasic acetate of 
lead, which is then decomposed by the carbonic acid gas, evolved from 
the fermenting dung or tan, yielding carbonate of lead, which combines 
with another portion of the oxide of lead and of water to form the white 
lead. The neutral acetate of lead left after the removal of the oxide of 
lead from the tribasic acetate, is now ready to take up an additional quan- 
tity of the oxide, and the process is thus continued until, in the course of 
a few weeks, the lead has become coated with a very thick crust of white 



376 CHLORIDE OF LEAD. 

lead ; the heaps are then destroyed, the crust detached, washed, to remove 
adhering acetate of lead, ground to a paste with water, and dried. Rolled 
lead is not so easily converted as cast lead. 

The newer process is a more direct application of the same principle, 
for it consists in boiling acetic acid with an excess of litharge in order to 
produce the tribasic acetate of lead, which is afterwards decomposed by 
passing through it a current of carbonic acid gas obtained by combustion 
or fermentation, or even by exhalation from the earth. The solution of 
neutral acetate of lead is then again boiled with litharge, when tribasic 
acetate is produced, and is again precipitated by the carbonic acid gas. 
The precipitated carbonate of lead always carries down with it a variable 
proportion of the hydrate of lead. This process is, of course, much more 
rapid than the old one, and dispenses with the grinding, which is so in- 
jurious to the workmen ; but the white lead so produced, being crystalline, 
has less opacity or covering-power {body) than that obtained by the Dutch 
method. 

The usual composition of w T hite lead is expressed by the formula 
Pb(OH) 2 .2PbC0 3 , though other basic carbonates of lead are often mixed 
with it. 

White lead being very poisonous, its use by painters and others is gene- 
rally attended with symptoms of lead poisoning, arising in many cases, 
probably, from neglecting to wash the hands before eating, the effect of 
lead being cumulative, so that minute doses may show their combined 
action after many days. Diluted sulphuric acid and solutions of the sul- 
phates of magnesia and the alkalies are sometimes taken internally to 
counteract its effect, since the sulphate of lead is not poisonous. 

All paints containing lead, and cards glazed with white lead, are 
blackened even by minute quantities of sulphuretted hydrogen, from the 
production of black sulphide of lead. If the blackened surface remain 
exposed to the light and air, it is bleached again, the sulphide of lead 
(PbS) being oxidised and converted into white sulphate of lead (PbS0 4 ), 
but this does not take place in the dark. A little sulphide of lead or 
powdered charcoal is sometimes mixed with commercial white lead to give 
it a bluish tint. 

The pure lead carbonate is found in white crystals associated with galena. 

Lead sulphate is found in nature in prismatic and octahedral crystals 
of anglesite or lead-vitriol. It is nearly insoluble in diluted acids, and is 
one of the chief forms in which lead is precipitated from its solutions in 
analytical operations. The minerals lanarkite and leadliillite are com- 
pounds of sulphate and carbonate of lead. The chromates of lead have 
been already noticed. 

Lead, phosphate, Pb 3 (P0 4 ) 2 , is occasionally associated with the car- 
bonate in the ores of lead. 

278. Lead chloride (PbCl 2 ) forms the mineral termed horn lead. It 
is one of the few chlorides which are not readly soluble in water, and is 
precipitated when hydrochloric acid or a soluble chloride is added to a 
solution of lead. Boiling water dissolves about g 1 ^ of its weight of lead 
chloride, and deposits it in beautiful shining white needles on cooling. It 
fuses easily, and is converted into vapour at a high temperature. The 
specific gravity of this vapour at 1070° C. is 9*64 (theory requires 9 # 62). 

The lead oxychloride (PbCl 2 .PbO) is formed when lead chloride is 



THALLIUM. 377 

heated in air. It is sometimes employed as a substitute for white lead in 
painting, being prepared for this purpose by decomposing finely-powdered 
galena with concentrated hydrochloric acid (PbS + 2HC1 = PbCl + H 2 S), 
washing the resulting lead chloride with cold water, dissolving it in hot 
water, and adding lime-water, which precipitates the oxychloride; 2PbCl 9 
+ CaO = PbCl 2 . PbO + CaCl 2 . 

Turner s yellow (Paris yellow, patent yellow, mineral yellow) is another 
oxychloride of lead (PbCT.,.7PbO), prepared by heating a mixture of lith- 
arge and sal-ammoniac. It has a fine golden yellow colour, is easily fused, 
and crystallises in octahedra on cooling. The mineral mendipite is an 
oxychloride of lead (PbCi. 7 .2PbO) which occurs in colourless prismatic 
crystals. 

Lead clilorooromicle (PbBrCl) has been found in crystals resembling lead 
chloride among the furnace-products in smelting lead carbonate ore. 

Lead iodide (Pbl 9 ) is obtained as a bright yellow precipitate on mix- 
ing solutions of nitrate or acetate of lead and potassium iodide. If it 
be allowed to settle, the liquid poured off, and the precipitate dissolved 
in boiling water (with one or two drops of hydrochloric acid), it forms a 
colourless solution, depositing golden scales as it cools. 

279. Sulphides of lead. — The subsulphide (Pb 9 S) has been mentioned 
as produced in smelting galena. Sulphide of lead, or galena, has been 
described among the ores of lead. It is always obtained as a black 
precipitate when hydrosulphuric acid or a soluble sulphide acts upon 
a solution containing lead, even in minute proportion. 

A persulphide of lead, the composition of which has not been ascer- 
tained, is formed as a red precipitate when a solution of lead is mixed 
with a solution of an alkaline sulphide saturated with sulphur (or with 
solution of ammonium sulphide which has been kept till it has acquired a 
red colour). It is probably PbS 5 . 

Lead chlorosuljjhide (3PbS.2PbCl 2 ) is obtained as a bright red pre- 
cipitate when hydrosulphuric acid is added in small quantity to a solution 
of lead chloride in hydrochloric acid. 

Lead selenide (PbSe) occurs associated with the sulphide in some lead 
ores ; it much resembles galena, and has the same crystalline form. 

280. Thallium (Tl = 201 parts by weight).— The discovery of this metal in 1861 
was one of the first results of the application of the new method of testing by obser- 
vation of coloured lines in the spectrum of a flame, described at p. 272. Crookes was 
examining the spectrum obtained by holding in the flame of a Bunsen burner the 
deposit formed in the flues of a sulphuric acid chamber, in which pyrites was 
employed as the source of sulphur. A green line made its appearance in the spectrum, 
which a less acute and practised observer might have mistaken for one of the lines 
caused by barium (see fig. 235), with which it nearly coincides in position ; but the 
line was much brighter than that produced by barium, and on instituting a searching 
analysis of the deposit, a metal was obtained which did not agree in properties with 
any hitherto described, and was named thallium, from QaXXos, a young shoot, in 
allusion to the vernal green colour of its spectrum line. It has since been detected 
in several mineral waters ; but the pyrites obtained from Spain and Belgium appear 
to be its best source. From the flue-dust of the sulphuric acid chambers, the metal 
is extracted by a simple process, but large quantities must be operated on to obtain 
any considerable amount. The deposit is treated with boiling water, and the solution 
mixed with much strong hydrochloric acid, which precipitates the thallium as 
thallous chloride (T1U1) ; this is converted into acid thallous sulphate (T1HS0 4 ) by 
treatment with sulphuric acid, and this salt having been purified by recrystallisation, 
is decomposed by zinc, which precipitates metallic thallium in a spongy form, fusible 
into a compact mass in an atmosphere of coal gas. 



378 SILVER. 

Iii external characters thallium is very similar to lead ; but it tarnishes much 
more rapidly when exposed to air, and the streak which it makes on paper soon 
becomes yellowish, being converted into thallous oxide, T1 2 0. If a tarnished piece of 
the metal be allowed to touch the tongne, a strongly alkaline taste is perceived, for 
the thallous oxide (T1. 2 0) is very soluble in water, so that the tarnished metal becomes 
bright when immersed in water. If granulated thallium be exposed to moist air in 
a warm place, it absorbs oxygen and carbonic acid gas. On boiling with water and 
filtering, the alkaline solution deposits white needles of thallous carbonate (T1 2 C0 3 ), 
and afterwards yellow needles of thallous hydrate (TIOH). The ready solubility of 
the oxide seemed to require thallium to be classed among the alkali-metals, a view 
which was encouraged by the circumstance that its specific heat proved it to be 
monatomic like potassium and sodiurm But thallium appears to be more nearly 
related to another monatomic metal, silver, by the sparing solubility of its chloride 
and the insolubility of its sulphide. The circumstance that it maybe kept unaltered 
in water and may be precipitated from its salts by zinc, at once removes it from the 
group of alkali-metals. The ready solubility of its oxide in water is only an exaggera- 
tion of the behaviour of the oxides of lead and silver, both of which dissolve slightly 
in water, yielding alkaline solutions. Moreover, its hydrate is far less stable than 
those of potassium and sodium, for it becomes T1 2 when dried in vacuo over oil of 
vitriol. Diluted sulphuric acid acts upon thallium as upon zinc, evolving hydrogen. 
It is not much affected by diluted nitric acid in the cold ; even on heating, the action 
is slow unless the acid is very weak. On cooling, the solution becomes filled with 
needles of thallous nitrate. Thallium burns in oxygen with a beautiful green flame, 
and the thallous chlorate has been recommended for the manufacture of green fires in 
place of barium chlorate (see page 166). 

Thallous sulphate, T1 2 S0 4 , is obtained by dissolving thallium in sulphuric acid 
and evaporating ; the acid sulphate, T1HS0 4 , first produced, being decomposed by 
further heating. T1 2 S0 4 is isomorphous with K S0 4 , and it forms thallous alum, 
TlAl(S0 4 ). 2 .12Aq. crystallising like potash-alum. 

Thallous chloride, T1C1, resembles lead chloride, being precipitated by adding HC1 
to a solution of a thallous salt, and being dissolved by boiling water from which it 
crystallises on cooling. 

Thallous iodide, Til, is obtained as a yellow precipitate on adding potassium iodide 
to a thallous salt ; when dried and heated, it fuses to a red liquid which remains red 
after solidifying, and changes, after a time, to yellow. When spread on paper, the 
yellow iodide becomes red when heated, and remains red on cooling, but becomes 
yellow when rubbed with a hard body. 

Thallous sulphide, T1. 2 S, is deposited as a brownish-black precipitate, on adding 
ammonium sulphide to a thallous salt. 

Thallic oxide, T1 2 3 , is obtained by adding sodium hypochlorite to thallous chloride 
mixed with excess of sodium carbonate. It is a dark red substance, which evolves 
oxygen and leaves thallous oxide when heated. It is also a basic oxide, its sulphate' 
having the composition Tb>(S0 4 ) 3 .H 2 0.6Aq. 

Thallic chloride, T1C1 3 , is formed by heating thallium in excess of chlorine ; it is 
soluble and crystallisable. 

Salts of thallium, like those of lead, are poisonous. 



SILVEE. 

Ag = 108 parts by weight. 

281. In silver, we meet with the first metal hitherto considered which 
is not capable of undergoing oxidation in the air, and this, in conjunction 
with its beautiful appearance, occasions its manifold ornamental uses, 
which are much favoured also by the great malleability and ductility 
of this metal (in which it ranks only second to gold), for the former 
property enables it to be rolled out into thin plates or leaves, so that a 
small quantity of silver suffices to cover a large surface, whilst its ductility 
permits the wire-drawer to produce that extremely thin silver wire which 
is employed in the manufacture of silver lace. 

Silver, although pretty widely diffused, is found in comparatively small 



LIQUATION — AMALGAMATION. 



379 



quantity, and hence it bears a high value, which adapts it for a medium 
of currency. 

As might be expected from its want of direct attraction for oxygen, 
silver is found frequently in the metallic or native state, crystallised in 
cubes or octahedra, which are sometimes aggregated together, as in the 
silver-mines of Potosi, into arborescent or dendritic forms.* Silver is 
more frequently met with, however, in combination with sulphur, forming 
the sulphide of silver (Ag 2 S), which is generally associated with large 
quantities of the sulphides of lead, antimony, and iron. The largest sup- 
plies of silver are obtained from the Mexican and Peruvian mines, but the 
quantity furnished by Saxony and Hungary is by no means insignificant. 
The process by which silver is extracted from galena has been already 
described under the history of lead. 

The ores of copper (particularly the grey copper ore) often contain so 
much silver as to be worth working for that metal, in which case they 
are smelted in the usual way, when the copper obtained is found to con- 
tain the whole of the silver present 
in the ore. The silver is separated 
from the copper by taking advantage 
of the facility with which the former 
metal is dissolved by melted lead. 
The process of liquation, as it is 
termed, consists in fusing the argenti- 
ferous copper with about thrice, its 
weight of lead, and casting the alloy 
thus obtained into cakes or discs, 
which are afterwards gradually heated 
upon a hearth (fig. 269), so contrived 
that the lead, which melts much more 
easily than the copper, may flow off 

in the liquid state, carrying with it, in the form of an alloy, the silver 
which was associated with the copper, leaving this last metal in 
porous masses, having the form of the original discs, upon the hearth. 
The lead and silver are separated by the process of cupellation (page 
370). 

When the extraction of the silver is the main object with which a 
particular ore is treated, the process of amalgamation is adopted, in which 
the silver is dissolved out by means of mercury. At Freiberg, the silver 
is extracted by this method from an ore which contains silver sulphide 
together with much iron pyrites and other metallic sulphides. The ore 
is mixed with a small proportion of common salt, and roasted in a rever- 
beratory furnace, when the silver sulphide is converted into silver chloride. 
It is then ground to a very fine powder, which is agitated, in revolving 
casks, with water and metallic iron, when the latter appropriates the 
chlorine and reduces the silver to the metallic state. A quantity of 
mercury is then introduced into the casks, and the revolution continued 
for several hours; the mercury dissolves the silver, copper, and lead, and 
is run out of the barrels into stout linen strainers, winch allow the excess 
of fluid mercury to pass through, but retain the soft solid amalgam con- 
taining the silver. In order to recover the silver, this amalgam is placed 

* Flight found 23 per cent, of mercury in a specimen of native silver from Kongsberg. 
Other samples also proved to be amalgams. 




Fig. 269.— Liquation hearth. 



380 



SILVER-PLATING. 




Fig. 270. 



in iron trays arranged one above the other (fig. 270), and covered with 
an iron bell-shaped receiver standing over water. By heaping burning 
fuel round the upper part of this dome, its temperature is raised sufficiently 

to convert the mercury into vapour, which 
condenses again in the water, leaving the silver, 
together with the copper and lead, upon the 
iron trays. Finally, the silver is refined by 
fusing it with an additional quantity of lead 
and subjecting the alloy to cupellation (page 
370), when the fused oxide of lead which is 
formed carries with it the copper, also in the 
form of oxide, leaving the silver in a state of 
purity. 

Various methods have been devised to 
supersede the amalgamation process. For 
example, the ores have been roasted with 
common salt to convert the silver into chloride, 
which is dissolved out of the mass by means 
of a strong solution of common salt, from 
which the silver is afterwards precipitated in the metallic state by copper. 
Sodium hyposulphite has also been employed to dissolve out the silver 
chloride, and the solution precipitated by sodium sulphide, the resulting 
silver sulphide being roasted to remove the sulphur and leave metallic 
silver. 

Although silver is capable of resisting the oxidising action of the atmo- 
sphere, it is liable to considerable loss by wear and tear in consequence 
of its softness, and is therefore always hardened, for useful purposes, by 
the addition of a small proportion of copper. The standard silver em- 
ployed for coinage and for most articles of silver plate in this country, 
contains, in 1000 parts, 925 of silver and 75 of copper, whilst that used 
in France contains 900 of silver and 100 of copper. 

Standard silver, for coining and other purposes, is whitened by being 
heated in air and immersed in diluted sulphuric acid, which dissolves out 
the oxide of copper, leaving a superficial film of nearly pure silver. Dead 
or frosted, silver is produced in this manner. Oxidised silver is covered 
with a thin film of sulphide by immersion in a solution obtained by 
boiling sulphur with potash. 

The solder employed in working silver consists of 5 parts of silver, 2 
of zinc, and 6 of brass. 

Plated articles are manufactured from copper or one of its alloys, 
which has been united, by rolling, with a thin plate of silver, the adhesion 
of the latter being promoted by first washing the surface of the copper 
with a solution of nitrate of silver, when a film of this metal is deposited 
upon its surface, the copper taking the place of the silver in the solution. 
Electro --plating consists in covering the surface of baser metals with a 
coating of silver, by connecting them with the negative (or zinc) pole of 
the galvanic battery, and immersing them in a solution made by dissolving 
silver cyanide in potassium cyanide;* the current gradually decomposes 
the silver cyanide, and this metal is of course (see page 9) deposited upon 
the object connected with the negative pole, whilst the cyanogen liberated 

* A solution of potassium cyanide in 10 parts of water, with 50 grains of silver chloride 
dissolved in each pint of the liquid, will answer the purpose. 



PROPERTIES OF SILVER. 381 

at the positive (copper or platinum) pole is allowed to act upon a silver 
plate with which this pole is connected, so that the silvering solution is 
always maintained at the same strength, the quantity of silver dissolved 
at this pole being precisely equal to that deposited at the opposite pole. 

Brass and copper are sometimes silvered by rubbing them with a mix- 
ture of 10 parts of silver chloride, with 1 of corrosive sublimate (mercuric 
chloride) and 100 of bitartrate of potash. The silver and mercury are 
both reduced to the metallic state by the baser metal, and an amalgam 
of silver is formed, which readily coats the surface. The acidity of the 
bitartrate of potash promotes the reduction. The surface to be silvered 
should always be cleansed from oxide by momentary immersion in nitric 
acid, and washed with water. For dry silvering, an amalgam of silver 
and mercury is applied to the clean surface, and the mercury is after- 
wards expelled by heat. 

Silvering upon glass is effected by means of certain organic substances 
which are capable of precipitating metallic silver from its solutions. 
Looking-glasses have been made by pouring upon the surface of plates of 
glass a solution containing silver tartrate and ammonium tartrate. On 
heating the glass plates to a certain temperature, the tartrate is reduced, 
and the metallic silver is deposited in a closely adhering film. Glass globes 
and vases are silvered internally by a process which is exactly similar 
in principle. The coating is rendered more adherent by sprinkling it 
with a weak solution of potassio-mercuric cyanide, which amalgamates the 
silver. 

Small surfaces of glass for optical purposes may be silvered in the following manner : — 
Dissolve one gramme of silver nitrate in 20 cubic centimetres of distilled water, and 
add weak ammonia carefully until the precipitate is almost entirely dissolved. Filter 
the solution, and make it up to 100 cubic centimetres' with distilled water. Then 
dissolve 2 grammes of silver nitrate in a little distilled water, and add it to a litre of 
boiling distilled water. Add 1 '66 gramme of Rochelle salt (tartrate of potassium and 
sodium), and boil till the precipitated silver tartrate becomes grey ; filter while hot. 

Clean the glass to be silvered very thoroughly with nitric acid, distilled water, 
potash, distilled water, alcohol, distilled water ; place it in a clean glass or porcelain 
vessel, with the side to be silvered uppermost. Mix equal measures of the two silver 
solutions (cold), and pour the mixture in so as to cover the glass, which will be 
silvered in about an hour. After washing, it may be allowed to dr}% and varnished 
{Instruction in Physics in the Laboratory at South Kensington). 

Pure silver is easily obtained from standard silver by dissolving it in 
nitric acid, with the aid of heat, diluting the solution with water, adding 
solution of common salt as long as it produces any fresh precipitate of 
silver chloride, washing the precipitate by decantation as long as the- 
washings give a blue tinge with ammonia, and fusing the dried precipitate 
with half its weight of dried carbonate of soda in a brisk fire, when a 
button of silver will be found on breaking the crucible — 

2AgCl + Na 2 C0 3 = Ag 2 + 2NaCl + O + C0 2 . 
282. Properties of silver. — The brilliant whiteness of silver distin- 
guishes it from all other metals. It is lighter than lead, its specific 
gravity being 10*53 ; harder than gold, but not so hard as copper; more 
malleable and ductile than any other metal except gold, which it sur- 
passes in tenacity. It fuses at a somewhat lower temperature than gold or 
copper (about 1900° F., 1037° G), and is the best conductor of heat and 
electricity. It is not oxidised by dry or moist air, either at the ordinary 
or at high temperatures, but is oxidised by ozone, and tarnished by air 



382 OXIDES OF SILVER. 

containing sulphuretted hydrogen, from the production of silver sulphide, 
which is easily removed hy solution of potassium cyanide. It is unaffected 
by dilute acids, with the exception of nitric; but hot concentrated sul- 
phuric acid converts it into silver sulphate, and when boiled with strong 
hydrochloric acid, it dissolves to a slight extent in the form of silver 
chloride, which is precipitated on adding water. The potassium and 
sodium hydrates do not act on silver to the same extent as on platinum 
when fused with it ; hence silver basins and crucibles are much used in 
the laboratory. 

283. Oxides of silver. — There are three compounds of silver with 
oxygen : the suboxide Ag 4 ; the oxide Ag 2 ; and the peroxide, probably 
Ag 2 2 , which is not known in the pure state, The oxide alone has any 
practical interest, as being the base of the salts of silver. 

Silver oxide (Ag 2 0) is obtained as a brown precipitate when solution 
of silver nitrate is decomposed by potash. It is a powerful base, slightly 
soluble in water, to which it imparts a weak alkaline reaction. A 
moderate heat decomposes it into its elements. When moist freshly- 
precipitated silver oxide is covered with a strong solution of ammonia, 
and allowed to stand for some hours, it becomes black, and acquires 
dangerously explosive properties. The composition of this fulminating 
silver is not accurately known, but it is supposed to be a silver nitride 
NAg 3 , corresponding in composition to ammonia. 

Silver nitrate (Ag\N~0 3 ), or lunar caustic (silver being distinguished 
as luna by the alchemists), is procured by dissolving silver in nitric acid, 
with the aid of a gentle heat, evaporating the solution to dryness, and 
heating the residue till it fuses, in order to expel the excess of acid. For 
use in surgery, the fused nitrate is poured into cylindrical moulds, so as 
to cast it into thin sticks ; but for chemical purposes it is dissolved in 
water and crystallised, when it forms colourless square tables. The action 
of nitrate of silver as a caustic depends upon the facility with which it 
parts with oxygen, the silver being reduced to the metallic state, and the 
oxygen combining with the elements of the organic matter. This effect 
is very much promoted by exposure to sunlight, or diffused daylight. 
Pure silver nitrate is not changed by exposure to light, but if organic 
matter be present, a black deposit, containing finely-divided silver, is pro- 
duced. Thus, the solution of silver nitrate stains the fingers black 
when exposed to light, but the stain may be removed by potassium 
cyanide. If solution of silver nitrate be dropped upon paper, and exposed 
to light, black stains will be produced, and the paper corroded. Silver 
nitrate is a frequent constituent of marking inks, since the deposit of 
metallic silver formed on exposure to light is not removable by washing: 
The linen is sometimes mordanted by applying a solution of sodium 
carbonate before the marking ink, when the insoluble silver carbonate is 
precipitated in the fibre, and is more easily blackened than the nitrate, 
especially if a hot iron is applied. Marking inks without preparation are 
made with silver nitrate containing an excess of ammonia, which appro- 
priates the nitric acid, and hastens the blackening on exposure to light 
or heat. Hair dyes often ' contain silver nitrate. The important use of 
this salt in photography has been noticed already (page 212). 

In order to prepare silver nitrate from standard silver (containing copper), the 
metal is dissolved in moderately strong nitric acid, and the solution evaporated to 



CHLORIDE OF SILVER. 383 

dryness in a porcelain dish, when a blue residue containing the nitrates of silver and 
copper is obtained. The dish is now moderately heated until the residue has fused, 
and become uniformly black, the blue copper nitrate being decomposed and leaving 
black copper oxide, at a temperature which is insufficient to decompose the silver 
nitrate. To ascertain when all the copper nitrate. is decomposed, a small sample is 
removed on the end of a glass rod, dissolved in water, filtered, and tested with 
ammonia, which will produce a blue colour if any copper nitrate is left.. The residue 
is treated with hot water, the solution filtered from the copper oxide, and evaporated 
to crystallisation. 

284. Silver chloride (AgCl) is an important compound, as being the 
form into which silver is commonly converted in extracting it from its 
ores, and in separating it from other metals. It separates as a white 
curdy precipitate, when solution of hydrochloric acid or a chloride is 
mixed with a solution containing silver. The precipitate is brilliantly 
white at first, but soon becomes violet, and eventually black, if exposed 
to daylight, or more rapidly in sunlight, the chloride of silver being re- 
duced to subchloride (Ag 2 Cl), with separation of chlorine (see page 213). 
The blackening takes place more rapidly in the presence of an excess of 
silver nitrate or of organic matter, upon which the liberated chlorine is 
capable of acting. The silver chloride formed by suspending silver leaf 
in a bottle of chlorine gas, is not blackened by light. If the white silver 
chloride be dried in the dark, and heated in a crucible, it fuses at about 
500° F., to a brownish liquid, which solidifies, on cooling, to a transparent, 
nearly colourless mass, much resembling horn in external characters 
{horn silver) ; a strong heat converts it into vapour, but does not decom- 
pose it. If fused silver chloride be covered with hydrochloric acid, and 
a piece of zinc placed upon it, it will be found entirely reduced, after a 
few hours, to a cake of metallic silver ; the first portion of silver having 
been reduced in contact with the zinc, and the remainder by the galvanic 
action set up by the contact of the two metals beneath the liquid. 
Ammonia readily dissolves silver chloride, and the solution deposits 
colourless crystals of the chloride when evaporated. If the ammonia be 
very strong, the solution deposits a crystalline compound of silver chloride 
with ammonia. The absorption of ammoniacal gas by silver chloride has 
been noticed at page 127, and the photographic application of the chloride 
at page 213. 

Recovery of silver from old photographic baths. — One of the simplest methods of 
effecting this consists in mixing the liquid with solution of common salt as long as 
it causes a fresh precipitate of silver chloride, which is allowed to subside, washed 
once or twice by decantation, mixed with a little sulphuric acid, a lump of zinc 
(spelter) placed in it, and left for a day or two to reduce the silver to the metallic 
state. The zinc is then taken out, and the metallic silver well washed by decanta- 
tion, first with dilute sulphuric acid, to remove zinc, and afterwards with water, till 
the washings are quite tasteless. It may either be reconverted into nitrate by dissolving 
in nitric acid (p. 382), or fused in an earthen crucible with a little borax. 

From the fixing solutions containing sodium hyposulphite, the silver cannot be 
precipitated by salt, because the silver chloride is soluble in the hyposulphite. A 
piece of sheet copper left in this for a day or two will precipitate the silver at once in 
the metallic state. 

Subchloride of silver ( Ag^Cl) has been been obtained by the action of ferric chloride 
upon metallic silver (Ag4 + Fe 2 Cl 6 = 2Ag. 2 Cl + 2FeCL>). It is black, and insoluble 
in nitric acid. Ammonia decomposes it, dissolving out silver chloride, and leaving 
metallic silver. 

Another subchloride of silver, Ag 4 Cl 3 , has been obtained as a black powder by the 
action of hydrochloric acid upon the argentous citrate prepared by reducing argentic 
citrate with hydrogen. 



384 MERCURY. 

Silver bromide (AgBr) is a rare Chilian mineral. Associated with 
silver chloride, it forms the mineral embolite. It much resembles the 
chloride, but is somewhat less easily dissolved by ammonia. 

Silver iodide (Agl) is also found in the mineral kingdom. It is 
worthy of remark that silver decomposes hydriodic acid much more easily 
than hydrochloric acid, forming silver iodide, and evolving hydrogen. 
The silver iodide dissolves in hot hydriodic acid, and is deposited in 
crystals on cooling. By adding silver nitrate to potassium iodide the 
silver iodide is obtained as a yellow precipitate which, unlike the chloride, 
does not dissolve in ammonia. Silver iodide dissolves in a boiling 
saturated solution of silver nitrate, and the solution, on cooling, deposits 
crystals having the composition AgI.AgN0 3 , which are far more sensitive 
to the action of light than silver iodide itself, a circumstance which is 
taken advantage of by photographers. The crystals are decomposed by 
water, with separation of silver iodide. 

Silver sulphide (Ag 2 S) is found as silver glance, which may be regarded 
as the chief ore of silver ; it has a metallic lustre, and is sometimes found 
in cubical or octahedral crystals. The minerals known as rosiclers or red 
silver ores contain sulphide of silver combined with the sulphides of 
arsenic and antimony. The black precipitate obtained by the action of 
hydrosulphuric acid upon a solution of silver is silver sulphide. It may 
also be formed by heating silver with sulphur in a covered crucible. 
Silver sulphide is remarkable for being soft and malleable, so that medals 
may even be struck from it. It is not dissolved by diluted sulphuric or 
hydrochloric acid, but nitric acid readily dissolves it. Metallic silver 
dissolves silver sulphide when fused with it, and becomes brittle even 
when containing only 1 per cent, of the sulphide. 



MERCURY. 

Hg" = 200 parts by weight.* 

285. Mercury (quicksilver) is the only metal which is liquid at the 
ordinary temperature, and since it requires a temperature of 39° below' 
zero E. to solidify it, this metal is particularly adapted for the construc- 
tion of thermometers and barometers. Its high boiling-point (662° F.) 
also recommends it for the former purpose, as its high specific gravity 
(13 '54) for the latter, a column of about 30 inches in height being- 
able to counterpoise a column of atmospheric air having the same 
sectional area, and a height equal to that of the atmosphere above the. 
level of the sea. The symbol for mercury (Hg) is derived from the Latin 
name for this element, hydrargyrum (vSwp, water, referring to its fluidity, 
apyvpos, silver). 

Mercury is not met with in this country, but is obtained from Idria 
(Austria), Almaden (Spain), China, and New Almaden (California). It 
occurs in these mines partly in the metallic state, diffused in minute 
globules or collected in cavities, but chiefly in the state of cinnabar, which 
is mercuric sulphide (HgS). 

The metal is extracted from the sulphide at Idria by roasting the ore 

* The vapour of mercury is only 100 times as heavy as hydrogen, which would indicate 
100 as the atomic weight of mercury, hut the specific heat of mercury when multiplied hy 
100 would give an atomic heat only half that of most other metals. 



MERCURY. 



385 



in a kiln (fig. 271), which is connected with an extensive series of - con- 
densing chambers built of brickwork. The sulphur is converted, by the 
air in the kiln, into sulphurous acid gas, whilst the mercury passes off in 
vapour and condenses in the chambers. 





Fig. 



Fig. 271. — Extraction of mercury at Idria. 

At Almaden, the extraction is conducted upon the same principle, but 
the condensation of the mercury is effected in earthen receivers (called 
uludels) opening into each other, and delivering the mercury into, a gutter 
which conveys it to the receptacles. 

The cinnabar is placed upon the arch (A, fig. 272) of brickwork, in 
which there are several openings for the passage of the flame of the wood 
fire kindled at B ; this flame 
ignites the sulphide of mercury, 
which burns in the air passing 
up from below, forming sul- 
phurous acid gas and vapour of 
mercury (HgS + 2 = Hg -f 
S0 2 ), which escape through the 
flue (F) into the aludels (C), 
where the chief part of the 
mercury condenses and runs 
down into the gutter (G). The 
sulphurous acid gas escapes 

through the flue (H), and any mercury which may have escaped condensa- 
tion is collected in the trough (D), the gas finally passing out through 
the chimney (E), which provides for the requisite draught. 

In the Palatinate, the cinnabar is distilled in cast-iron retorts with 
lime, when the sulphur is left in the residue as calcium sulphide and 
sulphate, whilst the mercury distils over — 

4HgS -f 4CaO = 3CaS + CaS0 4 + Hg 4 . 

The mercury found in commerce is never perfectly pure, as may be shown by 
scattering a little upon a clean glass plate, when it tails or leaves a track upon the 
glass, which is not the case with pure mercury. Its chief impurity is lead, which 
may be removed by exposing it in a thin layer to the action of nitric acid diluted 
with two measures of water, which should cover its surface, and be allowed to remain 
in contact with it for a day or two, with occasional stirring. The lead is far more 
easily oxidised and dissolved than the mercury, though a little of this also passes 
into solution. The mercury is afterwards well washed with water and dried, first with 
blotting-paper, and then by a gentle heat. Mercury is easily freed from mechanical 
impurities by filtering it through a cone of paper, round the apex of which a few pin- 
holes have been made. Zinc, tin, and bismuth are sometimes present in the mercury 
of commerce. 

2 b 



386 USES OF MERCURY. 

286. Although mercury in its ordinary condition is not oxidised by air 
at the common temperature, it appears to undergo a partial oxidation 
when reduced to a fine state of division, as in those medicinal prepara- 
tions of the metal which are made by triturating it with various sub- 
stances which have no chemical action upon it, until globules of the metal 
are no longer visible. Blue pill and grey powder, or hydrargyrum cum 
cretd, afford examples of this, and probably owe much of their medicinal 
activity to the presence of one of the oxides of mercury. 

287. Uses of mercury.- — One of the chief uses to which mercury is 
devoted is the silvering of looking-glasses, which is effected by means of 
an amalgam of tin in the following manner: a sheet of tin-foil of the 
same size as the glass to be silvered is laid perfectly level upon a table, 
and rubbed over with metallic mercury, a thin layer of which is after- 
wards poured upon it. The glass is then carefully slid on to the table, 
so that its edge may carry before it part of the superfluous mercury with 
the impurities upon its surface ; heavy weights are laid upon the glass so 
as to squeeze out the excess of mercury, and in a few days the combina- 
tion of tin and mercury is found to have adhered firmly to the glass ; this 
coating usually contains about 1 part of mercury and 4 parts of tin. In 
this and all other arts in which mercury is used (such as barometer-mak- 
ing) much suffering is experienced by the operatives, from the poisonous 
action of the mercury. 

The readiness with which mercury unites with most other metals to 
form amalgams is one of its most striking properties, and is turned to 
account for the extraction of silver and gold from their ores. The attrac- 
tion of the latter metal for mercury is seen in the readiness with which 
it becomes coated with a silvery layer of mercury, whenever it is brought 
in contact with that metal, and if a piece of gold leaf be suspended 
at a little distance above the surface of mercury, it will be found, after 
a time, silvered by the vapour of the metal which rises slowly even at 
the ordinary temperature. From the surface of rings which have been 
accidentally whitened by mercury, it may be removed by a moderate 
heat, or by warm dilute nitric acid, but the gold will afterwards require, 
burnishing. 

Zinc plates are amalgamated, as it termed, for use in the galvanic 
battery, by rubbing the liquid metal over them under the surface of dilute 
sulphuric acid, which removes the coating of oxide from the surface of 
1 lie zinc. The amalgam of zinc is not acted on by the diluted sulphuric 
acid used in the battery (see page 8) until the circuit is completed, so that 
no zinc is wasted when the battery is not in use. An amalgam of 6 parts 
of mercury with 1 part of zinc and 1 of tin is used to promote the action 
of electrical machines. 

The addition of a little amalgam of sodium to metallic mercury gives 
it the power of adhering much more readily to other metals, even to iron. 
Such an addition has been recommended in all cases where metallic sur- 
faces have to be amalgamated, and especially in the extraction of silver 
and gold from their ores by means of mercury. 

Iron and platinum are the only metals in ordinary use which can be 
employed in contact with mercury without being corroded by it. Mer- 
cury, however, adheres to platinum. 

The following definite compounds of mercury with other metals have been ob« 



OXIDES OF MERCURY, 387 

tained by combining them with excess of mercury, and squeezing out the fluid metal 
by hydraulic pressure, amounting to 60 tons upon the inch : — 



Amalgam of lead, 


PboHg 


Amalgam of zinc, 


Zn 2 Hg 


,, silver. 


AgHg 


,, copper, 


CuHg 


,, iron, 


FeHg* 


,, platinum, 


PtHg 2 



The amalgam of silver (AgHg) has been found in nature, in dodecahedral crystals. 

A very beautiful crystallisation of the amalgam of silver {Arbor Dianas) may be 
obtained in long prisms having the composition AgoHg 3 , by dissolving 400 grains of 
silver nitrate in 40 measured ounces of water, adding 160 minims of concentrated 
nitric acid, and 1840 grains of mercury ; in the course of a day or two crystals of 2 or 
3 inches in length will be deposited. 

288. Oxides of mercury. — Two oxides of mercury are known, the sub- 
oxide Hg 2 0, and the oxide HgO : both combine with acids to form salts. 

Suboxide of mercury, black oxide or mercurous oxide, Hg.,0, is obtained 
by decomposing calomel with solution of potash, and washing with water 
(Hg 2 Cl 2 + 2KHO = Hg 2 + 2KC1 + H 2 0). It is very easily decomposed, 
by exposure to light or to a gentle heat, into mercuric oxide and metallic 
mercury. 

Red oxide of mercury or mercuric oxide (HgO) is formed upon the 
surface of mercury, when heated for some time to its boiling-point in con- 
tact with air. The oxide is black while hot, but becomes red on cooling. 
It is used under the name of red precipitate, in ointments, and is prepared 
for this purpose by dissolving mercury in nitric acid, evaporating the 
solution to dryness, and gently calcining the mercuric nitrate, Hg(X0 3 ) 2 . 
until the nitric acid is expelled. The name nitric oxide of mercury refers 
to this process. It is thus obtained, after cooling, as a brilliant red crys- 
talline powder, which becomes nearly black when heated, and is resolved 
into its elements at a red heat. It dissolves slightly in water, and the 
solution has a very feeble alkaline reaction. A bright yellow modification 
of the oxide is precipitated when a solution of corrosive sublimate is 
decomposed by potash (HgCl 2 + 2KHO = HgO + 2KC1 + H 2 0) : the yellow 
variety is chemically more active than the red. 

"When mercuric oxide is acted on by strong ammonia, it becomes converted into a 
yellowish- white powder which possesses the properties of a strong base, absorbing 
carbonic acid eagerly from the air, and combining readily with other acids. It is 
easily decomposed by exposure to light, and, if rubbed in a mortar when dry, is 
decomposed with slight detonations, a property in which it feebly resembles fulmin- 
ating silver (p. 382). The composition of this substance is represented by the 
formula 4Hg0.2XH 3 .2HoO, and it is sometimes called ammoniatcd mercuric oxide. 
"When exposed in vacuo over oil of vitriol, it loses 2HoO, becoming 4Hg0.2XH 3 , but 
if heated to about 260° F., it becomes brown ;t it now contains Hg 4 3 XoH 4 , and may 
be regarded as a compound of mercuric oxide with two molecules of ammonia in which 
two atoms of hydrogen are displaced by mercury (XoH 4 Hg' / ,3HgO). 

This substance is sometimes called mcrcuramine ; it forms salts with the acids. 

By passing ammonia gas over the yellow oxide of mercury as long as it is absorbed, 
and heating the compound to about 260 3 F. in a current of ammonia as long as any 
water is evolved, a brown explosive powder is obtained which is believed to be a 
nitride of mercury, XoHg 3 ", representing a double molecule of ammonia in which the 
hydrogen has been displaced by mercury. It yields salts of ammonium when decom- 
posed by acids. 

289. The salts formed by the oxides of mercury with the oxygen-acids are not of 
great practical importance. Protonitrate of mercury or mercurous nitrate is obtained 

* Hg 3 Fe 2 has been obtained by the action of finely-divided iron on sodium-amalgam in 
Tjresence of water. 

+ It has been stated that by heating it for some time in £ current of dry ammonia, the 
whole of the oxygen may be expelled as water, leaving the oxide of mercurammonium 
(NHgo'^oO, which is very explosive, and combines with water to form a hydrate which 
produces salts with the acids. 



388 CHLOKIDES OF MERCURY. 

when mercury is dissolved in nitric acid diluted with 5 volumes of water ; it may 
be procured in crystals having the composition Hg. 2 (N0 3 ) 2 ,2Aq. The prismatic 
crystals which are sometimes sold as protonitrate of mercury consist of a basic nitrate, 
3Hg 2 (N0 3 ). 2 ,Hg 2 O.H. 2 0, prepared by acting with diluted nitric acid upon mercury 
in excess. When this salt is powdered in a mortar with a little common salt, it 
becomes black from the separation of mercurous oxide — 

3Hg. 2 (N0 3 )o,Hg. 2 O.H 2 + 6NaCl = 3Hg 2 Cl 2 + 6NaN0 3 + Hg 2 + H 2 ; 
but the normal nitrate is not blackened (Hg. 2 (N0 3 ) 2 + 2NaCl = Hg 2 Cl 2 + 2NaN0 3 ). 
These nitrates cannot be dissolved in water without partial decomposition and pre- 
cipitation of yellow basic nitrates. 

Nitrate of mercury or mercuric nitrate is formed when mercury is dissolved with an 
excess of strong nitric acid, and the solution boiled. It is better to prepare it by 
saturating strong nitric acid, diluted with an equal measure of water, with mercuric 
oxide. It maybe obtained in crystals of the formula 2Hg(N0 3 ) 2 .Aq. "Water decom- 
poses it, precipitating a yellow basic nitrate, which leaves mercuric oxide when long 
washed with water. 

Mercurous sulphate (Hg. 2 S0 4 ) is precipitated as a white crystalline powder when 
dilute sulphuric acid is added to a solution of mercurous nitrate. 

Mercuric sulphate (HgS0 4 ) is obtained by heating 2 parts by weight of mercury 
with 3 parts of oil of vitriol, and evaporating to dryness. Mercurous sulphate is first 
produced, and is oxidised by the excess of sulphuric acid. It forms a white ciystalline 
powder, which is decomposed by water into a soluble acid sulphate, and an insoluble 
yellow basic sulphate of mercmy, HgS0 4 ,2HgO, known as turbith or turpeth mineral, 
said to have been so named from its resembling in its medicinal effects the root of the 
Convolvulus turpethum. 

290. Chlorides of mercury. — The chlorides are the most important 
of the compounds of mercury, one chloride being calomel (HgCl or Hg 2 Cl 2 ) 
and the other corrosive sublimate (HgCl 2 ). Vapour of mercury burns in 
chlorine gas, corrosive sublimate being produced.* 

Corrosive sublimate, chloride of mercury, bichloride or perchloride of 
mercury, or mercuric chloride, is manufactured by heating 2 parts by 
weight of mercury with 3 parts of strong sulphuric acid, and evaporating 
to dryness, to obtain mercuric sulphate (Hg + 2 H 2 S0 4 = HgS0 4 + 2 H 2 G 
+ S0 2 ), which is mixed with 1 \ part of common salt and heated in 
glass vessels (HgS0 4 + 2NaCl = ]STa 2 S0 4 + HgCl.,), when sodium sulphate 
is left, and the corrosive sublimate is converted into vapour, condensing 
on the cooler part of the vessel in lustrous colourless masses which are 
very heavy (sp. gr. 5*4), and have a crystalline fracture. It fuses very 
easily (at 509° F.) to a perfectly colourless liquid, which boils at 563° F., 
emitting an extremely acrid vapour, which destroys the sense of smell 
for some time. The specific gravity of its vapour is 140 (H = l) ; and 
that calculated from the formula HgCl.? is 135 - 5. This vapour condenses 
in fine needles, or sometimes in octaheclra. Corrosive sublimate dissolves 
in three times its weight of boiling water, but requires 16 parts of cold 
water, so that the hot solution readily deposits long four- sided prismatic 
crystals of the salt. It is remarkable that alcohol and ether dissolve 
corrosive sublimate much more easily than water, boiling alcohol dissolving 
about an equal weight of the chloride, and cold ether taking up one-third 
of its weight. By shaking the aqueous solution with ether, the greater 
part of the corrosive sublimate will be removed, and will remain dissolved 
in the ether which rises to the surface. Water in which sal-ammoniac 
has been dissolved will take up corrosive sublimate more easily than pure 
water, a soluble double chloride (sal alembroth) being formed, which may 
be obtained' in tabular crystals of the composition HgCl 2 .6^N"H 4 Cl,H 2 0. 

* Two volumes of vapour of corrosive sublimate contain 2 volumes of mercmy vapour 
l^ee note to page 384) and 2 volumes of chlorine. 



CALOMEL OR MEECUROUS CHLORIDE. 389 

A solution of corrosive sublimate in water containing sal-atnnioniac is a 
very efficacious bug-poison. 

The poisonous properties of corrosive sublimate are very marked, so 
little as three grains having been known to cause death in the case of a 
child. The white of egg is commonly administered as an antidote, because 
it is known to form an insoluble compound with corrosive sublimate, so 
as to render the poison inert in the stomach. The compound of albumen 
with corrosive sublimate is also much less liable to putrefaction than 
albumen itself, and hence corrosive sublimate is sometimes employed for 
preserving anatomical preparations and for preventing the decay of wood 
(by combining with the vegetable albumen of the sap). 

Mercuric chloride unites with many other chlorides to form soluble 
double salts, and with mercuric oxide, forming several oxy chlorides, 
which have no useful applications. 

White precipitate, employed for destroying vermin, is deposited when 
a solution of corrosive sublimate is poured into an excess of solution of 
ammonia : HgCl 2 + 2Is T H 3 = NH 4 C1 + KB 2 Hg"Cl (white precipitate). 

The true constitution of white precipitate has been the subject of much discussion, 
hut the changes which it undergoes, under various circumstances, appear to lead to 
the conclusion that it represents ammonium chloride, NH 4 C1, in which half of 
the hydrogen has been displaced by mercury. When boiled with potash, it yields 
ammonia and mercuric oxide, XH 2 Hg"Cl + KHO = iS"H 3 + HgO + KCl. If it be 
boiled with water, it is only partly decomposed in a similar manner, leaving a yellow 
powder having the composition (NH o HgCl).Hg0, produced according to the ecpiation 
2(XH 2 HgCl) + H 2 = XH 4 C1 + (NH 2 HgCl). HgO. A compound corresponding to this 
yellow precipitate, but containing mercuric chloride in place of oxide, is precipitated 
when ammonia is gradually added to solution of corrosive sublimate in large excess, 
the result being a compound of white precipitate with a molecule of undecomposed 
mercuric chloride, (XH 2 HgCl).HgCl 2 . 

If white precipitate be heated to about 600° F. , it evolves ammonia, and yields a 
sublimate of ammoniated mercuric chloride, HgCl 2 .XH 3 , leaving a red crystalline 
powder which is insoluble in water and in diluted, acids, and is unchanged by boiling 
with potash ; it may be represented as a compound of mercuric chloride with 
ammonia, in which the whole of the hvdrogen has been displaced by mercury, 
X 2 Hg : /'.2HgCl 2 . 

When solution of corrosive sublimate is added to a hot solution of sal-ammoniac, 
mixed with ammonia, a crystalline deposit is obtained on cooling the liquid, which 
is known as fusible tuhite pretiiritate, and represents two molecules of ammonium 
chloride, in which one-fourth of the hydrogen has been displaced by mercury, its 
composition being N 2 H 6 Hg"Cl 2 . The same compound is formed when white precipi- 
tate is boiled with solution of sal-ammoniac, NH 2 Hg"Cl + NH 4 Cl = X 2 H 6 Hg"Cl 2 . 

The above compounds possess a special interest for the chemist, as they were 
among the first to attract attention to the mobility of the hydrogen in ammonia, 
which has since been so well exemplified in the artificial production of organic bases 
by the action of ammonia upon the iodides of the alcohol-radicals. The relation of 
these compounds to each other is here exhibited : — 

White precipitate, NH 2 Hg' / Cl 

Produced with corrosive sublimate in excess, . (XH 2 HgCl).HgCl 2 

by boiling with water, . . . (NH 2 HgCl).HgO 

,, ,, sal-ammoniac, . . N. 2 H fi Hg"Cl 2 

,, by heating to 600° F., : . . (N 2 Hg 3 ".2HgCl 2 ) . 

291. Calomel, subchloride or protochloride of mercury, or mercurous 
chloride (HgCl),* unlike corrosive sublimate, is insoluble in water, so 

* That this is the correct formula, and not Hg 2 CL, has been recently proved by the 
experiments of Fileti on the vapour-density of a mixture of mercurous and mercuric 
chlorides. 



390 IODIDES OF MERCURY. 

that^it is precipitated when hydrochloric acid or a soluble chloride is 
added to mercurous nitrate. The simplest mode of manufacturing it 
consists in intimately mixing a molecular weight of corrosive sublimate 
with an atomic weight of metallic mercury, a little water being added to 
prevent dust, drying the mixture thoroughly, and subliming it; HgCl 2 
+ Hg = 2HgCl. But it is more commonly made by adding another 
atomic weight of mercury to the materials employed in the preparation of 
corrosive sublimate. Two parts by weight of mercury are dissolved, with 
the aid of heat, in 3 parts of oil of vitriol, and evaporated to dryness ; 
Hg + 2H 2 S0 4 = HgS0 4 + S0 2 + 2H 2 0. The residue of mercuric sulphate 
is intimately mixed with two more parts of mercury, and the mixture 
afterwards triturated with 1| parts of common salt, until globules are no 
longer visible. The mixture is then heated, so that the calomel may 
pass off in vapour, which condenses as a translucent fibrous cake on 
the cool part of the subliming vessel, leaving sodium sulphate behind ; 
HgS0 4 + Hg + 2NaCl = 2HgCl + Na 2 S0 4 . For medicinal purposes the 
calomel is obtained in a very fine state of division by conducting the 
vapour into a large chamber so as to precipitate it in a fine powder by 
contact with a large volume of cold air. Steam is sometimes introduced 
to promote its fine division. Sublimed calomel always contains some 
corrosive sublimate, so that it must be thoroughly washed with water 
before being employed in medicine. When perfectly pure calomel is 
sublimed, a little is always decomposed during the process into metallic 
mercury and corrosive sublimate. 

Calomel is met with either as a semi-transparent fibrous mass, or an 
amorphous powder, with a slightly yellow tinge. It is heavier than 
corrosive sublimate (sp. gr. 7*18), and does not fuse before subliming; 
it may be obtained in four-sided prisms by slow sublimation. Diluted 
acids will not dissolve it, but boiling nitric acid gradually converts it 
into mercuric chloride and nitrate, which pass into solution. Boiling 
hydrochloric acid turns it grey, some mercury being separated, and 
mercuric chloride dissolved. Mercuric nitrate dissolves it, forming mercuric 
chloride and mercurous nitrate. Alkaline solutions convert it into 
black mercurous oxide, as is seen in black-wash, made by treating calomel' 
with lime-water (2HgCl + Ca(OH) 2 = Hg 2 + CaCl 2 + H 2 0). Solution of 
ammonia converts it into a grey compound (NH 2 Hg 2 Cl), which is the 
analogue of white precipitate (NH 2 Hg"Cl), containing Hg 2 in place 
of Hg". 

Mercurous iodide (Hgl) is a green unstable substance, formed when iodine is 
triturated with an excess of mercury and a little alcohol. The beautiful scarlet 
mercuric iodide (Hgl 2 ) has been noticed at p. 178. Its vapour has the remarkably 
high specific gravity 15 '68 (air = l). The iodide dissolves in ether and in alcohol. 

If mercuric iodide be dissolved in potassium iodide, the solution mixed with 
potash, and some ammonia added, a brown precipitate is formed, which may be 
represented by the formula NHg" 2 I.H 2 0; its formation can be explained by the 
equation, 2HgI 2 + 3KHO + NH 3 = NHg 2 I. H 2 + 3KI + 2H 2 Q. 

A solution of mercuric iodide in potassium iodide, mixed with potash, is employed 
as one of the most delicate tests (Nesslers test) for ammonia in waters ; x^- grain of 
ammonia in half a pint of water is distinctly recognised by the brown-yellow tinge 
caused by this test. 

292. Sulphides of mercury. — When mercury is triturated with sulphur, 
the black subsulphide of mercury or mercurous sulphide (Hg 2 S) is 
formed; it was termed by old writers Ethiop's mineral, and is an 



VERMILION OK MERCURIC SULPHIDE. 391 

unstable compound easily resolvable into metallic mercury and mercuric 
sulphide (HgS). The latter has been mentioned as the principal ore of 
mercury, and is important as composing vermilion. The native mercuric 
sulphide, or cinnabar, is found sometimes in amorphous masses, some- 
times crystallised in six-sided prisms varying in colour from dark brown 
to bright red. It may be distinguished from most other minerals by its 
great weight (sp. gr. 8*2), and by its red colour when scraped with a 
knife. Neither hydrochloric nor nitric acid, separately, will dissolve it, 
but a mixture of the two dissolves it as mercuric chloride, with separa- 
tion of sulphur. Some specimens of cinnabar have a bright red colour, 
so that they only require grinding and levigating to be used as vermilion ; 
and if the brown cinnabar in powder be heated for some time to 120° F. 
with a solution of sulphur in potash, it is converted into vermilion. 

Of the artificial mercuric sulphide there are two varieties, the black, 
which is precipitated when corrosive sublimate is added to hydro- 
sulphuric acid or a soluble sulphide, and the red (vermilion), into which 
the black variety is converted by sublimation, or by prolonged contact 
with solutions of alkaline sulphides containing excess of sulphur, though, 
so far as is known, the conversion is effected without chemical change, 
the red sulphide having the same composition as the black. In Idria 
and Holland, 6 parts of mercury and 1 of sulphur are well agitated 
together in revolving casks for several hours, and the black sulphide 
thus obtained is sublimed in tall earthen pots closed with iron plates, 
when the vermilion is deposited in the upper part of the pots, and is 
afterwards ground and levigated. The sublimed vermilion, however, 
is generally inferior to that obtained by the wet process, of which there 
are several modifications. One of the processes consists in triturating 
300 parts of mercury with 114 parts of sulphur- for two or three hours, 
and digesting the black product, at about 120° F., with 75 parts of 
caustic potash and 400 of water until it has acquired a fine red 
colour. The permanence of vermilion paint is, of course, attributable to 
the circumstance that it resists the action of light, of oxygen, carbonic 
acid, aqueous vapour, and even of the sulphuretted hydrogen, and sul- 
phurous or sulphuric acid which contaminate the air of towns, whereas 
the red paints containing lead are blackened by sulphuretted hydrogen, 
and all vegetable and animal reds are liable to be bleached by atmospheric 
oxygen and by sulphurous acid. 

When the black precipitated mercuric sulphide is boiled with solution 
of corrosive sublimate, it is converted into a white chlorosulphide of 
mercury, HgCl 2 .2HgS, which is also formed when a small quantity of 
hydrosulphuric acid is added to corrosive sublimate. 
• It is remarkable that the molecule of vermilion, HgS, occupies 3 
volumes instead of 2, containing 2 volumes of mercury vapour combined 
with 1 volume of sulphur vapour. The anomaly might be explained on 
the supposition that the high temperature requisite to convert the ver- 
milion. into vapour suffices to suspend the attraction between its elements, 
so that the vapour of which the specific gravity is taken is not really 
that of the compound of mercury and sulphur (which should occupy 2 
volumes), but a mixture of the 2 volumes of mercury vapour and 1 
volume of sulphur vapour, occupying 3 volumes. This view of the tem- 
porary decomposition of the vapour receives some slight support from the 
convertibility of the black into the red sulphide by sublimation. 



392 EXTRACTION OF PLATINUM. 

PLATINUM. 

Pt = 197*1 parts by weight. 

293. Platinum (platina, Spanish diminutive of silver) is always found 
in the metallic state distributed in flattened grains through alluvial de- 
posits similar to those in which gold is found ; indeed, these grains are 
generally accompanied by grains of gold, and of a group of very rare 
metals only found in platinum ores, viz., palladium, iridium, osmium, 
rhodium, and ruthenium. Russia furnishes the largest supply of platinum 
from the Ural Mountains, but smaller quantities are obtained from Brazil, 
Peru, Borneo, Australia, and California, 

The process for obtaining the platinum in a marketable form is rather 
a chemical than a metallurgic operation. The ore, containing the grains 
of platinum and the associated metals, is heated with a dilute mixture 
of hydrochloric and nitric acids, by which the platinum is converted into 
perchloride of platinum (PtCl 4 ) and dissolved, whilst the iridium and 
osmium are left in the residue. The solution is then mixed with some 
chloride of ammonium, which combines with the perchloride of platinum 
to form a yellow insoluble salt (ammonio-chloride of platinum 2NH 4 C1. 
PtCl 4 ).* This precipitate is collected, washed, and heated to redness, 
when all its constituents, except the platinum, are expelled in the form 
of gas, that metal being left in the peculiar porous condition in which it 
is known as spongy platinum. To convert this into compact platinum is 
by no means an easy task, on account of the infusibility of the metal, for ' 
it remains solid at the very highest temperatures of our furnaces. The 
spongy platinum is finely powdered in a wooden mortar (as it would 
cohere into metallic spangles in one of a harder material) and rubbed to a 
paste with, water; this paste is then rubbed through a sieve to render it 
perfectly smooth and uniform, and introduced into a cylinder of brass, in 
which it is subjected to pressure so as to squeeze out the water, and cause 
the minute particles of platinum to cohere into a somewhat compact disk; 
this disk is then heated to whiteness, and beaten into a compact metallic 
ingot by a heavy hammer; it is then ready for forging. 

This method is now modified by fusing the ore with 6 parts of lead, and treating- 
the alloy with dilute nitric acid (1:8) which dissolves most of the lead, together with 
copper, iron, palladium, and rhodium. The residue, containing platinum, lead, and 
iridium, is treated with dilute aqua regia, which leaves the iridium undissolved. 
The lead is precipitated by sulphuric acid, and the solution ot platinic chloride treated 
as above. 

Another process for obtaining platinum from its ores is based upon the tendency 
of this metal to dissolve in melted lead. The platinum ore is fused in a small 
reverberatory furnace, with an equal weight of sulphide of lead and the same quantity 
of oxide of lead, when the sulphur and oxygen escape as sulphurous acid gas, and 
the reduced lead dissolves the platinum, leaving undissolved a very heavy alloy of 
osmium and iridium, which sinks to the bottom. The upper part of the alloy of 
lead and platinum is then ladled out and cupelled (page 370), when the latter metal 
is left in a spongy condition, the lead being removed in the form of oxide. The 
platinum is then fused by the aid of the oxyhydrogen blowpipe, in a furnace made of 
lime (fig. 273), whence it is poured into an ingot mould made of gas carbon. The 
melted platinum absorbs oxygen mechanically like melted silver, and evolves it again 
on cooling (see page 371). Platinum articles are now frequently made from the fused 
metal, instead of from that which has been welded. 

* When rhodium is present, the liquid from which this precipitate has been deposited 
will have a rose colour. The precipitate is then mixed with bisulphate of potassium and 
a little bisulphate of ammonium, and heated to redness in a platinum dish. The rhodium 
is then converted into a double sulphate of rhodium and potassium, which may be removed 
from the spongy platinum by boiling with water. 



PROPERTIES OF PLATINUM. 



393 




Fig. 273. 



Its resistance to the action of high temperatures and of most chemical 
agents, renders platinum of the greatest service in chemical operations. 
It will be remembered that platinum stills are employed, even on the 
large scale, for the concentration of sulphuric acid. In the form of 
basins, small crucibles, foil, and wire, this 
metal is indispensable to the analytical 
chemist. Unfortunately, it is softer than 
silver, and therefore ill adapted for wear, 
and is so heavy (sp. gr. 21*5) that even 
small vessels must be made very thin in order 
not to be too heavy for a delicate balance. 
Since it expands less than any other metal 
when heated^ wires of platinum may be sealed 
into glass without danger of splitting it by 
unequal contraction. Its malleability and 
ductility are very considerable, so that it is 
easily rolled into thin foil and drawn into 
fine wires ; in ductility it is surpassed only 
by gold and silver, and it has been drawn, 

by an ingenious contrivance of Wollaston's, into wire of only ^^tli 
of an inch in diameter, a mile of which (notwithstanding the high 
specific gravity of the metal) would only weigh a single grain. This 
remarkable extension of the metal was effected by casting a cylinder 
of silver around a very thin platinum wire obtained by the ordinary 
process of wire-drawing ; when the cylinder of silver, with the platinum 
wire in its centre, was itself drawn out into an extremely thin wire, of 
course the platinum core would have become inconceivably thin, and 
when the silver casing was dissolved off by nitric acid, this minute fila- 
ment of platinum was left. Platinum is sometimes employed for the 
touch-holes of fowling-pieces on account of its resistance to corrosion. A 
little iridium is sometimes added to platinum in order to increase its 
elasticity. An alloy of 4 parts platinum, 3 parts silver, and 1 part copper 
is used for pens. 

The remarkable power possessed by platinum, of inducing chemical 
combination between oxygen and other gases, has already been noticed. 
Even the compact metal possesses this property, as may be seen by heat- 
ing a piece of platinum foil to redness in the flame of a gauze gas-burner 
rapidly extinguishing the gas, and turning it on again, when the cold 
stream of gas will still maintain the metal at a red heat, 
in consequence of the combination with atmospheric 
oxygen at the surface of the platinum. 

A similar experiment may be made by suspending a 
coil of platinum wire in the flame of a spirit-lamp (tig. 
274), and suddenly extinguishing the flame when the 
metal is intensely heated, by placing the mouth of a test- 
tube over it; the wire will continue to glow by inducing 
the combination of the spirit vapour with oxygen on its 
surface. By substituting a little ball of spongy platinum 
for the coil of platinum wire, and mixing some fragrant essential oil with 
the spirit, an elegant perfuming lamp has been contrived. Upon the same 
principle an instantaneous light apparatus has been made, in which a jet 
of hydrogen gas is kindled by falling upon a fragment of cold spongy 




394 OXIDES OF PLATINUM. 

platinum, which at once ignites it by inducing its . combination with the 
oxygen condensed within the pores of the metal. Spongy platinum is 
obtained in a very active form by heating the ammonio-chloride of 
platinum very gently in a stream of coal gas or hydrogen as long as any 
fumes of hydrochloric acid are evolved. 

If platinum be precipitated in the metallic state from a solution, it is 
obtained in the form of a powder, called platinum-black, which possesses 
this power of promoting combination with oxygen in the highest perfec- 
tion. This form of platinum may be obtained by dissolving the metal 
in aqua regia, which converts it into platinic chloride (PtCLJ, evaporating 
the solution to dryness, and heating the residue gently on a sand-bath 
as long as it smells strongly of chlorine. The platinous chloride (PtCl 2 ) 
thus obtained is dissolved in a solution of potash and heated with alcohol, 
when the platinum-black is precipitated, and must be filtered off, washed, 
and dried at a gentle heat. 

Platinum in this form is capable of absorbing 800 times its volume of 
oxygen, which does not enter into combination with it, but is simply 
condensed into its pores, and is available for combination with other bodies. 
A jet of hydrogen allowed to pass on to a grain or two of this powder is 
kindled at once, and if a few particles of it be thrown into a mixture of 
hydrogen and oxygen, explosion immediately follows. A drop of alcohol 
is also inflamed when allowed to fall upon a little of the powder. 
Platinum black loses its activity after having been heated to redness. 
Recent experiments by Berthelot indicate that platinum black is really 
an oxide. 

Although platinum resists the action of hydrochloric and nitric acids, 
unless they are mixed, and is unaffected at the ordinary temperature by 
other chemical agents, it is easily attacked at high temperatures by phos- 
phorus, arsenic, carbon, boron, silicon, and by a large number of the 
metals; the caustic alkalies and alkaline earths also corrode it, so that 
some discretion is necessary in the use of vessels made of this costly 
metal. When platinum is alloyed with 10 parts of silver, both metals 
may be dissolved by nitric acid. 

294. Oxides- of platinum. — Only one compound of platinum with 
oxygen is known in the separate state, the other having been obtained 
in combination with water. Platinous oxide, PtO, is precipitated as a 
black hydrate by decomposing platinous chloride with potash, and 
neutralising the solution with dilute sulphuric acid. It is a feeble base, and 
decomposes when heated, leaving metallic platinum. Platinic oxide, Pt0 2 , 
is also a weak base, but occasionally plays the part of an acid, whence it 
is sometimes termed platinic acid. Platinate of soda (]Sa 2 0.3Pt0 2 .6Aq.) 
may be crystallised from a solution of the hydrated binoxide in soda. 
Platinate of lime is convenient for the separation of platinum from 
iridium, which is generally contained in the commercial metal; for this 
purpose, the platinum is dissolved in nitre-hydrochloric acid, the solution 
evaporated till it solidifies on cooling, the mixed chlorides of iridium and 
platinum dissolved in water, and decomposed with an excess of lime 
without exposure to light; the platinum then passes into solution as 
platinate of lime, and the platinic acid may be separated from the filtered 
solution, though still in combination with lime, by exposure to light. 
Acids dissolve platinic oxide, forming salts of a brown colour which have 



CHLOKIDES OF PLATINUM. 395 

not been crystallised. If the oxide be dissolved in diluted sulphuric acid 
and the solution mixed with excess of ammonia, a black precipitate of 
fulminating platinum is obtained, which detonates violently at about 
400° F. This compound is said to have a composition corresponding to 
the formula !N~ 2 H Pt iv . 4TI 2 0, or a combination of water with a double 
molecule of ammonia (N 2 H 6 ), in which 4 atoms of hydrogen are replaced 
by 1 atom of tetratomic platinum. 

Chlorides of platinum. — The perchloride, or platinic chloride (PtCl 4 ), is 
the most useful salt of the metal, and may be prepared by dissolving 
scraps of platinum foil in a mixture of four measures of hydrochloric acid 
with one of nitric acid (100 grs. of platinum require 2 measured ounces 
of hydrochloric acid), evaporating the liquid at a gentle heat to the con- 
sistence of a syrup, redissolving in hydrochloric acid, and again evapor- 
ating to expel excess of nitric acid. The syrupy liquid solidifies, on 
cooling, to a red-brown mass, which is very deliquescent, and dissolves 
easily in water or alcohol to a red brown solution. If the concentrated 
solution be allowed to cool before all the free hydrochloric acid has been 
expelled, long brown prismatic crystals of a combination of platinic chloride 
with hydrochloric acid are obtained (PtCl 4 .2HCl.6Aq). Platinic chloride is 
remarkable for its disposition to form sparingly soluble double chlorides 
with the chlorides of the alkali metals and the hydrochlorates of organic 
bases, a property of great value to the chemist iu effecting the detection 
and separation of these bodies. 

A good example of this has lately been afforded in the separation of 
potassium, rubidium, and caesium. The chlorides of these three metals 
having been separated from the various other salts contained in the 
mineral water in which they occur, are precipitated with platinic chloride 
which forms combinations with all the three' chlorides. The platino- 
chloride of potassium is more easily dissolved by boiling water than those 
of rubidium and caesium, and is removed by boiling the mixed precipitate 
with small portions of water as long as the latter acquires a yellow colour. 
The remaining platinu-chlorides of rubidium and caesium are then heated 
in a current of hydrogen, which reduces the platinum to the metallic state, 
and the chlorides may then be extracted by water, in which they are very 
soluble. 

P latino-chloride of potassium (2KCl,PtCl 4 ) forms minute yellow octa- 
hedral crystals ; those of rubidium and caesium have a similar composition 
and crystalline form. 

Platino -chloride of sodium differs from these in being very soluble in 
water and alcohol ; it may be crystallised in long red prisms, having the 
composition 2XaCl,PtCl 4 ,6Aq. 

Ammonio-chloride of platinum (2NH 4 Cl.PtG 4 ) has been already noticed 
as the form in which platinum is precipitated in order to separate it from 
other metals. It crystallises, like the potassium-salt, in yellow octahedra, 
which are very sparingly soluble in water and insoluble in alcohol. It 
is the form into which nitrogen is finally converted in analysis in order to 
determine its weight, "When heated to redness, this salt leaves a residue 
©f spongy platinum. Platinic chloride is sometimes used for browning 
gun-barrels, &c., under the name of muriate of platina. 

Protochloride of platinum or platinous chloride (PtCl 2 ). — Platinic chloride may be 
heated to 450° F. without decomposition, but above that temperature it evolves 
chlorine, and is slowly converted into the platinous chloride, which is reduced, at 



396 PLATOSAMINE COMPOUNDS. 

a much higher temperature, to the metallic state. Platinous chloride forms a dingy 
green powder, which is insoluble in water and in nitric and sulphuric acids, but 
dissolves in hot hydrochloric acid, and in solution of platinic chloride, yielding in 
the former a bright red, in the latter a very dark brown-red solution. Its solution 
in hydrochloric acid is not precipitated by potassium chloride, but a soluble double 
chloride (2KCl,PtCl 2 ) may be crystallised from the liquid. If ammonium chloride 
be added to the hydrochloric solution, a double salt 2NH 4 Cl.PtCl 2 may be obtained 
in yellow crystals by evaporation. If, instead of ammonium chloride, free ammonia 
be added in excess to the boiling solution of platinous chloride in hydrochloric acid, 
brilliant green needles (green salt of Magnus) are deposited on cooling, which con- 
tain the elements of platinous chloride and ammonia PtCl 2 (NH 3 ) 2 ; but from the 
behaviour of this compound with chemical agents, its true formula would appear to 
be N 2 H 6 Pt"Cl 2 , in which the place of 2 atoms of hydrogen in 2 molecules of sal- 
ammoniac is occupied by platinum. By heating this salt with an excess of ammonia, 
the solution, on cooling, deposits yellowish-white prismatic crystals of hydrochloratc 
of diplatosamine ; N 4 H 10 Pt".2HCl. Aq., the production of which may be represented 
by the equation N 2 H 6 Pt"Cl 2 + 2NH 3 = N 4 H 10 Pt".2HCl. By decomposing a solution 
of this salt with silver sulphate, the sulphate of diplatosamine is obtained; N 4 H 10 Pt". 
2HC1 + Ag 2 O.S0 3 = N 4 H 1? Pt". H 2 0. S0 3 + 2 AgCl. 

When the solution of diplatosamine sulphate is treated with barium hydrate, 
barium sulphate is precipitated, and a powerfully alkaline solution is obtained, 
which yields crystals of diplatosamine hydrate N 4 H ]0 Pt".2H 2 O, a strong alkali 
which may be regarded as a compound of water with 4 molecuksof ammonia (N 4 H 12 ), 
in which. 2 atoms of hydrogen are replaced by platinum. The diplatosamine hydrate 
has a strong resemblance to the alkalies, eagerly absorbing carbonic acid from the 
air, and expelling ammonia from its salts. When the hydrate of diplatosamine is 
heated to 230° F. it gives oft" water and ammonia, and becomes converted into a grey 
insoluble substance, which is platosamine hydrate, N 2 H 4 Pt". H 2 0, and may be 
regarded as a compound of water with a double molecule of ammonia (N 2 H 6 ), in 
which one-third of the hydrogen is replaced by platinum. This substance is also a 
base, and forms salts, most of which are insoluble ; the sulphate of platosamine, 
N 2 H 4 Pt.H 2 O.S0 3 .Aq., may be regarded as ammonium sulphate (NH 4 ) 2 S0 4 , in which 
2 atoms of the hydrogen are replaced by platinum. The hydrochlorate of platosamine 
(N 2 H 4 Pt.2HCl) is isomeric with the green salt of Magnus, and may be obtained 
from that compound by dissolving it in a hot solution of ammonium sulphate 
from which it crystallises on cooling.* 

If the platosamine hydrochlorate, suspended in boiling water, be treated with 
chlorine, it is converted into platinamine hydrochlorate, N 2 H 2 Pt iv .4HCl, which may 
be represented as ammonium chloride, . in which 4 atoms of hydrogen have been 
replaced by 1 atom of platinum in the condition in which it exists in PtCl 4 , where 
it is equivalent to H 4 . The conversion of the platosamine hydrochlorate into 
platinamine hydrochlorate may be represented by the equation, N 2 H 4 Pt.2HCl + Cl 2 
= N 2 H 2 Pt.4HCl. By boiling the hydrochlorate of platinamine with silver nitrate, 
it is converted into platinamine nitrate N 2 H 2 Pt(HjSi"03) 4 , and when this is dissolved 
in boiling water and decomposed by ammonia the platinamine hydrate (N 2 H 2 Pt,4H 2 0), 
is obtained in yellow prismatic crystals, having the same composition as that assigned 
to fulminating platinum. 

Several other platinum compounds derived from ammonia have been obtained, but 
cannot at present be so conveniently classified. The following table exhibits the 
composition of those here enumerated, the platinum, as it exists in platinous chloride 
(PtCl 2 ), occupying the place of 2 atoms of hydrogen, being'represented by Pt", and 
the platinum, as it exists in platinic chloride (PtCl 4 ) occupying the place of 4 atoms 
of hydrogen, by Pt iv : — 

Platosamine hydrate, . . N 2 H 4 Pt".H 2 

hvdrochlorate, . N 2 H 4 Pt".2HCl 
sulphate, . . N 2 H 4 Pt".H 2 S0 4 Aq. 

Platinamine hydrate, . . N 2 H 2 Pt iy .4H 2 

hydrochlorate, . N 2 H 2 Pfv.4H(Jl 

* The salts of diplatosamine are distinguished from those of platosamine by the action of 
nitrous acid, which gives a fine blue or green precipitate or coloration with the former. For 
the cause of this change, and for many other interesting points in the history of these pla- 
tinum compounds, the reader is referred to the elaborate and accurate memoir by Hadow. — 
Journal of the Chemical Society, August 1866. 



PALLADIUM — RHODIUM. 397 

Diplatosamine hydrate, . . X 4 H 10 Pt". 2H 2 

hydrochlorate, . 2s T 4 H 10 Pt".2HCl.Aq. 
sulphate, . . K 4 H 10 Pt". H 2 S0 4 

Some of the salts of diplatinamine (jST 4 H g Pt IV ) have been obtained, this base being 
derived from 4 molecules of ammonia in which H 4 have been replaced by Pt iv . 

The sulphides of platinum correspond in composition to the oxides and chlorides, 
and may be obtained by the action of hydrosulphuric acid upon the respective chlo- 
rides, as black .precipitates. 

295. Palladium (Pd = 106*5) is found in small quantity associated with native 
gold and platinum. It presents a great general resemblance to platinum, but is dis- 
tinguished from it by being far more easily oxidised, and by its special attraction for 
cyanogen, with which it forms an insoluble compound. This circumstance is taken 
advantage of in separating palladium from the platinum ores, for which purpose the 
solution from Avhich the greater part of the platinum has been precipitated by 
ammonium chloride (page 392) is neutralised with sodium carbonate, and mixed with 
solution of mercuric cyanide Hg(OISr) 2 , when a yellowish precipitate of palladium 
cyanide is obtained, yielding spongy palladium when heated, which may be welded 
into a compact form in the same manner as platinum. When alloyed with native 
gold, palladium is separated by fusing the alloy with silver, and boiling it with nitric 
acid, which leaves the gold undissolved. The silver is precipitated from the solu- 
tion as chloride, by adding sodium chloride, and metallic zinc is placed in the liquid, 
which precipitates the palladium, lead, and copper, as a black powder. This is 
dissolved in nitric acid, and the solution mixed with an excess of ammonia, which 
precipitates the lead oxide, leaving the copper and palladium in solution. On adding 
hydrochloric acid in slight excess, a yellow precipitate of palladamine hydrochlorate 
(N 2 H 4 Pd, 2HC1) is obtained, which leaves metallic palladium when heated. 

Palladium is harder than platinum and much lighter (sp. gr. 11 - 5) ; it is malleable 
and ductile like that metal, and somewhat more fusible, though it cannot be melted 
in an ordinary furnace.* It is unchangeable in air unless heated, when it becomes 
blue from superficial oxidation, but regains its whiteness when further heated, the 
oxide being decomposed. Unlike platinum, it may be dissolved by nitric acid, form- 
ing palladium nitrate, Pd(N0 3 ) 2 , which is sometimes employed in analysis for pi-e- 
cipitating iodine from the iodides, in the form of black palladium iodide (Pdl 2 ). 
Palladium is useful, on account of its hardness, lightness, and resistance to tarnish. 
in the construction of philosophical instruments ; alloyed with twice its weight of 
silver, it is used for small weights. 

Of the oxides of palladium, two correspond with those of platinum, and a basic 
oxide (PdO) has been obtained hj gently heating the dioxide. Palladia chloride 
(PdCl 4 ) is very unstable, being easily decomposed, even in solution, into palla- 
dious chloride (PdCl 2 ) and free chlorine. Both the chlorides form double salts 
with the alkaline chlorides, those containing the palladious chloride (PdCl 2 ) having 
a dark green colour. Pulverulent palladium carbide is formed when the metal is 
heated in the flame of a spirit-lamp. 

296. Rhodium (Ro = 104 - 3), another of the metals associated with the ores of 
platinum, has acquired its name from the red colour of many of its salts {poSou, a rose). 
It is obtained from the solution of the ore in aqua regia by precipitating the platinum 
with ammonium chloride, neutralising with sodium carbonate, adding mercuric 
cyanide to separate the palladium, and evaporating the filtered solution to dryness 
with excess of hydrochloric acid. On treating the residue with alcohol, the double 
chloride of rhodium and sodium is left undissolved as a red powder. By heating this 
in a tube through which hydrogen is passed, the rhodium is reduced to the metallic 
state, and the sodium chloride may be washed out with water, leaving a grey powder 
of metallic rhodium, which is fused by the oxjdiydrogen blowpipe with greater 
difficulty than platinum, and forms a very hard malleable metal not dissolved even 
by aqua regia, although this acid dissolves it in ores of platinum, because it is 
alloyed with other metals. If platinum be alloyed with 30 percent, of rhodium, 
however, it is not affected by aqua regia,, which will probably render the alloy useful 
for chemical vessels. Rhodium may be brought into solution by fusing it with bisul- 

* Palladium, at a slightly elevated temperature, absorbs, mechanically, many times its 
volume of hydrogen. Hammered palladium foil condenses 640 times its volume of hydro- 
gen, below 212° Y., though it has not the power of absorbing oxygen or nitrogen. Foil 
made from fused palladium only absorbs 68 times its volume of hydrogen.— Graham. Proc. 
Roy. Soc., June 1866. 



398 OSMIUM — RUTHENIUM. 

phate of potash, when sulphurous acid gas escapes, and a double sulphate of rhodium 
and potassium is formed, which gives a pink solution with water. Finely-divided 
rhodium is oxidised when heated in air. It appears to form two oxides, the prot- 
oxide (RoO), which is very little known, and the sesquioxide (Ro 2 3 ), obtained by fus- 
ing rhodium with potassium carbonate and nitre, and washing the fused mass with 
water, which leaves an insoluble compound of the sesquioxide with potash ; on treat- 
ing this with hydrochloric acid, the sesquioxide of rhodium is left. It is not decom- 
posed by heat, and is insoluble in acids, though it is a basic oxide, and its salts, 
which have a red colour, are obtained by indirect methods. 

Trichloride of rhodium (RoCl 3 ) has a brownish-black colour, and does not crystal- 
lise. Its aqueous solution is red, and it forms crystallisable double salts with the : 
alkaline chlorides, which have a fine red colour. The double chloride of rhodium 
and sodium (3NaCl.RoCl 3 ).9Aq., is prepared by heating a mixture of pulverulent 
rhodium and sodium chloride in a current of chlorine. It crystallises in red octa- 
hedra. On boiling a solution of trichloride of rhodium with ammonia in excess, a 
yellow ammoniated salt (RoCl 3 .5NH 3 ) may be crystallised out, from which metallic 
rhodium may be obtained by ignition. 

With sulphur, rhodium combines energetically at a high temperature ; a proto- 
sulphide and a sesquisulphide have been obtained. 

An alloy of gold with between 30 and 40 per cent, of rhodium has been found in 
Mexico. 

297. Osmium (Os = 199) is characterised by its yielding a very volatile acid oxide 
(osmic anhydride, Os0 4 ), the vapours of which have a very irritating odour (65/^, 
odour). It occurs in the ores of platinum in flat scales, consisting of an alloy of 
osmium, iridium, ruthenium, and rhodium. This alloy is also found associated 
with native gold, and, being very heavy, it accumulates at the bottom of the crucible 
in which the gold is melted. The osmium alloy is extremely hard, and has been used 
to tip the points of gold pens. When a grain of it happens to be present in the gold 
which is being coined, it often seriously injures the die. When the platinum ore 
is treated with aqua regia, this alloy is left undissolved, together with grains of 
chrome-iron ore and titanic iron. To extract the osmium from this residue, it is 
heated in a porcelain tube through which a current of dry air is passed, when the 
osmium is converted into osmic anhydride, the vapour of which is carried forward 
by the current of air and condensed in bottles provided to receive it. The osmic 
anhydride forms colourless prismatic crystals which fuse and volatilise below the 
boiling-point of water, yielding a most irritating vapour resembling chlorine. It is 
very soluble in water, giving a solution which exhales the same odour and stains the 
skin black ; tincture of galls gives a blue precipitate with the solution. Its acid 
properties are feeble, for it neither reddens litmus nor decomposes the carbonates, 
and its salts are decomposed by boiling their solutions. By adding hydrosulphuric 
acid to a solution of osmic acid, the osmium tetrasulphide (OsS 4 ) is obtained as a black 
precipitate, and if this be carefully dried and heated in a crucible made of gas-carbon, 
metallic osmium is obtained as a brittle mass (sp. gr. 21'4), which is not fused even 
by the oxyhydrogen blowpipe, and is not soluble in acids. When obtained by other 
processes in a finely-divided state, osmium oxidises even at the ordinary temperature, 
and emits the odour of osmic anhydride. In this state, also, it may be dissolved by 
nitric acid, which converts it into osmic acid. 

By dissolving osmic anhydride in potash and adding alcohol, the latter is oxidised" 
at the expense of the potassium osmiate, and rose-coloured octahedral crystals of 
potassium osmite (K 2 0s0 4 ,2Aq.) are obtained ; the osmious acid has not been isolated. 
A protoxide and a dioxide of osmium have been obtained. 

Osmium appears to form four chlorides— dichloride (OsCl 2 ), trichloride (OsCl 3 ), 
tetrachloride (OsCl 4 ), and hexachloride (OsCl 6 ). The dichloride and tetrachloride are 
formed by the direct combination of chlorine with osmium ; the former sublimes in 
green needles, which yield a blue solution in water, soon absorbing oxygen from the- 
air and becoming converted into tetrachloride. By heating a mixture of pulverulent 
osmium with potassium chloride in a current of chlorine, a double chloride of osmium 
and potassium (2KCl,OsCl 4 ) is obtained, which is sparingly soluble, and crystallises 
in octahedra like the corresponding salt of platinum. When decomposed with silver 
nitrate it gives a dark green precipitate (2AgCl,OsCl 4 ). 

298. Ruthenium (Ru = 104*2).* — In the process of extracting osmium from the 

* A new mineral found in Borneo, and named laurite, contains sulphides of ruthenium 
and osmium. It forms small lustrous granules. 



ANALYSIS OF PLATINUM ORE. 



399 



residue left on treating the platinum ore with aqua reqia, by heating in a current of 
air, square prismatic crystals of ruthenium dioxide (Ru0 2 ) are deposited nearer to 
the heated portion of the tube than the osmic anhydride, for the dioxide is not itself 
volatile, being only carried forward mechanically. "When ruthenium dioxide is heated 
in hydrogen, metallic ruthenium is obtained as a hard, brittle, almost infusible metal, 
which is scarcely affected even by aqua regia. The protoxide of ruthenium (RuO) is 
a dark grey powder insoluble in acids. The sesquioxide (Ru 2 3 ) and the dioxide 
(Ru0 2 ) have feebly basic properties. The sesquioxide is not decomposed by heat. 
The anhydrous dioxide is a greenish-blue powder. Euthenic anhydride (Ru0 3 ) is 
known only in combination with bases. 

299. Iridium (Ir = 197'l), named from Iris, the rainbow, in allusion to the varied 
colours of its compounds, has been mentioned above as occurring in the insoluble 
alloy from the platinum ores. It is also sometimes found separately, and occasion- 
ally alloyed with platinum, the alloy crystallising in octahedra, which are even 
heavier than platinum (sp. gr. 22*3). If the insoluble osmiridium alloy left by aqua 
regia be mixed with common salt and heated in a current of chlorine, a mixture of 
the sodio-chlorides of the metals is obtained, and may be extracted by boiling water. 
If the solution be evaporated and distilled with nitric acid, the osmium is distilled 
off as osmic acid, and by adding ammonium chloride to the residual solution, the 
iridium is precipitated as a dark red-brown ammonio-coloride, 2NH 4 Cl.IrCl 4 , which 
leaves metallic iridium when heated. Like platinum, it then forms a grey spongy 
mass, but is oxidised when heated in air, and may be fused with the oxyhydrogen 
blowpipe to a hard brittle mass (sp. gr. 22*4), which does not oxidise in air. Like 
rhodium, it is not attacked by aqua regia, unless alloyed with platinum. The pro- 
duct of the oxidation of finely-divided iridium in air is the sesquioxide (lr 2 3 ), which 
is a black powder used for imparting an intense black to porcelain ; it is insoluble 
in acids. The 'protoxide (IrO) is also more easily acted upon by alkalies than by 
acids ; its solution in potash becomes blue when exposed to air, from the formation 



of the dioxide (Ir0 2 ). The trioxide (Ir0 3 ) is gre 



The dichloride (IrCl 2 ) and 



tetrachloride (IrCl 4 ) of iridium resemble the corresponding chlorides of platinum in 
forming double salts with the alkaline chlorides. There is also a trichloride (IrCl 3 ), 
the solution of which has a green colour, and gives a yellow precipitate with rner- 
curous nitrate, and a blue precipitate, soon becoming white, with silver nitrate. 
Iridium resembles palladium in its disposition to combine with carbon when heated 
in the flame of a spirit-lamp. 

An iridio-platinum alloy containing from 15 to 20 per cent, of iridium has been 
found very useful for making standard rules and weights, on account of its indestruc- 
tibility, extreme rigidity, hardness, and high density. 

300. The following table exhibits a general view of the analytical process by which 
the remarkable metals associated in the ores of platinum may be separated from 
each other, omitting the minor details which are requisite to ensure the purity of 
each metal : — 

Analysis of tlie Ore of Platinum. 

Boil with aqua regia. 



Dissolved. 
Platinum, Palladium, Rhodium. 

Add ammonium chloride. 


Undissolved. 
Iridium, Osmium, Ruthenium. 
Chrome iron, Titanic iron, «fec. 

Heat in current of dry air. 


Precipitated ; 
Platinum 

2NH 4 C1, PtCl 4 . 


Solution ; 

Neutralise with soda carbonate ; 

add mercuric cyanide. 


Volatilised 
Osmium 
as Os0 4 . 


Carried 
f orward by 
tlie current; 
Ruthenium 

as RuO». 


Residue ; 

Mix with sodiia/i 

chloride, and heat in 

current of chlorine. 

Treat with boiling water. 


Precipitated ; 
Palladium 
as PdCy._>. 


Solution ; 

Evaporate with 

hydrochloric acid 

Treat with alcohol. 

Insoluble. 

Rhodium 

as 3NaCl.RoCl 3 . 


Dissolved. 

Iridium 

as2NaCl.IrCl 4 . 


Residue. 

Titanic iron. 

Chrome iron, 

&c. 



The group of platinoid, metals exhibits some very remarkable features, and it is to 
be regretted that this group is comparatively imperfectly known in consequence of 



400 



GOLD. 



the difficulty and expense attendant upon the purification of the metals. Its mem- 
bers may be arranged in two divisions, the metals in each agreeing closely in their 
atomic weights and specific gravities. 





Atomic weight. 


Sp. gr. 




Atomic weight. 


Sp. gr. 


Platinum, 


197-1 


21-5 


Palladium, . 


106-5 


11 


Osmium, 


199-0 


22-4 


Rhodium, 


104-3 


11-4 


Iridium, 


197-1 


22'4 


Ruthenium, . 


104-2 


11-4 



Through osmium, this group of elements is connected Avith the group containing 
-antimony, arsenic, and phosphorus, which osmium resembles in the facility with 
which it is oxidised, and in the volatility of the oxide formed. Palladium connects 
it with mercury and silver, by its solubility in nitric acid, and its special attraction 
for cyanogen and iodine. 

301. Davyum is a new metal which has been found in small quantity in the ores 
of platinum. It is a silveiy metal which dissolves in aqua regia. The double 
chloride of davyum and sodium is nearly insoluble in water and alcohol, which dis- 
tinguishes davyum from the other platinum metals. Its solutions give a red colour 
with potassium sulphocyanide. The specific gravity of the metal is about 9*4. 



GOLD. 

Au = 196 "6 parts by weight. 

302. Gold is one of those few metals which are always found in the 
metallic state, and is remarkable for the extent to which it is distri- 
buted, though in small quantities, over the surface of the earth. The 
principal supplies of this metal are derived from Australia, California, 
Mexico, Brazil, Peru, and the Uralian Mountains. Small quantities 
have been occasionally met with in our own islands, particularly 
at Wicklow, at Cader Idris in "Wales, Leadhills in Scotland, and in 
Cornwall. 

The mode of the occurrence of gold in the mineral kingdom resembles 
that of the ore of tin, for it is either found disseminated in the primitive 
rocks, or in alluvial deposits of sand, which appear to have been formed 
by the disintegration of those rocks under the continued action of torrents. 
In the former case, the gold is often found crystallised in cubes and octa- 
hedra, or in forms derived from these, and sometimes aggregated together 
in dendritic or branch-like forms. In the alluvial deposits, the gold is- 
usually found in small scales (gold dust), but sometimes in masses of con- 
siderable size (nuggets), the rounded appearance of which indicates that 
they have been subjected to attrition. 

The extraction of the particles of gold from the alluvial sands is effected 
by taking advantage of the high specific gravity of the metal (19*3) which 
causes it to remain behind, whilst the sand, which is very much lighter 
(sp. gr. 2 -6), is carried away by water. This washing is commonly per- 
formed by hand, in wooden or metal bowls, in which the sand is shaken 
up with water, and the lighter portions dexterously poured off, so as to 
leave the grains of gold at the bottom of the vessel. On a somewhat 
larger scale, the auriferous sand is washed in a cradle or inclined wooden 
trough, furnished with rockers, and with an opening at the lower end for 
the escape of the water. The sand is thrown on to a grating at the head 
of the cradle, which retains the large pebbles, whilst the sand and gold 
pass through, the former being washed away by a. stream of water which 
is kept flowing through the trough. 

When the gold is disseminated through masses of quartz or other rock, 
much labour is expended in crushing the latter before the gold can be 



SMELTING OF GOLD OKES. 401 

separated. This is effected either by passing the coarse fragments between 
heavy rollers of hard cast-iron, or by stamping them, with wooden beams 
shod with iron, in troughs through which water is kept continually 
flowing. 

In some cases it is found advantageous to smelt the ore by fusing it 
with some substance capable of uniting with the gold, and of being after- 
wards readily separated from it. Lead is peculiarly adapted for this 
purpose ; the crushed ore, being mixed with a suitable proportion, either 
of metallic lead, or of litharge (oxide of lead) and charcoal, or even of 
galena (sulphide of lead), together with some lime and oxide of iron or clay, 
to flux the silica, is fused on the hearth of a reverberatory furnace, when 
the fused lead dissolves the particles of gold, and collects beneath the 
lighter slag. The lead is afterwards separated from the gold by cupel] ation 
(see page 370). 

In smelting the ores of gold in Hungary, the metal is concentrated by 
means of sulphide of iron. The ore consists of quartz and iron 'pyrites 
(disulphide of iron), containing a little gold. On fusing the crushed ore 
with lime, to flux the quartz, the pyrites loses half its sulphur, and 
becomes ferrous sulphide (FeS), which fuses and sinks below the slag, 
carrying with it the whole of the gold. If this product be roasted so as to 
convert the iron into oxide, and be then again fused with a fresh portion 
of the ore, the oxide of iron will flux the quartz, whilst the fresh portion 
of sulphide of iron will carry down the whole of the gold contained in 
both quantities of ore. This operation having been repeated until the 
sulphide of iron is rich in gold, it is fused with a certain quantity of lead, 
which extracts the gold and falls to the bottom. The lead is then cupelled 
in order to obtain the gold. 

When the ores of lead, silver, or copper contain gold, it is always found 
to have accompanied the silver extracted from them, and is separated from 
it by a process to be presently noticed. 

Gold is sometimes separated from the impurities remaining with it after 
extraction by washing, by the process of amalgamation., w T hich consists in 
shaking the mixture with mercury in order to dissolve the gold-dust, and 
straining the liquid amalgam through chamois leather, which allows the 
excess of mercury to pass through, but retains the solid portion contain- 
ing the gold, from which the mercury is then separated by distillation.* 

In the Tyrol, this process is adopted for separating the gold from an 
auriferous iron pyrites, by grinding it in a mill of peculiar construction, 
with water and a little mercury, the latter being allowed to act upon suc- 
cessive portions of ore until it becomes sufficiently rich to be strained and 
distilled. 

Gold, as found in nature, is generally alloyed with variable proportions' 
of silver and copper, the separation of which is the object of the gold 
refiner. It may be effected by means of nitric acid, which will dissolve 
the silver and copper, provided that they do not bear too small a propor- 
tion to the gold. Sulphuric acid, however, being very much cheaper, is 
generally employed. The alloy is fused and poured into water, so as to 
granulate it and expose a larger surface to the action of the acid ; it is 
then boiled with concentrated sulphuric acid (oil of vitriol), which con- 

* A small quantity of sodium dissolved in the mercury has been found very materially 
to facilitate the amalgamation of gold and silver Ores, apparently because the amalgam 
of sodium is more highly electro-positive than mercury, in relation* to the gold. 

2 c 



402 REFINING GOLD. 

verts the silver and the copper into sulphates, with evolution of sulphur- 
ous acid gas, whilst the gold is left untouched. In order to recover the 
silver from the solution of the sulphates in water, scraps of copper are 
introduced into it, when that metal decomposes the sulphate of silver, 
producing sulphate of copper, and causing the deposition of the silver 
in the metallic state. 

Finally, the sulphate of copper may he obtained from the solution by 
evaporation and crystallisation. This process is so effectual when the 
proportion of gold in an alloy is very small, that even -^th part of this 
metal may he profitably extracted from 100 parts of an alloy, and much 
gold has been obtained in this way from old silver plate, coins, &c, which 
were manufactured before so perfect a process for the separation of these 
metals was known. On boiling old silver coins or ornaments with nitric 
acid, they are generally found to yield a minute proportion of gold in the 
form of a purple powder. But this plan of separation is not so successful 
when the alloy contains a very large quantity of gold, for the latter metal 
seems to protect the copper and silver from the solvent action of the acid. 
Thus, if the alloy contains more than ^th of its weight of gold, it .is 
customary to fuse it with a quantity of silver, so as to reduce the propor- 
tion of gold below that point before boiling it with the acid. Again, if 
the alloy contains a large quantity of copper, it is found expedient to 
remove a great deal of this metal in the form of oxide by heating the alloy 
in a current of air. 

Gold which is brittle and unfit for coining, in consequence of the pre- 
sence of small quantities of foreign metals, is sometimes refined by melt- 
ing it with oxide of copper or with a mixture of nitre and borax, when 
the foreign metals, with the exception of silver, are oxidised and dissolved 
in the slag. Another process consists in throwing some corrosive sub- 
limate (mercuric chloride) into the melting pot, and stirring it up with 
the metal, w T hen its vapour converts the metallic impurities into chlorides, 
which are volatilised. An excellent method, devised by F. B. Miller of 
Sydney, consists in fusing the gold with a little borax, and passing chlo- 
rine gas into it through a clay tube. Antimony, arsenic, &c, are carried 
off as chlorides, whilst the silver, also converted into chloride, rises to the 
surface of the gold in a fused state, afterwards solidifying into a cake, 
which is reduced to the metallic state by placing it between plates of 
wrought-iron and immersing it in diluted sulphuric acid. 

Pure gold, like pure silver, is too soft to resist the wear to which it is 
subjected in its ordinary uses, and it is therefore alloyed for coinage in 
this country with -^th of its weight of copper, so that gold coin contains 
1 part of copper and 11 parts of gold. The gold used for articles of 
jewellery is alloyed wdth variable proportions of copper and silver. The 
alloy of copper and gold is much redder than pure gold. 

The degree of purity of gold is generally expressed by quoting it as of 
so many carats fine. Thus, pure gold is said to be 24 carats fine ; English 
standard gold 22 carats fine, that is, contains 22 carats of gold out of the 
24. Gold of 18 carats fine would contain 18 parts of gold out of the 24, 
or f ths of its weight of gold. 

Pure gold is easily prepared from standard or jeweller's gold, by dissolving it in 
hydrochloric acid mixed with one-fourth of its volume of nitric acid, evaporating the 
solution to a small bulk to expel excess of acid, diluting with a considerable quantity 
of water, filtering from the separated silver chloride, and adding a solution of green 



PHYSICAL CHAEACTERS OF GOLD. 403 

sulphate of iron, when the gold is precipitated as a dark purple powder, which may- 
be collected on a filter, well washed, dried, and fused in a small French clay crucible 
with a little borax, the crucible having been previously dipped in a hot saturated 
solution of borax, and dried, to prevent adhesion of the globules of gold. The action 
of the ferrous sulphate upon the trichloride of gold is explained by the equation ; 
2AuCl 3 + 6Fe. 2 S0 4 = Au 2 + Fe 2 Cl 6 + 2Fe 2 (S0 4 ) 3 . 

By employing oxalic acid instead of ferrous sulphate, and heating the solution, the 
gold is precipitated in a spongy state, and becomes a coherent lustrous mass under 
pressure. The metal is employed in this form by dentists. 

When standard gold is being dissolved in aqua regia, it sometimes becomes coated 
with a film of silver chloride which stops the action of the acid ; the liquid must 
then be poured off, the metal washed, and treated with ammonia, which dissolves 
the silver chloride; the ammonia must then be washed away before the metal is 
replaced in the acid. In the case of jeweller's gold, it is advisable to extract as much 
silver and copper as possible by boiling it with nitric acid, before attempting to dis- 
solve the gold. Gold lace should be incinerated to get rid of the cotton before being 
treated with acid. 

The genuineness of gold trinkets, &c, is generally tested by touching them with 
nitric acid, which attacks them if they contain a very considerable proportion of 
copper, producing a green stain, but this test is evidently useless if the surface be 
gilt. The weight is, of course, a good criterion in practised hands, but even these 
have been deceived by bars of platinum covered with gold. The specific gravity may 
be taken in doubtful cases ; that of sovereign gold is 17 '157. 

In assaying gold, the metal is wrapped in a piece of thin paper together with about 
three times its weight of pure silver, and added to twelve times its weight of pure 
lead fused in a bone-ash cupel (see page 372) placed in a muffle (or exposed to a 
strong oxidising blowpipe flame), when the lead and copper are oxidised, and the 
fused oxide of lead dissolves that of copper, both being absorbed by the cupel. 
When the metallic button no longer diminishes in size, it is allowed to cool, hammered 
into a flat disk which is annealed by being heated to reduess, and rolled out to a 
thin plate, so that it may be rolled up by the thumb and finger into a comette, which 
is boiled with nitric acid (sp. gr. 1 - 18) to extract the silver ; the remaining gold is 
washed with distilled water, and boiled with nitric acid of sp. gr. 1'28, to extract the 
last traces of silver, after which it is again washed, heated to redness in a small 
crucible, and weighed. 

The stronger nitric acid could not be used at first, since it would be likely to break 
the cornet into fragments which could not be so readily washed without loss. The 
addition of the three parts of silver {quartation) is made in order to divide the alloy, 
and permit the easy extraction of the silver by nitric acid, which cannot be effected 
when the gold predominates. 

303. The physical characters of gold render it very conspicuous among 
the metals; it is the heaviest of the metals in common use, with the 
exception of platinum, its specific gravity being 19 '3. In malleability 
and ductility it surpasses all other metals ; the former property is turned 
to advantage for the manufacture of gold leaf, for which purpose a bar of 
gold is passed between rollers which extend it into the form of a riband ; 
this is cut up into squares, which are packed between layers of fine 
vellum, and beaten with a heavy hammer ; these thinner squares are then 
again cut up and beaten between layers of gold-beater's skin until they 
are sufficiently thin. An ounce of gold may be thus spread over 100 
square feet ; 282,000 of such leaves placed upon each other form a pile of 
only 1 inch high. These leaves will allow light to pass through them, 
and always appear green or blue when held up to the light, though they 
exhibit the ordinary colour of gold by reflected light ; extremely thin 
leaves of gold, obtained by partially dissolving ordinary gold leaf by 
floating it on solution of potassium cyanide, transmit a violet or a red 
light, according to their thickness, though they still appear yellow by 
reflected light, and if taken up on a glass plate and heated to about 600° 
F. they lose their gold reflection and become ruby-red, changing to green 



404 ' OXIDES OF GOLD. 

if pressed with a hard substance. If very finely-divided gold be sus-.' 
pended in water, it imparts a violet or red colour to it. Such coloured; 
fluids containing very minute particles of gold in a state of suspension, 
may be obtained by the action of phosphorus dissolved in ether upon a. 
very weak solution of gold in aqua regia ; on standing for a long time, 
the particles of finely-divided gold are deposited, having the same tint as 
that which they previously exhibited when suspended in the liquid ; the 
blue particles being less minute are soonest deposited, but the red particles 
require many months to settle down. These colours of finely-divided 
gold are taken advantage of in painting upon porcelain, and the well- 
known magnificent ruby-red glass owes its colour to the same cause. 
T ^yth of a grain of gold is capable of imparting a deep rose colour to a 
cubic inch of fluid. 

The extreme ductility of gold is exemplified in the manufacture of gold 
thread for embroidery, in which a cylinder of silver having been covered 
with gold leaf, it is drawn through a wire-drawing plate and reduced to 
the thinness of a hair; in this way 6 ounces of gold are drawn into a 
cylinder two hundred miles in length. Although fusing at about the 
same temperature as copper, gold- is seldom cast, on account of its great 
contraction during solidification. 

Gold is not even affected to the same extent as silver by exposure to 
the atmosphere, for sulphuretted hydrogen has no action upon it, and 
hence no metal is so well adapted for coating surfaces which are required 
to preserve their lustre. 

The gold is sometimes applied to the surfaces of metals in the form of 
an amalgam, the mercury being afterwards driven off by heat. Metals 
may also be gilt by means of a boiling solution prepared by dissolving 
gold in aqua regia, and adding an excess of bicarbonate of potash or of 
soda. But the most elegant process of gilding is that of electro-gilding, 
in which the object to be gilt is connected by a wire with the zinc end 
of the galvanic battery, and immersed in a solution of cyanide of gold in 
cyanide of potassium, in which is also placed a gold plate connected with 
the copper end of the battery, and intended, by gradually dissolving, to 
replace the gold abstracted from the solution at the negative pole. 

A gold crucible is very useful in the laboratory for effecting the fusion 
of substances "with caustic alkalies, which would corrode a platinum 
crucible. 

304. Oxides of gold. — Two compounds of gold with oxygen have been 
obtained, Au 2 and Au 2 3 , but neither of them is of any great practical 
importance. 

• Sesquioxide of gold or auric anhydride (Au 2 3 ) is prepared from the 
solution of gold in aqua regia, by boiling it with excess of potash, decom- 
posing the potassium aurate with sulphuric acid, and purifying the auric 
anhydride by dissolving it in nitric acid and precipitating by water. It 
forms a yellow precipitate, which is easily decomposed by exposure to 
light or to a temperature of 500° F. By dissolving it in potash and 
evaporating in vacuo, the potassium aurate is obtained in yellow needles 
(KAu0 2 3Aq.). Suboxide of gold (Au 2 0) forms a dark precipitate when 
protochloride of gold is decomposed by potash. 

The chlorides of gold correspond in composition to the oxides. The 
trichloride of gold or auric chloride (AuCl y ) is obtained by dissolving 



CHLORIDES OF GOLD. 405 

gold in hydrochloric acid with one-fourth of its volume of nitric acid, 
:and evaporating on a water-bath to a small bulk ; on cooling, yellow pris- 
matic crystals of a compound of the trichloride with hydrochloric #cid 
(AuCl3.HCl.6Aq.) are deposited, from which the hydrochloric acid may- 
be expelled by a gentle heat (not exceeding 250° F.), when the trichloride 
.forms a red-brown deliquescent mass, dissolving very readily in water, 
giving a bright yellow solution which stains the skin and other organic 
matter purple when exposed to light, depositing finely-divided gold. 
Almost every substance capable of combining with oxygen reduces the 
gold to the metallic state. The inside of a perfectly clean flask or tube 
may be covered with a film of metallic gold by a dilute solution of the 
trichloride mixed with citric acid and ammouia, and gently heated. The 
facility with which it deposits metallic gold, and the resistance of the 
deposited metal to atmospheric action, has renlered trichloride of gold 
very useful in photography. Alcohol and ether readily dissolve the tri- 
chloride, the latter being able to extract it from its aqueous solution. 
Red crystals of trichloride of gold are sublimed when thin gold foil is 
gently heated in a current of chlorine. Trichloride of gold (like 
platinic chloride) forms crystal Usable compounds with the alkaline 
chlorides and with the hydrochlorates of organic bases, and affords great 
help to the chemist in detiuing these last. Aurocliloride of sodium forms 
reddish-yellow prismatic crystals (NaCl. AuCl 3 ,4Aq.), which are sometimes 
sold f >r photographic purposes. 

Protochloride of gold or aurous chloride (AuCl) is obtained by gently 
heating the trichloride, when it fuses and is decomposed at 350° F., 
leaving the protochloride, which is reduced to metallic gold at about 400° 
F. The protochloride is sparingly soluble in water and of a pale yellow 
colour. Boiling water decomposes it into metallic gold and the tri- 
chloride. 

Fulminating gold is obtained as a buff precipitate when ammonia is 
added to solution of auric chloride : its composition is not well established, 
but appears to be Au 2 3 .4NH 3 .H 2 0. It explodes violently when gently 
heated. 

The Sel d'or of the photographer is a hyposulphite (thiosulphate) of gold 
and sodium, Au 2 S 2 3 ,3Na 2 S 2 3 ,4Aq., which is obtained in fine white 
needles by pouring a solution of 1 part of auric chloride into a solution of 
3 parts of sodium hyposulphite, and adding alcohol, in which the double 
salt is insoluble. Its formation mav be explained by the equation, 
8Na 2 S 2 3 + 2AuCl 3 = Au 2 S 2 3 , 3Na 2 S 2 3 + 6NaCl + 2Na 2 S 4 6; It is 
doubtful whether the above formula represents the true constitution of 
this silt, for it is not decomposed by acids in the same manner as ordi- 
nary hyposulphites. Nitric acid causes the whole of the gold to separate 
in the metallic state. 

Purple of Casdus, which is employed for imparting a rich red colour to 
glass and porcelain, is a compound of gold, tin, and oxygen, which are be- 
lieved to be grouped according to the formula Au. 2 O.Sn0 2 ,SnO.Sn0 2 .4Aq.* 
It may be prepared by adding stannous chloiide to a mixture of stannic 
chloride and auric chloride; 7 parts of gold are dissolved in aqua regia 
and mixed with 2 parts of tin also dissolved in aqua regia ; this solution 
is largely diluted with water, and a weak solution of 1 part of tin in 

* Debray asserts that it is merely a mixture of precipitated gold and stannic hydrate. 



406 SULPHIDES OF GOLD. 

hydrochloric acid is added, drop by drop, till a fine purple colour is pro- 
duced. The purple of Cassius remains suspended in water in a very fine 
state of division, but subsides gradually, especially if some saline solution 
be added, as a purple powder. The fresh precipitate dissolves in 
ammonia, but the purple solution is decomposed by exposure to light, 
becoming blue, and finally colourless, metallic gold being precipitated, 
and stannic oxide left in solution. 

The sulphides of gold are not thoroughly known. When hydrosul- 
phuric acid acts on solution of auric chloride, a black precipitate of 
Au 2 S,Au 2 S 3 , is obtained, which dissolves in alkaline sulphides. The 
salt Na 2 S,Au 2 S,8Aq. has been obtained, in colourless prisms soluble in 
alcohol. The precipitated sulphide of gold is not dissolved by the acids, 
with the exception of aqua regia. Mtric acid oxidises the sulphur, 
leaving metallic gold. When hydrosulphuric acid is added to a boiling 
solution of auric chloride, the metal itself is precipitated — 

8AuCl 3 + 3H 2 S + -12H 2 = Au 8 + 24HC1 + 3H 2 S0 4 . 

A yellowish-grey brittle arsenide of gold (AuAs 2 ) has been found in 
quartz in Australia, 



OX SOME OF THE 

USEFUL APPLICATIONS ffl CHEMICAL PRINCIPLES 
NAT HITHEBTO MENTIONED 



CHEMICAL PRINCIPLES OF THE MANUFACTURE 

OF GLASS. 

305. Glass is defined chemically to be a mixture of two or more sili- 
cates, one of which is a silicate of an alkali, the other being a silicate of 
lime, baryta, oxide of iron, oxide of lead, or oxide of zinc. 

If silica be fused with an equal weight of carbonate of potash or soda, 
a transparent glassy mass is obtained, but this is slowly dissolved by 
water, and would therefore be incapable of resisting the action of the 
weather: if a small proportion of lime or baryta, or of the oxides of iron, 
lead, or zinc, be added, the glass becomes far less easily affected by atmo- 
spheric influences. 

The most valuable property of glass, after its transparency and per- 
manence, is that of assuming a viscid or plastic consistency when fused, 
which allows it to be so easily fashioned into the various shapes required 
for use or ornament. 

The composition of glass is varied according to the particular purpose 
for which it is intended, the materials selected being fused in large clay 
crucibles placed in reverberator}* furnaces, and heated by a coal lire or in 
a gas-furnace. 

Ordinary window glass is essentially composed of silicate of soda and 
silicate of lime, containing one molecule (13 '3 per cent.; of soda, one 
molecule (12 - 9 per cent.) of lime, and five molecules (69T per cent.) of 
silica- it also usually contains a little alumina. This variety of glass 
is manufactured by fusing 100 parts of sand with about 35 parts oi chalk 
and 35 parts of soda-ash: a considerable quantity of broken window glass 
is always fused up at the same time. Of course, the carbonic acid of the 
chalk and of the carbonate of soda is expelled in the gaseous state; and in 
order that this may not cause the contents of the crucible to froth over 
during the fusion, the materials are first fritted together, as it is termed. 
at a temperature insufficient to liquefy them, when the carbonic acid gas 
is evolved gradually, and the fusion afterwards takes place without 
effervescence. 

Occasionally sulphate of soda is employed instead of the carbonate, 
when it is usual to add a small proportion of charcoal in order to reduce 
the sulphuric to the state of sulphurous oxide, which is far more easily 
expelled. Before the glass is worked into sheets, it is allowed to remain 



408 FLINT GLASS — COLOURED GLASS. 

at rest for some time in the fused state, so that the air-bubbles may 
escape, and the glass-gall or scum (consisting chiefly of sulphate of soda 
and chloride of sodium), which rises to the surface, is removed. 

Plate glass is also chiefly a silicate of soda and lime, but it contains, 
in addition, a considerable quantity of silicate of potash (74 per cent, of 
silicic acid, 12 of soda, 5*5 of potash, and 5*5 of lime). The purest white 
sand is selected, and grpat care is taken to exclude impurities. 

Crown glass, used for optical purposes, contains no soda, since that 
alkali has the property of imparting a greenish tint to glass, which is "not 
the case with potash. This variety of glass, therefore, is prepared by 
fusing sand with carbonate of potash and chalk in such proportions that 
the glass may contain one molecule (22 per cent.) of potash, one molecule 
(12*5 per cent.) of lime, and four molecules (62 per cent.) of silica. 

The glass of which wine bottles are made is of a much cheaper and com- 
moner description, consisting chiefly of silicate of lime, but containing, in 
addition, small quantities of the silicates of the alkalies, of alumina, and 
of oxide of iron, to the last of which it owes its dark colour. It is made 
of the coarsest materials, such as common red sand (containing iron and 
alumina), soap-maker's waste (containing lime and small quantities of 
alkali), lefuse lime from the gas-works, clay, and a very small proportion 
of rock-salt. 

Flint glass, which is used for table glass and for ornamental purposes, 
is a double silicate of potash and oxide of lead, containing one molecule 
(13*67 per cent.) of potash, one molecule (33*28 per cent.) of oxide of 
lead, and six molecules (51*93 per cent.) of silica. It is prepared by 
fusing 300 parts of the purest white sand with 200 parts of minium (red 
oxide of lead), 100 parts of refined pearl-ash, and 30 parts of nitre. The 
fusion is effected in crucibles covered in at the top to prevent the access 
of the flame, which would reduce a portion of the lead to the metallic 
state. The nitre is added in order to oxidise any accidental impurities 
which might reduce the lead. 

The presence of the oxide of lead in glass very much increases its 
fusibility, and renders it much softer, so that it may be more easily cut 
into ornamental forms; it also greatly increases its lustre and beauty. 

Baryta has also the effect of increasing the fusibility of glass, and oxide 
of zinc, like oxide of lead, increases its brilliancy and refracting power, 
on which account it is employed in some kinds of glass for optical purr 
poses. Glass of this description is also made by substituting boracic acid 
for a portion of the silica. 

Some varieties of glass, if heated nearly to their melting-point, and 
allowed to cool slowly, become converted into an opaque very hard mass 
resembling porcelain (Reaumur s porcelain). This change, which is known 
as devitrification, is due to the crystallisation of the silicates contained in 
the mass, and by again fusing it, the glass may be restored to its original 
transparent condition. 

In producing coloured glass, advantage is taken of its property of dis- 
solving many metallic oxides with production of peculiar colours. It has 
been mentioned above that bottle glass owes its green colour to the pre- 
sence of oxide of iron; and since this oxide is generally found in small 
quantity in sand, and even in chalk, it occasionally happens that a glass 
which is required to be perfectly colourless turns out to have a slight green 
tinge. In order to remove this, a small quantity of some oxidising agent 



POTTERY AND PORCELAIN. 409 

is usually added, in order to convert the oxide of iron into the sesquioxide, 
which does not impart any colour when present in minute proportion. A 
little nitre,, is sometimes added for this purpose, or some white arsenic, 
which yields its oxygen to the oxide of iron, and escapes in the form of 
vapour of arsenic; red oxide of lead (Pb 3 4 ) may also be, employed, and 
is reduced to oxide of lead (PbO), which remains in the glass. Binoxide 
of manganese is often added as an oxidising agent, being reduced to the 
state of oxide of manganese (MnO), which does not colour the glass; but 
care is then taken not to add too much of the binoxide, for a very minute 
quantity of this substance imparts a beautiful amethyst purple colour to 
glass. 

Suboxide of copper is used to produce a red glass, and the finest ruby 
glass is obtained, as already mentioned at page 404, by the addition of a 
little gold. The oxides of antimony impart a yellow colour to glass; a 
peculiar brown-yellow shade is given by charcoal in a fine state of division, 
and sesquioxide of uranium produces a tine greenish-yellow glass. Green 
glass is coloured either by oxide of copper or sesquioxide of chromium, 
whilst oxide of cobalt gives a magnificent blue colour. For black glass 
a mixture of the oxides of cobalt and manganese is employed. The white 
enamel glass is a flint glass, containing about 10 per cent, of binoxide of 
tin. Bone-ash is also used to impart this appearance to glass. 

CHEMISTRY OF THE MANUFACTURE OF POTTERY 
AND PORCELAIN. 

306. The manufacture of pottery obviously belongs to an earlier period 
of. civilisation than that of glass, since the raw material, clay, would at 
once suggest, by its plastic properties, the possibility of working it into 
useful vessels, and the application of heat would naturally be had lecourse 
to in order to dry and harden it. Indeed, at the first glance, it would 
appear that this manufacture, unlike that of glass, did not involve the 
application of chemical principL-s, but consisted simply in fashioning the 
clay by mere mechanical dexterity into the required form. It i3 found, 
however, at the outset, that the name of day is applied to a large class of 
minerals, differing very considerably in composition, and possessing in 
common the two characteristic features of plasticity and a piedominance 
of silicate of alumina. 

It has alieaily been stated (page 290) that kaolin is a hydrated silicate 
of alumina, and it is from this material that the best variety of porcelain 
is made. This clay is eminently plastic, and can therefore be readily 
moulded, but when baked, it shrinks very much, so that the vessels made 
from it lose their shape and often crack in the kiln. In order to prevent 
this, the clay is mixed with a certain proportion of sand, chalk, bone-ash, 
or heavy-spar; but another difficulty is thus introduced, for these sub- 
stances diminish the tenacity of the clay, and would thus render the 
vessels brittle. A further addition must therefore be made of some sub- 
stance which fuses at the temperature employed in baking the ware, and 
thus serves as a cement to bind the ui. fused particles of ciay, &c, into 
a compact mass. Felspar (silicate of alumina and potash) answers this 
purpose; or carbonate of potash or of soda is sometimes added, to convert 
•a portion of the silica into a fu«ible alkaline silicate. With a mixture of 
clay with sand and felspar (or some substitutes), a vessel may be moulded 



410 SEVRES AND ENGLISH PORCELAIN. 

which will preserve its shape and tenacity when baked, but it will be 
easily pervious to water, and thus quite unlit for ordinary use. It has, there- 
fore, to be waterproofed by the application of some easily fusible material, 
which shall either form a glaze over the surface, or shall become incor- 
porated with the body of the ware, and the vessel is then fit for all its 
uses. Handles and ornaments in relief are moulded separately, and fixed 
on the ware before baking, and coloured designs are transferred from paper 
to the porous ware before glazing. 

The manufacture of Sevres porcelain is one of the most perfect examples 
of this art. The purest materials are selected in the following propor- 
tions: — Kaolin (porcelain chry), 62 parts; chalk, 4 parts; sand, 17 parts; 
felspar, 17 parts. These materials are ground up with water before 
being mixed, and the coarser particles allowed to subside ; the creamy 
fluids containing the finer particles in suspension are then mixed in 
the proper proportions, and allowed to settle ; the paste deposited at the 
bottom is drained, thoroughly kneaded, and stored away for some months 
in a damp place, by which its texture is considerably improved, and any 
organic matter which it contains becomes oxidised and removed ; the 
oxidation being effected partly by the sulphates present, which become 
reduced to sulphides. It is then moulded into the required forms, and 
dried by simple exposure to the air. The vessels are packed in cylindrical 
cases of a very refractory clay, which are arranged in a furnace or^kiin of 
peculiar construction, and very gradually but strongly heated by the 
flame of a wood fire. When sufficiently baked, the biscuit porcelain has 
to be glazed, and great care is taken that the glaze may possess the same 
expansibility by heat as the ware itself, for otherwise it would crack in all 
directions as the glazed ware cooled. The glaze employed at Sevres is a 
mixture of felspar and quartz very finely ground, and suspended in 
water, to which a little vinegar is added to prevent the glaze from subsid- 
ing too rapidly. When the porous ware is dipped into this mixture, it 
absorbs the water, and retains a thin coating of the mixture of quartz and 
felspar upon its surface. It is now baked a second time, when the glaze 
fuses, partly penetrating the ware, partly remaining as a varnish upon the 
surface. 

When the ware is required to have some uniform colour, a mineral 
pigment capable of resisting very high temperatures is mixed with the 
glaze ; but coloured designs are painted upon the ware after glazing, the 
ware being then baked a third time, in order to fix the colours. These 
colours are glasses coloured with metallic oxides, and ground up with oil 
of turpentine, so that they may be painted in the ordinary way upon the 
surface of the ware ; when the latter is again heated in the kiln, the 
coloured glass fuses, and thus contracts a firm adhesion with the ware. 

Gold is applied either in the form of precipitated metallic gold, or of 
fulminating gold, being ground up in either case with oil of turpentine, 
burnt in, and burnished. 

English porcelain is made from Cornish clay mixed with ground flints, 
burnt bones, and sometimes a little carbonate of soda, borax, and binoxide 
of tin, the last improving the colour of the ware. It is glazed with a 
mixture of Cornish stone (consisting of quartz and felspar), flint, chalk, 
borax, and sometimes white lead to increase its fusibility. 

Stone-ware is made from less pure materials, and is covered with a glaze 
of silicate of soda, in a very simple manner, by a process known as salt- 



BUILDING MATERIALS. 41] 

glazing. The ware is coated with a thin film of sand by dipping it in a 
mixture of fine sand and water, and is then intensely heated in a kiln into 
which a quantity of damp salt is presently thrown. The water is decom- 
posed, its hydrogen taking the chlorine of the salt to form hydrochloric 
acid, and its oxygen converting the sodium into soda, which combines with 
the sand to form silicate of soda; this fuses into a glass upon the surface 
of the ware. 

Pipkins, and similar earthenware vessels, are made of common clay 
mixed with a certain proportion of marl and of sand. They are glazed 
with a mixture of 4 or 5 parts of clay with 6 or 7 parts of litharge. The 
colour of this ware is due to the presence of peroxide of iron. 

Bricks and tiles are also made from common clay mixed, if necessary, 
with sand. These are very often grey, or blue, or yellow, before baking, 
and become red under the action of heat, since the iron, which is originally 
present as carbonate (FeC0 3 ), becomes converted into the red peroxide 
(Fe 2 3 ) by the atmospheric oxygen. 

The impure varieties of clay fuse much more easily than pure clay, 
so that, for the manufacture of the refractory bricks for lining furnaces, 
of glass-pots, crucibles for making cast-steel, &c, a pure clay is employed, 
to which a certain quantity of broken pots of the same material is added, 
to prevent the articles from shrinking whilst being dried. 

Dinas firebricks are made from a peculiar siliceous material found in 
the Vale of Neath, and containing alumina with about 98 per cent, of 
silica. The ground rock is mixed with 1 per cent, of lime and a little 
water before moulding. These bricks are expanded by heat, whilst 
ordinary firebricks contract. 

Blue bricks are glazed by sprinkling with iron scurf, a mixture of par- 
ticles of stone and iron produced by the wear of the siliceous grindstones 
employed in griuding gun-barrels, <fec. When the bricks are fired, a glaze 
of silicate of iron is formed upon them. 

CHEMISTRY OF BUILPING MATERIALS. 

307. Chemical principles would lead to the selection of pure silica 
(quartz, rock-crystal) as the most durable of building materials, since it is 
not acted on by any of the substances likely to be present in the atmo- 
sphere ; but even if it could be obtained in sufficiently large inasses for 
the purpose, its great hardness presents an obstacle to its being hewn into 
the required forms. Of the building stones actually employed, granite, 
basalt, and porphyry are the most lasting, on account of their capability 
of resisting for a great length of time the action of water and of atmo- 
spheric carbonic acid; but their hardness makes them so difficult to work, 
as to prevent their employment except for the construction of pavements, 
bridges, &c, where the work is massive and straightforward, and much 
resistance to wear and tear is required. The millstone grit is also a very 
durable stone, consisting chiefly of silica, and employed for the founda- 
tions of houses. Freestone is a term applied to any stone which is soft 
enough to be wrought with hammer and chisel, or cut with a saw ; it 
includes the different varieties of sandstone and limestone. The sand- 
stones consist of grains of sand cemented together by clay or limestone. 
The Yorkshire flags employed for paving are siliceous stones of this 
description. The Craigleilli sandstone, which is one of the freestones 



412 MOKTAK. 

used in London, contains about 98 per cent, of silica, together with some 
carbonate of lime. 

The building stones in most general use are the different varieties of 
carbonate of lime. The durability of these is in proportion to their com- 
pact structure ; thus marble, being the most compact, has been found to 
resist for many centuries the action of the atmosphere, whilst the more 
porous limestones are corroded at the surface in a very short time. Port- 
land stone, of which St. Paul's and Somerset House are built, and Bath 
,sto7ie, are among the most durable of these ; but they are all slowly cor- 
roded by exposure to the atmosphere. The chief cause of this corrosion 
appears to be the mechanical disintegration caused by the expansion, in 
freezing, of the water absorbed in the pores of the stone. In order to 
determine the relative extent to which different stones are liable to be 
disintegrated by frost, a test has been devised, which consists in soaking 
the stone repeatedly in a saturated solution of sulphate of soda and allow- 
ing it to dry, when the cr} 7 stallisation of the salt disintegrates the stone, 
as freezing water would, so that if the particles detached from the surface 
be collected and weighed, a numerical expression for the resistance of the 
material will be obtained. Magnesian limestones (carbonate of lime with 
carbonate of magnesia) are much valued for ornamental architecture, on 
account of the ease with which they may be carved, and are said to be 
more durable in proportion as they approach the composition expressed by 
the formula CaC0 3 .MgC0 3 .* The magnesian limestone from Bolsover 
Moor, of which the Houses of Parliament are built, contains 50 per 
cent, of calcium carbonate, 40 of magnesium carbonate, with some silica 
and alumina. , ■ 

It is probable that a slow corrosion of the surface of limestone is effected 
by the carbonic acid continually deposited in aqueous solution from the 
air; and it is certain that in the atmosphere of towns the limestone is 
attacked by the sulphuric acid which results from the combustion of coal 
and the operations of chemical works. The Houses of Parliament have 
suffered severely, probably from this cause. Many processes have been 
recommended for the preservation of building stones, such as waterproof- 
ing them by the application of oily and resinous substances, and coating or 
impregnating them with solution of soluble glass and similar matteis ; but 
none seems yet to have been thoroughly te>ted by practical experience. 

Purbedk, Ancaster, and Caen stones are well-known limestones employed 
for building. 

The mortar employed for building is composed of 1 part of freshly : 
slaked lime and 2 or 3 parts of sand intimately mixed with enough water 
to form an uniform paste. The hardening of such a comp »sition appears 
to be due, in the hist instance, to the absorption of carbonic aci 1 fiom 
the air, by which a portion of the lime is converted into carbonate, 
and this, uniting with the unaltered hydrate of lime, forms a solid layer 
adhering closely to the two surfaces of brick or si one, which it cements 
together. In the course of time the lime would act upon the silica, pro- 
ducing silicate of lime, and this chemical action would render the adhesion 
more perfect. The chief use of the sand here, as in the manufacture of 
pottery (page 409), is to prevent excessive shrinking during the drying of 
the mortar. 

* Any excess of calcium carbonate above that required l>y this formula may "be dissolved 
out by treating the puwdered magnesian limestone with weak acetic acid. 



NITRE OR SALTPETRE. 41 '6 

1 In construction? which are exposed to the action of water, mortars of 
peculiar composition are employed. These hydraulic mortars, or cements, 
as they are termed, are prepared by calcining mixtures of carbonate of 
lime with from 10 to 30 per cent, of clay, when carbonic acid gas is expelled, 
and the lime combines with a portion of the silica from the clay, producing 
a silicate of lime, and probably also, with the alumina, to form aluminate 
of ]ime. When the calcined mass is ground to powder and mixed with 
water, the silicates of alumina and lime, and the aluminate of lime, unite 
to form hydrated double silicates and aluminates, upon which water has 
no action. Roman cement is prepared by calcining a limestone containing 
about 20 per cent, of clay, and hardens in a very short time after mixing 
with water. 

For Portland cement (so-called from its resembling Portland stone) a 
mixture of river mud (chiefly clay) and limestone is calcined at a very 
high temperature. 

Concrete is a mixture of hydraulic cement with small gravel. A speci- 
men of this material from a very ancient Phoenician temple was as hard 
as rock, and contained nearly 30 per cent, of pebbles. 

Scotfs cement was prepared by passing air containing a small quantity 
of sulphurous acid gas, evolved from burning sulphur, over quicklime 
heated to dull redness. The setting, of this cement appears due to the 
presence of a small proportion of sulphate of lime very intimately mixed 
with the quicklime. The mixture of these substances yields the cement 
by a less circuitous process. 

GUNPOWDER. 

308. Gunpowder is a very intimate mixture of saltpetre (nitre or 
nitrate of potassium), sulphur, and charcoal, which do not act upon each 
other at the ordinary temperature, but when heated together, arrange 
themselves into new forms, evolving a very large amount of gas. 

In order to manufacture gunpowder capable of producing the greatest 
possible effect, great attention is requisite to the purity of the ingredients, 
the process of mixing, and the form ultimately given to the finished 
powder. 

Chemistry of the Ingredients of Gunpowder — Saltpetre. — Nitrate 
x>f potassium (KN0 3 ), nitre or saltpetre, is found in some parts of India, 
especially in Bengal and Oude, where it sometimes appears as a white 
incrustation on the surface of the soil, and is sometimes mixed with 
it to some depth. The nitre is extracted from the earth by treating it 
with water, and the solution is evaporated, at first by the heat of the sun, 
and afterwards by artificial heat, when the impure crystals are obtained, 
which are packed in bags and sent to this country as grough (or impure) 
saltpetre. It contains a quantity of extraneous matter varying from 1 to 
10 per cent., and consisting of the chlorides of potassium and sodium, 
sulphates of potassium, sodium, and calcium^ vegetable matter from the 
-soil, sand, and moisture. The number representing the weight of impurity 
present is usually termed the refraction of the nitre, in allusion to the old 
method of estimating it by casting the melted nitre into a cake and 
examining its fracture, the appearance of which varies according to the 
amount of foreign matter present. 



414 ARTIFICIAL PRODUCTION OF NITRE. 

Peruvian or Chili saltpetre is the nitrate of sodium (NaN0 3 ) found 
in Peru and Chili in beds beneath the surface soil. It is often spoken 
of as cubical saltpetre, since it crystallises in rhombohedra, easily mis- 
taken for cubes, whilst prismatic saltpetre, nitrate of potassium, crystallises 
in six-sided prisms. Nitrate of sodium cannot be substituted for 
nitrate of potassium as an ingredient of gunpowder, since it attracts 
moisture from the air, becoming damp, and appears to be less powerful 
in its oxidising action upon combustible bodies at a high temperature. 
The Peruvian saltpetre, however, forms a very important source 
from which to prepare the nitrate of potassium for gunpowder, since 
it is easily converted into this salt by double decomposition with 
chloride of potassium. The latter salt is now imported in so large a 
quantity from the salt mines of Stassfurth (page 260) that it enables 
nitrate of sodium to be very cheaply converted into nitrate of potassium, 
and renders Indian saltpetre of less importance to the manufacturer of 
gunpoAvder. 

In order to understand the production of saltpetre by the decomposi- 
tion of nitrate ot sodium with chloride of potassium, it is necessary to be 
acquainted with the solubility of those salts and of the salts produced 
by their mutual decomposition. 



100 parts of boiling water dissolve 
218 parts of nitrate of sodium, 

53 ,, chloride of potassium. 
200 ,, nitrate of potassium, 



100 parts of cold water dissolve 
50 parts of nitrate of sodium, 
33 ,^ chloride of potassium, 
30 ,,^ nitrate of potassium, 



37 ,, chloride of sodium. | 36 ,, chloride of sodium. 

It is a general rule that when two salts in solution are mixed, which 
are capable of forming, by exchange of their metals, a salt which is less 
soluble in the liquid, that salt will be produced and separated. 

Thus, when nitrate of sodium and chloride of potassium are mixed, and 
the solution boiled down, chloride of sodium is deposited, and nitrate of 
potassium remains in the boiling liquid, NaN0 3 + KOI = KN0 3 + NaCl. 
When this is allowed to cool, the greater part of the nitrate of potas- 
sium crystallises out, leaving the remainder of the chloride of sodium in 
solution. 

The method usually adopted is to add the chloride of potassium by 
degrees to the boiling solution of nitrate of sodium, to remove the 
chloride of sodium with a perforated ladle in proportion as it is deposited, 
and after allowing the liquid to rest for some time to deposit suspended 
impurities, to run it out into the crystallising pans. 

The potassium-salt required for the conversion of nitrate of sodium 
into nitrate of potassium is sometimes obtained from the refuse of the 
beet-root employed in the the manufacture of sugar. 

Chili saltpetre sometimes contains a considerable proportion of iodate. 
Yellow samples containing chromate are occasionally found. 

Nitrate of potassium is sometimes prepared from the nitrates obtained 
in the nitre-heaps, which consist of accumulations of vegetable and animal 
refuse with limestone, old mortar, ashes, &c. These heaps are constructed 
upon an impermeable clay floor under a shed to protect them from rain. 
One side of the heap is usually vertical and exposed to the prevailing 
wind, the other side being cut into steps or terraces. They are 
occasionally moistened with stable drainings, which are allowed to run 
into orooves cut in the steps at the back of the heap. In such a mass, 



SALTPETRE REFINING. 



415 



at an atmospheric temperature between 60° and 70° F., nitrates of the 
various metals present in the heap are slowly formed, and being dissolved 
by the moisture, are left by it, as it evaporates on the vertical side, in 
the form of an efflorescence. When this has accumulated in sufficient 
quantity, it is scraped off, together with a few inches of the nitrified 
earth, and extracted with water, which dissolves the nitrates, whilst the 
undissolved earth is built up again on the terraced back of the heap. 
After two or three years the heap is entirely broken up and reconstructed. 
The principal nitrates which are found dissolved in water are those of 
potassium, calcium, magnesium, and ammonium, the three last of which 
may be converted into nitrate of potassium by decomposing them with 
carbonate of potassium. 

The formation of nitrates in these heaps probably results from chemical 
changes similar to those which occur in the soils in which nitre is 
naturally formed, but, at present, these changes are not thoroughly 
explained. Some chemists are of opinion that nitrates are formed 
from atmospheric nitrogen and oxygen, encouraged by the presence of 
porous solids, and of matters undergoing oxidation. The explanation 
which is best supported by experimental evidence is that which refers 
their formation to the oxidation of ammonia (page 132), evolved by the 
putrefaction of the nitrogenised matters which the heaps contain, this 
oxidation also being much promoted by the presence of the strongly 
alkaline lime, of the porous materials capable of absorbing ammonia and 
presenting it under circumstances favourable to oxidation, and of a 
peculiar mycoderm or minute fungus (page 134). 

In refining saltpetre for the manufacture of gunpowder, the impure 
(grough) salt is dissolved in about an equal weight of boiling water in a 
copper ooiler, the solution run through cloth niters to remove insoluble 
matter, and allowed to crystallise in a shallow wooden trough lined with 
copper, the bottom of which is formed of two inclined planes (fig. 275). 
Whilst cooling, the solution is kept in continual agitation with wooden 
stirrers, in order that the saltpetre may be deposited in the minute crystals 
known as saltpetre fiour, and not in the large prisms 
which are formed when the solution is allowed to 
crystallise tranquilly, and which contain within them 
cavities enclosing some of the impure liquor from 
which the saltpetre has been crystallised. The salt- 
petre, being so much less soluble in cold than in hot 
water, is, in great part, deposited as the liquid cools, 
whilst the chlorides and other impurities being present 
in small proportion, and not presenting the same 
disparity in their solubility at different temperatures, 
are retained in the liquid. The saltpetre flour is 
drained in a wooden trough with a perforated bottom, 
and transferred to a washing-cistern, where it is 
allowed to remain for half an hour in contact with 
two or three successive small quantities of water, to 
wash away the adhering impure liquor ; it is then allowed to drain 
thoroughly, and in that state, containing from 3 to 6 per cent, of water, 
according to the season, is ready to be transferred to the incorporating mill 
or to a hot-air oven, where it is dried if not required for immediate use. 

The mother liquor, from which the saltpetre flour has been deposited,. 




Fig. 275. 



4.16 PROPERTIES OF SALTPETRE. 

is boiled down and crystallised, the crystals being worked up with the 
next batch of grougli nitre. The final washings of the flour are returned 
to the boiler in which the grough nitre is originally dissolved. When 
the saltpetre contains very much colouring matter, a little glue or animal 
charcoal is employed by the refiner to assist in its removal. 

The impurities most objectionable in the saltpetre employed for gun- 
powder would be the chlorides of potassium and sodium, which cause it 
to absorb moisture easily from the air; the chief test, therefore, to which 
the refiner subjects it, is the addition, to its solution in distilled water, 
of a few drops of solution of nitrate of silver, which causes a milkiness, 
due to the separation of a precipitate of chloride of silver, if the 
chlorides have not been entirely removed. Moreover, the sample should 
dissolve entirely in water, to a perfectly clear colourless solution, which 
should have no effect on blue or red litmus paper, and should give no 
cloudiness with chloride of barium (indicating the presence of sulphates), 
or with oxalate of ammonia (indicating lime), when these are added to 
separate portions of it. Very minute quantities of sulphates and of lime, 
such as may have been derived from the use of river water in washing 
the flour, are generally disregarded. 

Properties of saltpetre. — Nitrate of potassium is usually distinguishable 
by the long striated or grooved six-sided prismatic form in which it 
crystallises (though it may also be obtained in rhombohedral crystals like 
those of nitrate of sodium), and by the deflagration which it produces when 
thrown on red hot coals. It fuses at about 635° F. to a colourless liquid, 
which solidifies on cooling to a translucent brittle crystalline mass. The 
sal pranelle of the shops consists of nitre which has been fused and cast 
into balls. At a red heat it effervesces from the escape of bubbles of 
oxygen, and is converted into nitrite of potassium (KN0 2 ), which is 
itself decomposed by a higher temperature, evolving nitrogen and oxygen, 
and leaving a mixture of potash (K 2 0) and peroxide of potassium 
(K 9 2 ). In contact with any combustible body, it undergoes decom- 
position with great rapidity, five-sixths of its oxygen being available for 
the oxidation of the combustible substance, and the nitrogen being 
evolved in the free state; thus, in contact with carbon, the decomposition 
of the nitre may be represented by the equation — 

2KNO :3 + C3 = K 2 C0 3 + C0 2 + CO + N 2 . 

Since the combustion of a large quantity of material may be thus 
effected in a very small space and in a short time, the temperature pro- 
duced is much higher than that obtained by burning the combustible 
in the ordinary way. The specific gravity of saltpetre is 2 '07, so that 
1 cubic inch weighs 523 grains (obtained by multiplying the weight of 
a cubic inch of water, 252*5 grains, by 2*07). Since 202 grains (2 mole- 
cules) of nitre contain 80 grains (5 atoms) of oxygen available for the 
oxidation of combustible bodies, 523 grains, or 1 cubic inch, of nitre, 
would contain 207 grains or 605 cubic inches of available oxygen, a 
volume which would be contained in about 3000 cubic inches of air ; 
hence, 1 volume of saltpetre represents, in its power of supporting com- 
bustion, 3000 volumes of atmospheric air. It also enables some com- 
bustible substances to burn without actual flame, as is exemplified by its 
use in toudtpaper or slotv port-fire, which consists of paper soaked in a 
weak solution of saltpetre and dried. 



COMPOSITION OF CHARCOAL. 



417 



If a continuous design be traced on foolscap paper with a brush dipped in' a solu- 
tion of 30 grains of saltpetre in 100 grains of water, and allowed to dry, it will be 
found that when one part of the pattern is touched with a red hot iron, it will 
gradually burn its way out, the other portion of the paper remaining unaffected. 

A mixture of 90 grains of saltpetre, 30 of sulphur, and 30 of moderately fine 
sawdust (Baumes Jlux) will deflagrate with sufficient intensity to fuse a small silver 
coin into a globule ; the mixture may be pressed down in a walnut shell or a small 
porcelain crucible, and the coin buried in it, the flame of a lamp being applied out- 
side until deflagration commences. 

Pulvis fulminans is a mixture of 3 parts of saltpetre, 1 part of sulphur, and 2 of 
carbonate of potash, all carefully dried ; when it is heated on an iron plate, no action 
takes place till it melts, when it explodes very violently. 

Charcoal for Gunpowder. — Charcoal has been already described as 
the residue of the destructive distillation of wood, in which, process the 
hydrogen and oxygen of the wood are for the most part expelled in the 
forms of wood naphtha (CH 4 0), pyroligneous acid (C 2 H 4 2 ), carbonic 
acid gas, carbonic oxide, water, &c, leaving a residue containing a much 
larger proportion of carbon than the original wood, and therefore capable 
of producing a much higher temperature (page 69) by its combustion with 
the saltpetre. The higher the temperature to which the charcoal is 
exposed in its preparation, the larger the proportion of hydrogen and 
oxygen expelled, and the more nearly does the charcoal approach in com- 
position to pure carbon ; but it is not found advantageous in practice to 
employ so high a temperature, since it yields a dense charcoal of difficult 
combustibility, and therefore less fitted for the manufacture of powder. 
The average, composition of wood, exclusive of ash, is, in 100 parts — 



Carbon. 
50 



Hydrogen. 



Oxygen. 
44 



The composition of the charcoal prepared at different temperatures is 
given in the following table : — 



Temperature 
of Charring. 


Carbon. 


Hydrogen. 


Oxygen. 


Ash. 


270° C. 
363° 
476° 
519° 


71 
80-1 
85-8 
86-2 


4-6 
3-71 
313 
3-11 


23 

14-55 
9-47 
9-11 


1-4 

1-64 
1-60 

1-58 



The charcoal employed for gunpowder in this country is prepared at 
temperatures between 360° C. and 520° C. It will be seen that the 
proportion of carbon, upon which the heating value of the charcoal 
depends, increases with the final temperature of carbonisation ; but it has 
been found that the rapidity with which the temperature is raised has 
also a great effect in increasing the proportion of carbon, as shown in the 
following table : — 



Final 

Temperature. 


Time of 
Heating. 


Percentage 
of Carbon. 


Final 
Temperature. 

490 °C. 

555° 

558° 


Time of 
Hating. 


Percentage 
of Carbon. 


410° C. 

414° 

490° 


5 hours. 

n „ 

8i » 


81-65 
83-14 
84-19 


2f hours 
3 ,, 


86-34 
83-32 
86-52 



The charcoal prepared between 260° and 320° C. has a brown colour 
{ckarbon roux), and although it is more easily inflamed than the black 
charcoal obtained at higher temperatures, the presence of a large pro- 

2d 



418 



CHARCOAL FOR GUNPOWDER. 



portion of oxygen so much diminishes its calorific value, that its employ- 
ment in gunpowder is not advantageous. It is used on the Continent in 
the manufacture of sporting-powder, and is prepared by exposing the 
wood, in an iron cylinder, to the action of high-pressure steam heated to 
about 280° C. Charcoal prepared at low temperatures gives somewhat 
higher velocities, but absorbs much more moisture' than that prepared at 
high temperatures. 

Light woods, such as alder, willow, and dogwood,* are selected for the 
preparation of charcoal for gunpowder, because they yield a lighter and 
more easily combustible charcoal, dogwood being employed for the best 
quality of powder for small arms. This wood is chiefly imported, since it 
has not been successfully grown in this country. The wood is stripped 
of its bark, and either exposed for a length of time to the air or dried in 
a hot chamber. Considerable loss of charcoal takes place if damp wood 
be charred, a portion of the carbon being oxidised by the steam at a high 
temperature. 

In order to convert the wood into charcoal, 1 \ cwt. of wood is packed 
into a sheet-iron cylinder or slip (fig. 276), one end of which is closed 

by a tightly-fitting cover, and the 
other by a perforated plate, to 
allow of the escape of the gases 
and vapours expelled during the 
carbonisation. This cylinder is 
then introduced into a cylindrical 
cast- iron retort, built into a brick 
furnace, and provided with a pipe 
(L) for the escape of the products, 
which are usually carried back 
into the furnace (B) to be con- 
sumed. The process of charring 
occupies from 2J to 3J hours, and 
as soon as it is completed, which 
is known by the violet tint of the 
(carbonic oxide) flame from the 
pipe leading into the fire, the slip is transferred to an iron box or 
extinguisher, where the charcoal is allowed to cool. About 40 lbs. of 
charcoal are obtained from the above quantity of wood. Charcoal 
prepared by this process is spoken of as cylinder charcoal, to distinguish 
it from pit charcoal, prepared by the ordinary process of charcoal- 
burning described at page 65, and which is employed for fuze com- 
positions, &c, but not for the best gunpowder. The fitness of the 
charcoal for the manufacture of powder is generally judged of by its 
physical characters. It is of course desirable that the charcoal should 
be as free from incombustible matter as possible. The proportion of the 
ash left by different charcoals varies considerably, but it seldom exceeds 
2 per cent. This ash consists chiefly of the carbonates of potassium and 
calcium ; it also contains calcium phosphate, magnesium carbonate, 
silicate and sulphate of potassium, chloride of sodium, and the oxides of 
iron and manganese. 

The charcoal is kept for about a fortnight before being ground, for if 

* Dogwood charcoal is not made from the true dogwood (cornus), but from the alder 
buckthorn (Rhamnus frangula), commonly called black dogwood. 




Fig. 2 



Charcoal retort. 



SULPHUR FOR GUNPOWDER. 419 

ground when fresh, before ifc has absorbed moisture and oxygen from the 
air, it is liable to spontaneous combustion. The grinding is effected in a 
mill resembling a cotfee-mill, and the charcoal is afterwards sifted. 

The properties of charcoal have been already described ; its great ten- 
dency to absorb moisture from the air is of some importance in the manu- 
facture of gunpowder, from its causing a false estimate to be made of the 
proportion employed, unless the actual amount of water present in the 
charcoal is known. 

Tar charcoal is the name given to sticks of charcoal which have acci- 
dentally become coated with a shining film of carbon left behind by tar 
which has condensed upon it in the retorts ; it is sometimes rejected by 
the powder manufacturer. 

Sulphur for Gunpowder. — Distilled sulphur (page 188) is the variety 
always employed for the manufacture of gunpowder, the sublimed sulphur 
being employed for fuze compositions, &q. The alleged reason for the 
preference is that the sublimed sulphur, having been deposited in a 
chamber containing much sulphurous and sulphuric acid vapours,* its 
pores have become charged with acid which would be injurious in the 
powder; but it has been pointed out (page 191) that distilled sulphur 
consists entirely of the soluble or electro-negative variety of sulphur, 
whilst sublimed sulphur contains a large proportion of the insoluble or 
positive sulphur, which would probably influence its action in gunpowder. 
The sulphur should leave scarcely a trace of incombustible matter when 
burnt, and after stirring the powdered sulphur for some time with warm 
distilled water, the latter should only very feebly redden blue litmus. 
As an ingredient of gunpowder, sulphur is valuable on account of the 
low temperature (500° F.) at which it inflames, thus facilitating the 
ignition of the powder. Its oxidation by saltpetre appears also to be 
attended with the production of a higher temperature than is obtained 
with charcoal, which would have the effect of accelerating the combustion 
and of increasing, by expansion, the volume of gas evolved. The sulphur 
is ground under edge-runners (fig. 277) and sifted. 

The difference in the inflammability of sulphur and charcoal is strikingly shown 
by heating a square of coarse wire-gauze over a flame till it is red hot in the centre, 
placing it over a jar of oxygen, allowing it to cool till it no longer kindles charcoal- 
powder sprinkled through it from a pepper-box, and whilst the cloud of charcoal is 
still floating in the gas, throwing in sulphur from a second box ; the hot gauze will 
inflame the sulphur, and this will kindle the charcoal. 

An iron rod allowed to cool below redness may be used to stir a mixture of charcoal 
with (3 parts of) nitre ; but if dipped into powdered sulphur, at once inflames it, 
and the flame of the sulphur will kindle the mixture. The effect of the same rod 
upon mixtures of nitre with charcoal alone, and with charcoal and sulphur, is 
instructive. 

The acceleration of the combustion of gunpowder by the sulphur is well shown by 
laying a train, of which one-half consists of a mixture of 75 nitre and 25 charcoal, 
and the other of 75 nitre, 15 charcoal, and 10 sulphur, a red hot iron being applied 
at the junction of the two trains to start them together. 

Manufacture op Gunpowder. — The proportions of the ingredients of 
gunpowder have been varied somewhat in different countries, the saltpetre 
ranging from 74 to 77 per cent., the charcoal from 12 to 16 per cent., and 
the sulphur from 9 to 12 -5 per cent. English Government powder contains 
75 per cent, of nitre, 15 per cent, of charcoal, and 10 per cent, of sulphur. 

* For certain compositions in which sublimed sulphur is used, it is well washed with 
water in order to remove the acid from its pores. 



420 



MANUFACTURE OF GUNPOWDER. 




Fig. 277. — Incorporating mill. 



An extra pound of saltpetre is generally added at Waltham, to compen- 
sate for loss in manufacture. 

The powdered ingredients* are first roughly mixed in a revolving gun- 
metal drum, with mixing arms turning in an opposite direction, and the 
mixture is subjected, in quantities of about 50 lbs. at a time, to the action 
of the incorporating mill (fig. 277), where it is sprinkled with water, 

poured through the funnel (F), or 
from a can with a fine rose, and 
exposed to trituration and pressure 
under two cast-iron edge-runners (B), 
rolling round in different paths upon 
a cast-iron bed, a ' very intimate 
mixture being thus effected by the 
same kind of movement as in a 
common pestle and mortar, the distri- 
bution of the nitre through the mass 
being also assisted by its solubility in 
water. A wooden scraper (C) tipped 
with copper prevents the roller from 
getting clogged, and a plough (D) 
keeps the mixture in the path. Of 
course, the water employed to moisten 
the powder must be as free from deliquescent salts (especially chlorides, see 
page 416) as possible; at Waltham condensed steam is employed : the 
quantity required varies with the state of the atmosphere. The duration 
of the incorporating process is varied according to the kind of. powder 
required, the slow-burning powder employed for cannon being sufficiently 
incorporated in about three hours, whilst rifle-powder requires five hours. 

The dark grey mass of mill-cake which is thus produced, contains 2 or 
3 per cent, of water. It is broken up by passing between grooved rollers 
of gun metal, and is then placed, in layers of about half an inch thick, 
between copper plates packed in a stout gun-metal box lined inside and 
outside with wood, in which it is subjected for a quarter of an hour to a 
pressure of about 70 tons on the square foot, in a hydraulic press, which 
has the effect of condensing a larger quantity of explosive material into a 
given volume, and of diminishing the tendency of the powder to absorb 
moisture from the air and to disintegrate or dust after granulation. The 
press-cake thus obtained is very hard and compact, resembling slate in 
appearance. As far as its chemical nature is concerned, it is finished 
gunpowder, but if it be reduced to powder and a gun loaded with it, the 
combustion of the charge is found to take place too slowly to produce its 
full effect, since the pulverulent form offers so great an obstacle to the 
passage of the flame by which the combustion is communicated from one 
end of the charge to the other. The press-cake must, therefore, be 
granulated (corned) or broken up into grains of sufficient size to allow the 
rapid passage of the flame between them, and the consequent immediate 
firing of the whole charge. The granulation is effected by crushing the 
press-cake between successive pairs of toothed gun-metal rollers, from 
which it falls on to sieves, which separate it into grains of different sizes, 
the dust, or meal powder, passing through the last sieve. At Waltham, 

* The amount of water in the moist saltpetre (page 415) is ascertained by drying and 
melting a weighed sample before the proportions are weighed out. 



PROPERTIES OF GUNPOWDER. 421 

the R.L.G. (rifle large grain) passes through a sieve of 4 meshes to the 
inch, and is retained on one of 8 meshes, whilst R.F.G. (rifle fine grain) 
passes through a 12-mesh, and is retained on a 20-mesh sieve. The 
granulated powders are freed from dust by passing them through revolv- 
ing cylinders of wooden framework covered with canvas or wire cloth, 
and the fine grain powder is glazed by the friction of its own grains 
against each other in revolving barrels. The large-grain powders are 
sometimes glazed or faced with graphite, by introducing a little of that 
substance into the glazing-barrels with the powder. The powder is 
dried in a chamber heated by steam, very gradually, so as not to injure 
the grain, and is once more dusted in canvas cylinders before being packed. 

For very large charges, the grains having a diameter of \ to \ inch 
(R.L.G.) are found to burn too rapidly, exerting too great a strain upon 
the gun. In such cases, pebble powder, the grains of which vary from 
|- to 1|- inch or more in diameter, is employed. 

Prismatic powder consists of large grains made of a regular six-sided 
prismatic form by compressing the powder-meal (without previously 
making it into press-cake) in moulds, with metal punches, whereas, the 
pebble powder is irregular in form. The prismatic powder is made with 
perforations in the direction of its length to facilitate the passage of flame 
through the charge. 

Pellet powder is moulded in a similar manner into cylindrical pellets 
about J inch long and f inch in diameter, perforated at one end to about 
the centre. 

309. Properties of Gunpowder. — Good gunpowder is composed of 
hard angular grains, which do not soil the fingers, and have a perfectly 
uniform dark grey colour. Its specific gravity {absolute density) as deter- 
mined by the densimeter* varies between 1 *67 and 1'84, and its apparent 
density (obtained by weighing a given measure of the grain against an 
equal measure of water) varies from 0'89 to 0-94, so that a cubic foot 
will weigh from 55 to 58 lbs. When exposed to air of average dryness, 
gunpowder absorbs from 0*5 to 1*0 per cent, of water. In damp air it 
absorbs a much larger proportion, and becomes deteriorated in conse- 
quence of the saltpetre being dissolved, and crystallising upon the surface 
of the grains. Actual contact with water dissolves the saltpetre and 
disintegrates the grains. When very gradually heated in air, gunpowder 
begins to lose sulphur, even at 212° F., this ingredient passing off rapidly 
as the temperature rises, so that the greater part of it may be expelled 
without inflaming the powder, especially if the powder is heated in 
carbonic acid gas or hydrogen, to prevent contact with air. If gunpowder 
be suddenly heated to 600° F. in air, it explodes, the sulphur probably 
inflaming first ; but out of contact with air a higher temperature is 
required to inflame it. The ignition of gunpowder by flame is not 
ensured unless the flame be flashed among the grains of powder ; it often 
takes some time to ignite powder with the flame of a piece of burning 
paper or stick, but contact with a red hot solid body inflames it at once. 
A heap of good powder, when fired on a sheet of white paper, burns with- 
out sparks and without scorching or kindling the paper, which should 
exhibit only scanty black marks of charcoal after the explosion. If the 

* This is a simple apparatus for determining the weight of mercury displaced by a given 
weight of gunpowder, from which all the air Las been exhausted. 



42 2 PEODUCTS OF EXPLOSION OF GUNPOWDER. 

powder has not "been thoroughly incorporated, it will leave minute 
globules of fused nitre upon the paper. Two ounces of the powder should 
be capable of throwing a 68-lb. shot to a distance of 260 to 300 feet from 
an 8-inch mortar at 45° elevation. 

This mode of testing power by the eprouvette mortar is not now 
applied to Government powders. Tar more accurate results are obtained 
by measuring the velocity imparted to a projectile of known weight by a 
given chai'ge of the powder. The velocity is measured by means of a 
clironosco}ie which registers the distance travelled by the shot in a given 
time by causing it to cut the wire of one electrical circuit at the com- 
mencement of its flight, and that of another at the conclusion, thus 
telegraphing its velocity to the instrument room at a distance. 

Cannon powder (R.L.G.) is tested by firing a charge of 1 lb. from a 
muzzle-loader rifled gun, with a 12-lb shot. Small arm powder (R.F.G.) 
is fired from a Snider-Enfield or Martini-Henry rifle. The mean velocity 
at a distance of 105 feet from the muzzle is determined. For R.L.G. 
it amounts to about 1000 feet per second. A charge of 70 grs. of R.F.G. 
in the Snider-Enfield rifle gives a velocity somewhat greater than this. 

Very fortunately, it is difficult to explode gunpower by concussion, 
though it has been found possible to do so, especially on iron, and acci- 
dents appear to have been caused in this way by the iron edge-runners in 
the incorporating mill, when the workmen have neglected the special 
precautions which are laid down for them. The use of stone upon iron 
in the incorporation is avoided, because of the great risk of producing 
sparks, and copper is employed in the various fittings of a powder mill 
wherever it is possible. 

The electric spark is, of course, capable of firing gunpowder, though 
it is not easy to ensure the inflammation of a charge by a spark unless its 
conducting powder is slightly improved by keeping it a little moist, which 
may be effected by introducing a minute quantity of chloride of calcium. 

310. Products of Explosion of Gunpowder. — In the explosion of 
gunpowder, the oxygen of the nitre converts the carbon of the charcoal 
chiefly into carbonic acid gas (C0 2 ), part of which assumes the gaseous' 
state, whilst the remainder is converted into potassium carbonate (K 2 C0 3 ). 
The greater part of the sulphur is converted into potassium sulphate 
(K 2 S0 4 ). The chief part of the nitrogen contained in the nitre is 
evolved in the uncombined state. The rough chemical account of the 
explosion of gunpowder, therefore, is that the mixture of nitre, sulphur, 
and charcoal is resolved into a mixture of potassium carbonate, potassium 
sulphate, carbonic acid gas, and nitrogen, the two- last being gases, the 
elastic force of which, when expanded by the heat of the combustion, 
accounts for the mechanical effect of the explosion. 

But in addition to these, several other substances are found among the 
products of the explosion. Thus, the presence of potassium sulphide 
(K 2 S) may be recognised by the smell of hydric sulphide produced 
on moistening the solid residue in the barrel of a gun, and hydric sulphide 
(H 2 S) itself may often be perceived in the gases produced by the explosion, 
the hydrogen being derived from the charcoal. A little marsh gas 
(CH 4 ) is also found among the gases, being produced by the decomposition 
of the charcoal, a portion of the hydrogen of which is also disengaged 
in the free state. Carbonic oxide (CO) is always detected among the 



PRODUCTS OF EXPLOSION OF GUNPOWDER. 



423 



products. It is evident that the collection for analysis of the products of 
explosion must be attended with some trouble, and that considerable 
differences are to be expected between the results obtained by different 
operators, from the variation of the circumstances under which the powder 
is tired and the products collected. When the powder is slowly fired, 
a considerable proportion of the nitrogen in the saltpetre is evolved in 
the form of nitric oxide gas (NO), which is not found among the 
products of the rapid explosion of powder. 

Some of the most recent experiments upon the explosion of gunpowder 
have been made by Noble and Abel under conditions very similar to 
those which occur in practice, the powder having been confined in a strong 
vessel of mild steel, in which the powder was tired by electricity, so that 
the gaseous and solid products of the explosion remained within the 
vessel, and could be submitted to analysis. 

Three samples of powder manufactured at Waltham Abbey were thus 
examined. Their composition is stated in the following table : — 





Pebble 
Powder. 


Rifle 
Large Grain. 


Fine Grain. 


Nitre .... 

Sulphur, .... 

Charcoal, viz., Carbon, . 
Hydrogen, 
Oxygen, 
Ash, 

Water, . 

Sulphate of potassium, . 


74-67 
10-07 
12-12 
0-42 
1-45 
0-23 
0-95 
0-09 


74-95 
10-27 
10-86 
0-42 
1-99 
0-25 
1-11 
0-15 


73-55 

10-02 

11-36 

0-49 

2-57 
0-17 
1-48 
0-36 


100-00 


.100-00 


100-00 



The quantities of gunpowder exploded in different experiments varied 
from 3 J oz. to 1 lb. 10 oz., and the pressures observed varied from 1 ton 
to over 36 tons on the square inch. 

The solid products were found almost entirely collected at the bottom 
of the vessel, forming an exceedingly hard mass of a dark olive-green 
colour, exceedingly deliquescent, smelling strongly of hydric sulphide, 
and frequently also of ammonia. In some instances the solid residue 
was observed to become heated by exposure to air, from the rapid absorp- 
tion of oxygen. 

The following table shows the proportions of solid and gaseous products 
furnished by each powder, when the ratio between the volume of the 
charge and that of the containing space was varied so that the maximum 
pressures attained were those stated at the head of each column : — 





Pebble Powder. 


Rifle Large Grain. 


Fine Grain. 


Pressure, in tons per. sq. inch, 
Weight of solid products from ) 

100 parts powder, . . \ 
Weight of gaseous products ) 

from 100 parts powder, . \ 


1-4 
56-12 

43-88 


12-5 

55-17 

44-83 


1-6 

57-22 

42-78 


35-6 

57-14 

42-86 


3-7 

58-17 

41-83 


18-2 
58-09 

41-92 



The permanent gases generated by the explosion were found to occupy 



424 



CALCULATION OF THE FORCE OF FIRED GUNPOWDER. 



at 0° C. and at ordinary atmospheric pressure, about 280 times the volume 
of the original powder. 

The products of explosion furnished by 1 gramme of each powder, 
were — 





Pebble 


Rifle Large 






Powder. 


Grain. 




Potassium carbonate (K 2 CO s ), . 


•3258 


•3415 


•2861 


,, sulphate (K 2 S0 4 ), 


•0710 


■0844 


•1252 


,, sulphide (K.,S), 


•1042 


•0807 


•0999 


,, sulphocyanide (KCNS), 


•0014 


•0013 


•0007 


,, nitrate (KN0 3 ). 


•0013 


•0015 


•0009 


Ammonium carbonate, 


•0005 


•0004 


•0003 


Sulphur, . . • 


•0445 


•0490 


•0381 


Charcoal, ...... 

Total solid products, . 
Carbonic acid gas (C0 2 ), . 


•0008 


•0004 




•5495 


•5592 


•5512 


"2685 


•2630 


•2689 


Carbonic oxide (CO), 


•0477 


•0422 


•0355 


Nitrogen, ... ... 


•1123 


•1117 


•1123 


Sulphuretted hydrogen (H 2 S), . 


•0111 


■0109 


•0101 


Marsh gas (CH 4 ), .... 


•0006 


•0008 


•0004 


Hydrogen, ..... 


•0006 


•0009 


•0007 


Oxygen, 

Total gaseous products, 




•0002 


•0003 

•4282 


•4408 


•4297 



From this table it appears that the solid residue of fired gunpowder 
consists chiefly of carbonate and sulphate of potassium, with usually 
smaller proportions of sulphide of potassium. The gases evolved are 
chiefly carbonic acid gas and nitrogen, with a small quantity of carbonic 
oxide. 

The great variation in the proportions of sulphate and sulphide of 
potassium, coupled with our knowledge of the. mutual relations of these 
bodies at high temperatures, would support the belief that the sulphate 
is first produced, and is partially converted into sulphide by secondary 
reactions. 



311. Calculation of the Force of Fired Gunpowder.— The complex 
character of the decomposition, and its variation under different conditions, 
render it impossible to write a single general equation representing the 
explosion of gunpowder ; but in order to illustrate the method of calculat- 
ing the force of fired powder in any given case, we may take the following- 
equation as a simple expression of the principal reaction — 

4KNO s + C 4 + S = K 2 C0 3 + K 2 S0 4 + N 4 + 2C0 2 + CO . 



The mechanical force exerted in explosion depends upon the production 
of a large volume of gas from a small volume of solid, the volume of the 
gas being increased by the expansive effect of the heat generated in the 
combustion of the charcoal and sulphur. To calculate the amount of this 
mechanical force, it is necessary to ascertain the volume of gas which 
would be evolved by a given volume of powder, and the extent to which 
the gas would be expanded by the heat at the instant of explosion. 



CALCULATION OF THE FORCE OF FIRED GUNPOWDER. 425 



is calculated, 


from the Table of Atomic "Weights that — 

4KN0 3 = 101 x 4 = 404 grammes. 
C 4 = 12 x 4 = 48 
S = 32 

Gunpowder, . . 484 ,, 






Grammes. Litres at 0° C. and 7fiO c 


mm. Bar. 


N 4 


= 14 x 4 = 56 = 11-2 x 4 = 


44-8 


2C0 2 


= 44 x 2 = 88 = 22-4 x 2 = 


44-8 


CO 


= 28 


22'4 



Gaseous products, 172 112 

Hence it appears that 484 grammes of gunpowder would yield 112 litres 
of gas measured at 0° C. and 760 mm. barometic pressure. 

We have next to determine the volume of this gas at the moment of 
the explosion. 

The total heat produced in the explosion of 1 part by weight Of gun- 
powder was found by Noble and Abel to raise the temperature of 714*5 
parts by weight of water from 0° C. to 1° C, or to raise the temperature 
of 1 part by weight of water from 0° C. to 7 14° -5 C, supposing the water 
to be capable of bearing so great an elevation of temperature without 
change of state. 

This result is generally expressed by saying that the combustion of the 
powder evolves 714*5 units of heat (the unit of heat being the quantity 
required to raise 1 part by weight of water from 0° C. to 1° C). 

But the products of the explosion of powder will be raised to a higher 
temperature than 7 14° -5 C, because their specific heat is lower than that 
of water. 

For the purpose of this calculation, the specific heat of a substance may 
be defined as the quantity of heat required to raise 1 gramme of the 
substance through 1 ° of the thermometer, w T ater being taken as the unit. 

It is evident that if the specific heat of each product of the explosion 
be multiplied by the actual weight of that product, the result will be the 
quantity of heat required to raise that product 1° in temperature. 

The specific heats of the products have been ascertained by experiment, 
and are contained in the third column in the following table. The 
actual weight of each product from the explosion of 1 gramme of powder 
is contained in the second column, and the fourth column shows the 
quantity of heat required to raise each product 1° C. (representing as 
unity the quantity of heat required to raise 1 gramme of water from 0° C. 
to 1° C.):— 

Calculating from the above equation, the unit weight of gunpowder gives— 

Specific Heat. 



Potassium carbonate, . 


•28 


X 


•2162 


= 


•0605 


,, sulphate, . 


•36 


X 


•1901 


= 


•0684 


Nitrogen, . 


•12 


X 


•2438 


= 


•0293 


Carbonic acid gas, 


•18 


X 


•2163 


= 


•0389 


Carbonic oxide, . • ' . 


•06 


X 


•2450 


= 


•0147 



•2118 



The quantity of heat, therefore, which is required to raise, through 1° C. the joint 
products of the explosion of 1 gramme of gunpowder is 0*2118 of the above-mentioned 
unit of heat. 

Dividing the 714*5 units of heat generated in the explosion by the quantity of heat 



426 



PRESSURE OF FIRED GUNPOWDER. 



required to raise the joint products through 1°, we obtain 3373° C. for the number 
of degrees through which the products will be raised by the explosion. 

The expansion of gases when heated amounts to ij^r Q of their volume at 0° for 

Ho 

each degree of temperature. 

3373 
Hence 3373° would expand the gas by ~7^o~ = 12 times its volume at 0°, or each 

volume of gas at 0° would become 13 volumes at the moment of explosion. 

The 112 litres of gas from 484 grammes of powder would become 112x13, or 

1456 
1456 litres at the moment of explosion ; and 1 gramme of powder would give "Terr- 
or 3 '008 litres = 3008 cubic centimetres of gas. 

In an ordinary charge of gunpowder, 1 gramme occupies a space of one cubic centi- 
metre, but since, according to Noble and Abel, the fused solid products occupy one- 

2 
third of the volume of the original powder charge, there would be -x cubic centimetre 

to be occupied by the 3008 c.c. of gas. 

Since the elastic force or pressure of gases increases in proportion as their volume is 
diminished, the 3008 c.c. of gas, when confined in a space which would contain only 

g c.c. at the normal pressure of one atmosphere, must exert a pressure of 3008 x -^ 

= 4512 atmospheres or 4512 x 147 lbs., or 29*6 tons per square inch. 

The experiments of Noble and Abel gave 280 volumes of gas at 0° from one volume 
of powder, instead of 231 - 4 volumes, as required by the equation ; these 280 volumes 
would become 3640 volumes at the temperature of the explosion, and would exert a 
pressure of 5460 atmospheres in the space available for the gas ; this amounts to 
nearly 36 tons per square inch. 

Variations in the proportions of the ingredients of gunpowder have less effect upon 
the total energy of the powder than upon its rate of burning. Thus, a slowly burn- 
ing powder containing a large proportion of charcoal will exert the same pressure 
in a closed vessel as is exerted by military powder. For, when the proportion of 
carbon is large, more of the oxj'gen of the nitre is converted into carbonic oxide and 
less into carbon dioxide ; and a given quantity of oxygen, when converted into CO, 
gives twice as large a volume of gas as when converted into C0 2 . But the formation 
of C0. 2 , from a given weight of oxygen, developes 1*6 times as much heat as that of 
CO, so that the thermal value of a powder varies inversely as the volume of gas 
measured at 0° ; and the maximum pressure produced by the explosion is nearly the 
same for powders differing greatly in composition. This is illustrated by the results 
of Noble and Abel. 



Powder. 


Composition. 


Thermal 
Value. 


Gas at 0°. 


Maxm. Pressure 

in tons per sq. 

inch. 


Nitre. 


Ch. 


S. 


Mining, . . . 
Military, . . . 


67 
75 


19 

15 


14 
10 


509 

714 


360 

280 


44 
43 



In calculating the pressure, it is supposed, of course, that the whole of 
the gas is evolved at once, and is immediately raised- to the same tempera- 
ture, conditions never fulfilled in the use of gunpowder in small arms or 
in cannon, where the combustion of the charge is not instantaneous, but 
rapidly progressive, where the confining space is rapidly enlarged by the 
movement of the projectile long before the whole of the charge has 
exploded, and where the heated gas is cooled by contact with the metal 
of the piece. 

The calculation given above can be regarded only as an illustration of the method, 
as there are several circumstances which vitiate the conclusion arrived at. The 
chemical equation on which it is based is confessedly imperfect. 

We know little or nothing of the real condition of the products at the moment 
of the explosion ; it is probably very different from that after cooling, when we 
examine them. From what is known of the effect of heat upon carbonic acid gas and 



EXPLOSION OF POWDER UNDER VARIED CONDITIONS. 427 

carbonic oxide, it is almost certain that these gases are at least partially resolved into 
their elements at the moment of explosion, and it is scarcely likely that the complex 
molecules of sulphate and carbonate of potassium would exist at so high a tempera- 
ture. Any breaking up of the molecules of carbonic acid gas, sulphate and carbonate 
of potassium, would increase the expansion, and render the above estimate of the force 
of fired powder too low. 

It dissociation or temporary decomposition (see page 91) of the products occurs as 
a result of the high temperature, the acts of combination which must take place 
during the expansion and consequent cooling must be attended with evolution of 
heat, rendering the decrease of pressure more gradual than it would be otherwise. 

The actual rate of expansion of gases at so high a temperature is inferred from our 
experience of their behaviour at comparatively low temperatures, a ad there are some 
indications of a want of agreement under the two conditions. 

The experiments of Andrews have shown that, even at a pressure of 100 atmo- 
spheres, carbonic acid gas exhibits striking deviations from' the law that the pressure 
exerted by a gas is inversely as its volume. 

The period over which, the combustion of a given weight of powder 
extends will, of course, depend upon the extent of surface over which it 
can be kindled; thus a single fragment of powder weighing 10 grains, 
even if it were instantaneously kindled over its entire surface, could not 
evolve so much gas in a given time as if it had been broken into 10 
separate grains, each of which was kindled at the same instant, since the 
inside of the large fragment can only be kindled from the outside. Upon 
this principle a given weight of powder in large grains will occupy a 
longer period in its explosion than the same weight in small grains, so 
that the large grain powder is best fitted for ordnance, where the ball is 
very heavy, and the time occupied in moving it will permit the whole of 
the charge to be fired before the ball has left the muzzle, whilst in small 
arms with light projectiles, a finer grained and more quickly burning 
charge is required. If the fine grain powder. were used in cannon, the 
whole of the gas might be evolved before the containing space had been 
sensibly enlarged by the movement of the heavy projectile, and the gun 
would be subjected to an unnecessary strain; on the other hand, a large 
grain powder in a musket, would evolve its gas so slowly that the ball 
might be expelled with little velocity by the first half of it, and the 
remainder would be wasted. There is good reason to believe that even 
under the most favourable circumstances a large proportion of every 
charge of powder is discharged unexploded from the muzzle of the gun, 
and is therefore wasted. In blasting rocks and other mining operations, 
the space within which the powder is confined is absolutely incapable of 
enlargement until the gas evolved by the combustion has attained 
sufficient pressure to do the whole work, that is, to rend the rock, for 
example, asunder. Accordingly, a slowly burning charge will produce the 
effect, since the rock must give way when the gas attains a certain pres- 
sure, whether that happens in one second or in ten. Indeed, a slowly 
burning charge is advantageous, as being less liable to shatter the rock or 
coal, and bringing it away in larger masses with less danger. Nitrate of 
baryta and nitrate of soda are sometimes substituted for a part of the 
nitrate of potash in mining powder, its combustion being thus retarded. 

Espir's Hasting pmoder contains 60 per cent, of sodium nitrate, 14 of 
sulphur, and 26 of hard wood sawdust. 

The same charge of the same powder produces very different results when heated 
in different ways. If 5 grains of gunpowder be placed in a wide test-tube, and fired 
by passing a heated wire into the tube, a slight puff only is perceived ; but if the same 
amount of powder be heated in the tube by a spirit-lamp, it will explode with a loud 



428 EFFECT OF ATMOSPHERIC PRESSURE ON FIRED GUNPOWDER. 

report, and perhaps shatter the tube (a copper or brass tube is safer). In the first 
case the combustion is propagated slowly from the particle first touched by the wire ; 
in the second, all the particles are raised at once to pretty nearly the same tempera- 
ture, and as soon as one explodes, all the rest follow instantaneously. 

When gunpowder is slowly fired, the products of its decomposition are 
different from, those mentioned above ; thus, nitric oxide (NO), arising 
from incomplete decomposition of the nitre, is perceived in considerable 
quantity, and may be recognised by the red colour produced when it is 
brought in contact with air. 

The white smoke resulting from the explosion of gunpowder consists 
chiefly of the sulphate and carbonate of potassium in a very finely-divided 
state ; it seems probable that at the instant of explosion they are con- 
verted into vapour, and are afterwards deposited in a state of minute 
division as the temperature falls. The fouling or actual solid residue in 
the gun is very trifling when the powder is dry and has been well incor- 
porated ; a damp or slowly burning powder leaves, as might be expected, 
a larger residue. The residue always becomes wet on exposure to air, 
from the great attraction for moisture possessed by the carbonate and 
sulphide of potassium. 

When 10 grains of Waltham Abbey gunpowder are fired in a strong air-tight cylin- 
der, with a cavity about an inch high and half an inch in diameter, by the galvanic 
battery, the interior of the cavity is covered with a snow-white powder composed of 
sulphate and carbonate of potassium, which deliquesces rapidly in a damp atmosphere. 
No nitric oxide is found in the gas formed by the explosion. 

If a small quantity of powder be slightly damped and rammed into a wooden 
tube, in the mouth of which a piece of quick match is inserted, the charge may be 
kindled, and the tube held with its mouth under water, so that the gases may be 
collected in an inverted jar. These will be found to contain 1SIO (giving a brown 
colour in contact with air) H 2 S (giving a black precipitate with lead acetate) beside 
the C0. 2 (giving a white precipitate with lime water), CO and N. 

312. Effect of variations of atmospheric pressure on the combustion of 
gunpoivder.— From the circumstance that the combustion of gunpowder is 
independent of any supply of oxygen from the air, it might be supposed 
that it would be as easily inflamed in vacuo as under ordinary atmo- 
spheric pressure. This is not found to be the case, however, for a 
mechanical reason, viz., that the flame from the particles which are first 
ignited escapes so rapidly into the vacuous space, that it does not inflame 
the more remote particles. Tor a similar reason, charges of powder in 
fuzes are found to burn more slowly under diminished atmospheric 
pressure, the flame (or heated gas) escaping more rapidly and igniting less 
of the remaining charge in a given time. It has been determined that if 
a fuze be charged so as to burn for thirty seconds under ordinary atmo- 
spheric pressure (30 inches barometer), each diminution of 1 inch in 
barometric pressure will cause a delay of 1 second in the combustion of 
the charge, so that the fuze will burn for thirty-one seconds when the 
barometer stands at 29 inches. 

The manufacture of gunpowder may be illustrated by the following experiments on 
a small scale : — 

Preparation of the ingredients — Charcoal. — A few small pieces of wood are placed 
in a clay crucible, which is then filled up with dry sand and heated in a moderate 
fire as long as any vapours are evolved, when it may be set aside to cool. 

Sulphur. — 500 grains of roll sulphur may be distilled in a Florence flask, using 
another flask, the'neck of which has been cut off (fig. 278), for a receiver from which 
the suljmur is afterwards poured, in a melted state, upon a piece of tin-plate. 



CHEMISTRY OF FUEL. 



429 



Nitre.— 1000 grains of impure nitre are dissolved, at a moderate he'at, in 4 
measured ounces of distilled water, in an evaporating dish (fig. 279) ; the solution is 
filtered into a beaker which is placed in cold water, and stirred with a glass rod 
until it is quite cold. The saltpetre flour thus obtained is collected upon a filter, 
thoroughly drained, the filter removed from the funnel, spread out, the saltpetre 
transferred to another piece of filter paper, and pressed between the paper to remove 
as much of the liquid as possible ; it is then spread out on paper and dried on a hot 
brick. (For the mode of testing its purity see page 416. ) 





Fig. 278.— Distillation of 
sulphur. 



Fiff. 27! 



Mixture of the ingredients. — Sixty grains of the charcoal, reduced to a very fine 
powder, 40 grains of the sulphur, also previously powdered, and 300 grains of the 
dried nitre, are very intimately mixed in a mortar ; 50 grains of the mixture are set 
aside for comparison. To the remainder enough water is added to make it into a 
stiff cake, which is well incorporated under the pestle for some time. It is then 
scraped out of the mortar and allowed to dry slowly at a very gentle heat. When 
perfectly dry it is crumbled to a coarse powder, and the dust sifted out through a 
piece of wire gauze. It will be found instructive to compare, in trains and other- 
wise, the firing of the powder in grains, of the dust, and of the mixed ingredients 
without incorporation, observing especially the difference in rapidity of burning and 
in the amount of residue. 



CHEMISTRY OF FUEL. 

313. Several of the applications of chemical principles in the combus- 
tion of fuel have been already explained and illustrated. The object of 
this chapter is to compare the chemical composition of the most important 
varieties of fuel, and to exemplify the principles upon which their heating- 
power may be calculated from the results furnished by the analysis of the 
fuel. 

All the varieties of ordinary fuel, of course, contain a large proportion 
of carbon, always accompanied by hydrogen and oxygen, and sometimes by 
small proportions of nitrogen and sulphur. Certain mineral substances are 
also-contained in all solid fuels, and compose the ash when the fuel is burnt. 

For all practical purposes, it may be stated that the amount of heat 
generated by the combustion of a given weight of fuel depends upon the 
weights of carbon and hydrogen, respectively, which enter into combina- 
tion with the oxygen of the air in the act of combustion of the fuel. 

It has been ascertained by experiment that 1 lb. of carbon (in the 
form in which it exists in wood-charcoal), when combining with oxygen 
to form carbon dioxide, produces a quantity of heat which is capable of 
raising 8080 lbs. of water from 0° to 1° of the centigrade thermometer. 
This is usually expressed by saying that the calorific value of carbon is 
8080, or that carbon produces 8080 units of heat during its combustion to 



430 CALCULATION OF CALORIFIC VALUE OF FUEL. 

carbon dioxide. If the fuel, therefore, consisted of pure carbon, it would 
merely be necessary to multiply its weight by 8080 to ascertain its calorific 
value. 

One pound of hydrogen, daring its conversion into water by combustion, 
evolves enough heat to raise 34,400 lbs. of water from 0° C. to 1° C, so 
that the calorific value of hydrogen is 34,400. 

If the fuel consisted of carbon and hydrogen only, its calorific value 
would be calculated by multiplying the weight of the carbon in 1 lb. 
of the fuel by 8080, and that of the hydrogen by 34,400, when the sum 
of the products would represent the calorific value. Eut if the fuel 
contains oxygen already combined with it, the calorific value will be 
diminished, since this oxygen will, consume a part of the combus- 
tible without generating heat, because it already exists in a state of 
combination with the carbon and hydrogen of the fuel. For example, 
1 lb. of wood contains 0*5 lb. of carbon, 0-06 of hydrogen, and 0'44 
of oxygen. Now, oxygen combines with one-eighth of its weight of 
hydrogen to form water, so that the 0'44 lb. 6i oxygen will convert 
•44 -f- 8 = '055 of the hydrogen into water, without evolution of avail- 
able heat, leaving only 0-005 available for the production of heat. The 
calorific value of the wood, therefore, would be represented by the sum of 
0-005x34,400 ( = 172) and 0-5x8080 ( = 4040), which would amount 
to 4212; or 1 lb. of wood should raise 4212 lbs. of water from 0° C. to 
1°C. 

These considerations lead to the following general formula for calculat- 
ing the calorific value of 'a fuel containing carbon, hydrogen, and oxygen, 
where c, h, and o, respectively represent the carbon, hydrogen, and oxygen 
in 1 grain of fuel. 

The calorific value (or number of lbs. of water which might be heated 

by the fuel from 0° C. to 1° C.) = 8080 c + 34,400 (h - 



8080 c + 34,000 h - 4300 o. 

The calorific value of a fuel, as determined by experiment, is generally 
less than would be calculated from its chemical composition, in consequence 
of the absorption of a certain amount of heat attending the chemical 
decomposition of the fuel. In the case of compounds of carbon and hydro- 
gen, it has been observed that even when they have the same composition 
in 100 parts, they have not of necessity the same calorific value, the latter 
being affected by the difference in the arrangement of the component par- 
ticles of the compound, which causes a difference in the quantity of -heat- 
absorbed during its decomposition. Thus defiant gas (C 2 H 4 ) and cetylene 
(C 16 H 32 ) have the same percentage composition, and their calculated calorific 
values would be identical, but the former is found to produce 11,858 units 
of heat, and the latter only 11,055. As a general rule, however, it is found 
that the calorific values of the hydrocarbons which contain a multiple of 
CH 2 , agree more nearly with the calculated numbers than do those of 
hydrocarbons which belong to the marsh gas series. 

It must be remembered that the calorific value of a fuel represents the 
actual amount of heat which a given weight of it is capable of producing, 
and is quite independent of the manner in which the fuel is burnt. Thus, 
a hundredweight of coal will produce precisely the same amount of heat in 
an ordinary grate as in a wind-furnace, though in the former case the fire 
will scarcely be capable of melting copper, and in the latter it will melt 



CALCULATION OF CALORIFIC INTENSITY OF FUEL. 431 

steel. The difference resides in the temperature or calorific intensity of 
the two fires ; in the wind-furnace through which a rapid draught of air 
is maintained by a chimney, a much greater weight of atmospheric oxygen 
is brought into contact with the fuel in a given time, so that, in that 
time, a greater weight of fuel will be consumed and more heat will be 
produced ; hence the fire will have a higher temperature,. for the tem- 
perature represents, not the quantity of heat present in a given mass of 
matter, but the intensity or extent to which that heat is accumulated at 
any particular point. In the case of the wind-furnace here cited, a further 
advantage is gained from the circumstance that the rapid draught of air 
allows a given weight of fuel to be consumed in a smaller space, and, of 
course, the smaller the area over which a given quantity of heat is distri- 
buted, the higher the temperature within that area (as exemplified in the 
use of the common burning-glass). In some of the practical applications 
of fuel, such as heating steam-boilers and warming buildings, it is the 
calorific value of the fuel which chiefly concerns us, but the case is different 
where metals are to be melted, or chemical changes to be brought about 
by the application of a very high temperature, for it is then the calorific 
intensity, or actual temperature of the burning mass, which has to be con- 
sidered. No trustworthy method has yet been devised for determining 
by direct experiment the calorific intensity of fuel, and it is therefore 
ascertained by calculation from the calorific value. 

Let it be required to calculate the calorific intensity, or actual tempera- 
ture, of carbon burning in pure oxygen gas. 

Twelve lbs. of carbon combine with 32 lbs. of oxygen, producing 44 lbs. 
of C0 2 ; hence 1 lb. of carbon combines with 2 67 lbs. of oxygen, pro- 
ducing 3'67 lbs. of C0 2 . It has been seen above that 1 lb. of carbon 
evolves 8080 units of heat, or is capable of raising 8080 lbs. of water 
from 0° to 1° C, or, on the supposition that the water would bear such an 
elevation of temperature, the 1 lb. of carbon would raise 1 lb. of water 
from 0° to 8080° C. If the specific heat (or heat required to raise 1 lb. 
through 1°, see page 425) of C0 2 were the same as that of water, 8080° 
divided by 3*67 would represent the temperature to which the 3*67 lbs. 
of C0 2 would be raised, and therefore the temperature to which the solid 
carbon producing it would be raised in the act of combustion. But the 
specific heat of carbonic acid gas is only 0'2163, so that a given amount 
of heat would raise 1 lb. of C0 2 to nearly five times as high a temperature 
as that to which it w T ould raise 1 lb. of water. 

Dividing the 8080 units of heat (available for raising the temperature 
of the C0 2 ) by 0-21(53, the quantity of heat required to raise 1 lb. of C0 9 
through 1°, we obtain 37,355 for the number of degrees through which 
1 lb. of C0 2 might be raised by the combustion of 1 lb. of carbon. But 
there are 3*67 lbs. of C0 2 formed in the combustion, so that the above 
number of degrees must be divided by 3 - 67 in order to obtain the actual 
temperature of the C0. 2 at the instant of its production, that is, the 
temperature of the burning mass. The calorific intensity of carbon burn- 
ing in pure oxygen is, therefore (37,355° C. -f- 3*67 = ) 10,178° C. or 
18,352° F. But if the carbon be burnt in air, the temperature will be far 
lower, because the nitrogen of the air will absorb a part of the heat, to 
which it contributes nothing. The 2-67 lbs. of oxygen required to burn 
1 lb. of carbon would be mixed, in air, with 8*93 lbs. of nitrogen, so that 
the 8080 units of heat would be distributed over 3 '67 lbs. of carbonic 



432 CALCULATION OF CALORIFIC INTENSITY OF FUEL. 

acid gas, and 8*93 lbs. of nitrogen. Since the specific heat of carbonic 
acid gas is 0*2163, the product of 3*67 x 0*2163 (or 0*794) represents the 
quantity of heat required to raise the 3*67 lbs. of C0 9 from 0° to 1° C. 

The specific heat of nitrogen is 0*2438, hence 8*93"x 0*2438 (or 2*177) 
represents the quantity of heat required to raise the 8*93 lbs. of atmo- 
spheric nitrogen from 0° to 1° C. 

Adding together these products, we find that 0*794 + 2*177 = 2*971 
represents the quantity of heat required to raise both the nitrogen and 
carbonic acid gas from 0° to 1° C. 

Dividing the 8080° by 2*971, we obtain 2720° C. (4928° F.) for the 
number of degrees through which these' gases would be raised in the com- 
bustion, i.e., for the calorific intensity of carbon burning in air. By heat- 
ing the air before it enters the furnace (as in the hot-blast iron furnace) 
of course the calorific intensity would be increased ; thus if the air be 
introduced into the furnace at a temperature of 600° F., it might be stated, 
without serious error, that the temperature producible in the furnace 
would be 5528° F. (4928° + 600°). The temperature might be further 
increased by diminishing the area of combustion, as by employing very 
compact fuel and increasing the pressure of the blast. 

In calculating the calorific intensity of hydrogen burning in air, from 
its calorific value, it must be remembered that in the experimental deter- 
mination of the latter number, the steam produced in the combustion was 
condensed to the liquid form, so that its latent heat was added to the 
number representing the calorific value of the hydrogen j but the latent 
heat of the steam must be deducted in calculating the calorific intensity, 
because the steam goes off from the burning mass and carries its latent 
heat with it. 

One lb. of hydrogen, burning in air, combines with 8 lbs. of oxygen, 
producing 9 lbs. of steam, leaving 26*77 lbs. of atmospheric nitrogen, and 
evolving 34,400 units of heat. 

It has been experimentally determined that the latent heat of steam is 
537° C, that is, 1 lb. of water, in becoming steam, absorbs 537 units of 
heat (or as much heat as would raise 537 lbs. of water from 0° to 1° C.) 
without rising in temperature as indicated by the thermometer. The. 
9 lbs. of water produced by the combustion of 1 lb. of hydrogen will 
absorb, or render latent, 537 x9 = 4833 units of heat. Deducting this 
quantity from the 34,400 units evolved in the combustion of 1 lb. of 
hydrogen, there remain 29,567 units of heat available for raising the tem- 
perature of the 9 lbs. of steam and 26*77 lbs. of atmospheric nitrogen. 
The specific heat of steam being 0*480, the number (0*480x9 = ) 4*32 
represents the quantity of heat required to raise the 9 lbs. of steam 
through 1° 0. ; and the specific heat of nitrogen (0*2438) multiplied by 
its weight (26*77 lbs.), give 6*53 units of heat required to raise the 
26*77 lbs. of nitrogen through 1° C. By dividing the available heat 
(29,567 units) by the joint quantities required to raise the steam and 
nitrogen through 1° C. (4*32 + 6*53 = 10*85), we obtain the number 2725° 
C. (4937° F.) for the calorific intensity of hydrogen burning in air. 



The method of calculating. the calorific intensity of a fuel composed of carbon, 
hydrogen, and oxygen will now be easily followed. 

Let c and h respectively represent the weights of carbon and hydrogen in 1 lb. 

of fuel, and o that of oxygen. Then — - - = weight of hydrogen required to convert 



COMPOSITION AND VALUE OF FUELS. 



433 



the oxygen into water, and h - — represents the hydrogen which is available for the 
8080 c + 34,400 fh — — ) represents the calorific value in °C, 



production of heat. 
= 8080 c + 34,400 h 



4300 o. 



8h 



and 



2 "67 c = atmospheric oxygen consumed by the carbon; 8 \h - -jt-J 

atmospheric oxygen consumed by the hydrogen available as fuel. 

3-34 (2-67 c + 8 h - o) = atmospheric nitrogen = 8*92 c + 26*72 h - 3*34 o. 

Multiplying this by the specific heat of nitrogen 0-2438, we obtain — 
2-17 c + 6-51 h - - 81 o for the heat required to raise the nitrogen through 1° C. 

0-794 c represents the quantity of heat required to raise the C0 2 through 1° C. 
4-32 h is the heat required to raise the steam through 1°. Accordingly, the available 
heat, 8080 c+ 34,400 h - 4300 o, must be divided by 0"794 c + 4 -32 h + (2-17 c 
+ 6'51 h-0'81 o), or 2 -96 c + 10 '83 h - -81 o in order to obtain the calorific intensity. 

Hence, the calorific intensity, in centigrade degrees, of a fuel composed of carbon, 
hydrogen, and oxygen, is represented by the formula — 
8080 c + 34,400 h - 4300 o 
2-96 c + 10-83 h - 0-81 o. 
The actual calorific intensity of the fuel is not so high as it should be 
according to theory, because a part of the carbon and hydrogen is con- 
verted into gas by destructive distillation of the fuel, and this gas is not 
actually burnt in the fire, so that its calorific intensity is not added to that 
of the burning solid mass. Again, a portion of the carbon is converted 
into carbonic oxide (CO), especially if the supply of air be imperfect, 
and much less heat is produced than if the carbon were converted into 
carbon dioxide ; although it is true that this carbonic oxide may be con- 
sumed above the tire by supplying air to it, the heat thus produced does 
not increase the calorific intensity or temperature of the fire itself. 

One lb. of carbon furnishes 2*33 lbs. of carbonic oxide. These 2*33 
lbs. of carbonic oxide evolve, in their combustion, 5599 units of heat. 
But if the 1 lb. of carbon had been converted at once into carbon dioxide, 
it would have evolved 8080 units of heat, so that 8080 - 5599, or 2481, 
represents the heat evolved during the conversion of 1 lb. of carbon into 
carbonic oxide, showing that a considerable loss of heat in the fire is caused 
by an imperfect supply of air. It has been already pointed out, in the 
section relating to Coal, that the formation of carbonic oxide is sometimes 
encouraged with a view to the production of a flame from non-flaming 
coal, such as anthracite. 

The following table exhibits the average percentage composition of the 
principal varieties of fuel (exclusive of ash), together with their calculated 
calorific values and intensities : — 





Carbon. 


Hydrogen. 


Oxygen. 


Nitrogen. 


Sulphur. 


Calorific 
Value. — Intensity. 


Wood (Oak) . 

Peat, 

Lignite (Bovey), 

Bituminous coal, 

Cliarcoal, 

Anthracite, 

Coke, 


50-18 
6153 
67-86 
79-38 
90-44 
91-86 

97-32 


6-08 
5-64 
5-75 
5-34 
2-91 
3 33 

0-49 


43-74 
32-82 
23-39 
13-01 
6-63 
3-02 


6-57 

1-85 

0-84 


2-41 
0-39 

0-92 


4212° C. 

5654 

6569 

7544 

8003 

8337 

8009 


2380° C. 

2547 
2628 
2694 
2760 
2779 

2761 


2-17 



In all ordinary fires and furnaces, a large amount of heat is wasted in 
the current of heated products of combustion escaping from the chimney. 

2 E 



434 REGENERATIVE FURNACE. 

Of course, a portion of this heat is necessary in order to produce the 
draught of the chimney. In boiler furnaces it is found that, for this pur- 
pose, the temperature of the air escaping from the chimney must not be 
lower than from 500° to 600° F. If the fuel could be consumed by sup- 
plying only so much air as contains the requisite quantity of oxygen, a 
great saving might be effected, but in practice about twice the calculated 
quantity of air must be supplied in order to effect the removal of the 
products of combustion with sufficient rapidity. 

Much economy of fuel results from the use of furnaces constructed on 
the principle of Siemens' regenerative furnace, in which the waste heat of 
the products of combustion is absorbed by a quantity of firebricks, and 
employed to heat the air before it enters the furnace, two chambers of 
firebricks doing duty alternately, for absorbing the heat from the issuing 
gas, and for imparting heat to the entering air, the current being reversed 
by a valve as soon as the firebricks are strongly heated. 

(For the principles of smoke prevention, and other particulars of the 
chemistry of fuel, see Coal.) 



ORGANIC CHEMISTRY. 



314. Although it is impossible to propose a definition of the term 
organic substance which shall not be applicable to some of the substances 
commonly regarded as inorganic, it is found advantageous for the purposes 
of study to treat organic chemistry as a separate division of the science, 
dealing especially with those substances which are usually obtained, 
either directly or indirectly, from animals and vegetables. 

One very important distinction between organic and inorganic substances 
is, that the former are for the most part composed of carbon, hydrogen, 
nitrogen, and oxygen, in different proportions and in various modes of 
arrangement, and that they are, therefore, much more frequently con- 
vertible into each other by metamorphosis, without extraneous addition 
of matter, than inorganic substances are. 

It has been already pointed out that the chemist is gradually learning 
to produce, though by somewhat clumsy and circuitous processes, many of 
the substances which were formerly believed incapable of being formed, 
except through the intervention of life ; but no substance possessing an 
organised structure, such as woody fibre, or muscular fibre, and no ab- 
solutely indispensable organic constituent of animal or vegetable frames, 
has yet been artificially procured. 

It will not escape notice that the four elements which compose the 
greater number of organic substances, viz., hydrogen, oxygen, nitrogen, 
and carbon, are, respectively, monatomic, diatomic, triatomic, and tetra- 
tomic elements (page 247), and are, therefore, capable of forming a greater 
variety of compounds than would be the case if they were elements of 
equal atomicities. 

Classification of Organic Compounds. 

In order to classify organic bodies, it is necessary to ascertain — 

(1) Their empirical formula, which denotes the relative numbers of 
atoms of their elements. 

(2) Their molecular formula, denoting the absolute number of atoms 
in one molecule. 

(3) Their rational on structural formula, denoting the mode of arrange- 
ment of the atoms in the molecule. 

The empirical formula is at once deduced from the ultimate analysis of 
the organic substance, as described at pp. 84 and 132. 

The molecular formula is ascertained by determining the molecular 
weight of the compound. 

When the compound is capable of conversion into vapour without 
decomposition, its molecular weight is determined by converting a definite 



436 CLASSIFICATION OF ORGANIC COMPOUNDS. 

weight of the compound into vapour, and measuring it. The molecular 
weight is that weight which occupies the same volume as two unit weights 
of hydrogen, at the same temperature and pressure. 

Thus, 46 grains of alcohol, when converted into vapour, occupy the 
same volume as 2 grains of hydrogen. Hence, the molecular weight of 
alcohol is 46. 

Now, by ultimate analysis, it is found that 100 parts of alcohol contain 
52*18 of carbon, 13*04 hydrogen, and 34*78 oxygen. Hence, 1 molecule, 
or 46 parts, contain 24 parts or 2 atoms of carbon, 6 parts or 6 atoms 
hydrogen, and 16 parts or 1 atom oxygen, and the molecular formula of 
alcohol is C 2 H 6 0. 

But when the substance cannot be vaporised without decomposition, 
its molecular weight must be determined by other methods, as exempli- 
fied in the case of oxalic acid at p. 85, and in that of urea at p. 132. 

In order to deduce the rational formula of a compound, all its reactions 
(or decompositions with other compounds) must be carefully studied, and 
that arrangement of its atoms must be adopted which best explains the 
greater number of the reactions. 

For example, it is found that when alcohol is acted on by other bodies, 
its decomposition is most easily explained, in the greater number of cases, 
by regarding it as composed after the model of the water molecule H 2 0, 
in which 1 atom of hydrogen is replaced by the group C 2 H 5 (ethyle). 
Hence, the rational or structural formula of alcohol is C 2 H 5 .OH. 

The examination of the optical properties of organic compounds, 
especially as to their power of refracting light, of influencing its polarisa- 
tion, and of absorbing certain portions of the spectrum, is found of great 
assistance in ascertaining their constitution. 

When the molecular and rational formulae of a compound have been 
ascertained, it may generally be assigned to one of the following divisions 
of organic substances : — 

Chief Classes of Organic Compounds. 
6. Ethers. 



1. Hydrocarbons. 

2. Alcohols. 

3. Aldehydes. 

4. Acids. 

5. Ketones. 



7. Organo-metallic bodies. 

8. Ammonia derivatives. 

9. Cyanogen compounds. 



1. The Hydrocarbons are all composed of carbon and hydrogen only, 
and constitute the largest class of organic compounds. The simplest 
example of this class is marsh gas or methane CH 4 , to which it is usual 
to assign the rational formula H 3 C.H which represents it as methyle 
hydride, the group H 3 C representing tetratomic carbon (p. 248), of which 
three out of the four bonds of chemical attraction (p. 249) are satisfied 
by hydrogen, so that the fourth bond is available for attachment to any 
other element or group of elements ; hence methyle is designated a 
monatomic radical, and will be found to play a most important part in 
the formation of organic compounds. 

The term methyle is derived from piBv, ivine, and v\rj, wood, because 
its principal compound is a spirituous substance resulting from the dis- 
tillation of wood. The ending -yle is generally bestowed upon compound 
radicals, because vXy also means the matter of which a thing is made.* 

* The omission of the final e, so common in modern chemical writings, obscures the 
derivation. 



ALDEHYDES — ACIDS — KETONES. 437 

2. The Alcohols are compounds of carbon, hydrogen, and oxygen, con- 
structed upon the model of water in which one half of the hydrogen is 
replaced by a compound radical, which is very generally composed of 
carboD and hydrogen. 

Thus methyle alcohol is H 3 C.OH or methyle hydrate, i.e., water in 
which an atom of hydrogen is replaced by methyle. 

The group or radical OH is termed hydroxyle, and is evidently mon- 
atomic, because one of the two bonds of the diatomic oxygen is satisfied 
by the hydrogen atom, leaving the other bond available for the attach- 
ment of another element or group. 

The methyle alcohol H 3 C.OH is evidently derived from the methyle 
hydride H 3 C.H by the substitution of hydroxyle, OH, for hydrogen, and 
this substitution may be effected in two operations, which are very gene- 
rally employed in similar cases. 

(1) H 3 C.H (Methyle hydride) + Cl 2 = H S C.C1 {Methyle chloride) + HC1. 

(2) HgC.Cl + K.OH (Potassium hydrate) = KC1 + H3C.OH (Methyle alcohol). 

3. The Aldehydes, or de-hydrogenised alcohols, are products of oxida- 
tion of the alcohols, whereby hydrogen has been removed. Thus — 

H3C.OH (Methyle alcohol) + = H 2 + H 2 CO (Methyle aldehyde). 
In the methyle aldehyde, two bonds of the carbon atom are united to the 
diatomic oxygen atom, and the other two bonds to the two hydrogen atoms. 

4. The Acids result from a further oxidation of the alcohols, by which 
not only is hydrogen removed, but oxygen fills up the vacancy thus left. 
For example — 

f HO 
H 3 C, OH (Methyle alcohol) + 2 = H 2 + OC I H (Formic acid). 

The acids contain the group or radical termed oxatyle (6£6<s, acid), 
OC.OH, which is monatomic, because two of the four bonds of the tetra- 
tomic carbon are satisfied by the diatomic oxygen, and a third by the 
monatomic hydroxyle (OH), leaving a fourth bond available for the 
attachment of another element or group. 

5. The Ketones are derived from the acids by the substitution of a 
hydrocarbon radical for hydroxyle. 

a t-- -a r\n f ^H Acetic ketone ^ n ( CHo 

Acetic add, OC j ^ (acetone)) OC | CH » 

Hence, the ketones contain the diatomic group carbonyle, OC, combined 
with two hydrocarbon radicals. 

6. The ethers are derived from the alcohols by the substitution of a 
compound radical for the hydrogen in the hydroxyle group. 

Methyle alcohol, H 3 C.OH; Methyle ether, H 3 C.O.CH 3 . 

One method of converting an alcohol into an ether is shown in the 
following equations : — 

(1) Tl B C.OH. (Methyle hydrate) + N&--=~K 3 C.01$ei (Sodiiimmethylate) + H. 

(2) H 3 C.OXa + H 3 CI (Methyle iodide) =JSaI + H 3 C.O.CH 3 (Methyle ether). 

7. The Organo-metallic bodies are derived from the alcohols by .the 
substitution of a metal for the hydroxyle. 

Methyle alcohol, H 3 C.OH ; 
Sodium-methyle, H 3 C.lN T a ; Zinc-methyle, H 3 C.Zn.CH 3 



438 



HYDROCARBONS. 



8. The Ammonia derivatives are formed from ammonia by the substi- 
tution of a compound radical for hydrogen. 

Ammonia, NH 3 ; Methylamine, H 3 C.NH 2 ; Dimethylamine, (H S C) 2 JH; 
Trimethylamine, N(CH 3 ) 3 . 

9. The Cyanogen compounds are those which contain the radical CN, 
which is monatomic, because only three of the bonds of the tetratomic 
carbon are satisfied by the triatomic nitrogen. 

Hydrocarbons. 

The hydrocarbons are divided into series, in each of which a definite 
ratio exists between the atoms of hydrogen and carbon. The most im- 
portant of these series are shown in the following table, in which n repre- 
sents a whole number : — 



Table 


of Hydrocarbons. 


Name of Series. 


General Formulae. 


Examples. 


Paraffines, . 


C„H,„+ 2 


CH 4 Methane. 


Olefines," . 


C n H 2 M 


C 2 H 4 Ethene. 


Acetylenes, 


C„H LM _ 2 


C 2 H 2 Ethine. 


Terpenes, . 


O n H. M _ 4 


C 10 H 16 Turpentine. 


Benzenes, . 


C„H. M _ a 


C 6 H 6 Benzene. 


Cinnamenes, 


C„H M _ 8 


C 8 H 8 Cinnamene. 


Naphthalenes, . . ' 


L/rc-ti _n — j2 


C 10 H 8 Naphthalene. 


Anthracenes, 


^ji-tlji- jg 


C 14 H 10 Anthracene. 



In any given series of hydrocarbons, the successive members of the 
series will be seen to differ by CH 2 or by some multiple of CH 2 . Thus, 
in the series of paraffines, we have 



_ 4 , ^2^6> 
Methane. Ethane. 



CEL 



C 3 H 8 , 



C 4 H 10 , &c. 

Butane. 



Propane. 

This is due to the successive methylation or replacement of hydrogen by 
methyle : thus — 

"h 3 c.h, H 3 C.CH 3 , H 3 C.CH 2 (CH 3 ), H 3 C.CH 2 .CH 2 (CH 3 ) 

Methane. Ethane. Propane. Butane. 

A series of compounds of which the members differ thus by CH 2 is said 
to be homologous (o/xoios, like, \oyos, propoiiion), and the members are 
homologues. 

Compounds occupying similar positions in different series are said to 
be isologous (io-os, equal). 

In the following table, A, B, and C are three homologous series, whilst 
1, 2, 3, and 4 are isologous series : — 





l 


2 


3 


4 


A 
B 
C 


CH 4 
CH 2 


C 2 H fi 
C 2 H 4 
C 2 H 2 


C 3 H 8 

^3 H 6 

C 3 H 4 


C 4 H 10 

C 4 H 8 
C 4 H 6 



The number of the hydrocarbons is very great, because the same 
number of atoms of C and H may form different compounds according to 
their grouping. 



CYANOGEN AND ITS COMPOUNDS. 439 

Thus, there are three hydrocarbons which have the same molecular 
formula, C 5 H 12 , but which are altogether different bodies. This may be 
accounted for by the difference in their rational or structural formulae. 

Normal pentane, H S C(CH 2 )(CH 2 )(CH 2 )CH 3 . 



Isopentane, . H 3 C(CH 2 )(CH) i ^ 

V 't 



HqC ) <~, f CHo 



Neopentane, . Jp [ C j 



3- , , CH, 

Compounds which contain the same elements in the same proportions, 
but yet have different properties, are said to be isomeric or isomerides 
(10-09, equal, /x€po<s, a part). 

When it is known that the grouping of their atoms is different, they 
are also termed metameric or metamerides. 

Compounds, of which the molecular formulae are multiples of each 
other by some whole number, are polymeric or polymerides (tto\v<s, many) ; 
thus benzene, C 6 H 6 , is a polymeride of acetylene C 2 H 2 . 

In the following pages, the strictly scientific classification of organic 
substances has not been adhered to, since it would often render it neces- 
sary to describe, in separate sections, substances which are, in nature, 
closely connected with each other, but an empirical arrangement has been 
followed, so that the reader may find his memory assisted, and the interest 
of the subject sustained, by being enabled to bring the facts and explana- 
tions into immediate connection with familiar processes of ordinary life.* 

One of the most conspicuous substances standing upon the boundary 
between organic and inorganic chemistry is the compound of carbon and 
nitrogen known as cyanogen, which is intimately connected with inorganic 
substances through some of the processes for its production, and through 
its similarity to the chlorine group of elements, whilst the origin and 
chemical properties of a large number of its compounds give them a claim 
to be ranked among organic substances. The study of this substance, 
therefore, will form a fit introduction to organic chemistry. 

CYANOGEN AND ITS COMPOUNDS. 

315. In the beginning of the last century, a manufacturer of colours at 
Berlin accidentally obtained a blue powder when precipitating sulphate of 
iron with potash. This substance was used as a colour, under the name 
of Prussian blue, for several years, before any explanation of its production 
was attempted, or even before the conditions under which it was formed 
were exactly determined. In 1724 it was shown that Prussian blue could 
be prepared by calcining dried animal matters with carbonate of potash, 
and mixing the aqueous solution of the calcined mass, first with sulphate 
of iron and afterwards with hydrochloric acid ; but the most important step 
towards the determination of its composition w r as made by Macquer, who 
found that by boiling it with an alkali, Prussian blue was decomposed, 
yielding a residue of red oxide of iron, and a solution which reproduced 
the blue when mixed with a salt of iron, from which he inferred that the 

* The number of organic substances known to the chemist is so great that a mere list of 
them would occupy a volume. In the present work a selection has been made of those 
which are interesting for their practical applications, or instructive from theoretical con- 
siderations. 



440 YELLOW PRUSSIATE OF POTASH. 

colour was a compound of the oxide of iron with an acid for which the 
alkali had a more powerful attraction — a belief confirmed, in 1782, by 
Scheele's observations, that when an alkaline solution prepared for making 
the blue was exposed to the air, or to the action of carbonic acid, it lost 
the power of furnishing the colour, but the escaping vapour struck a blue 
on paper impregnated with oxide of iron. Scheele also prepared this acid 
in a pure state, and it soon after obtained the name of prussic acid. 

In 1787, Berthollet found prussic acid to be composed of carbon, 
hydrogen, and nitrogen, but he also showed that the power of the alka- 
line liquor to produce Prussian blue depended upon the presence of a 
yellow salt crystallising in octahedra, and containing prussic acid, potash, 
and oxide of iron, though the latter was so intimately bound up with the 
other constituents, that it could not be separated by those substances 
which are usually employed to precipitate iron. 

Porrett, in 1814, applying the greatly increased resources of chemistry 
to the investigation of this subject, decomposed Prussian blue with baryta, 
and subsequently removed the baryta from the salt thus obtained by 
means of sulphuric acid, when he obtained a solution of the acid, which 
he named ferruretted chyazic acid. 

In 1815 Gay-Lussac, having boiled Prussian blue (or prussiate of iron, 
as it w T as then called) with red oxide of mercury and water, and crystal- 
lised the so-called prussiate of mercury, exposed it, in the dry state, to the 
action of heat, and obtained a gas having the composition CN, which was 
called cyanogen* in allusion to its connexion with Prussian blue. It 
was then seen that the substance which had been called ferruretted chyazic 
acid contained iron and the elements of cyanogen, whence it was called 
ferrocyanic acid, and its salts were spoken of as ferrocyanates. Robiquet 
first obtained this acid in the crystallised state, having the composition 
C 6 H 4 N 6 Fe ; and since it was found that, when brought in contact with 
metallic oxides, it exchanged the H 4 for an equivalent quantity of the 
metal, according to the equation— 

H 4 .C 6 N 6 Fe + 2M"0 = M 2 ".C 6 X 6 Fe + 2H 2 , 
it was concluded that the C 6 N 6 Fe composed a distinct group or radical,- 
which was named ferrocyanogen, Fey, the acid being called hydroferro- 
cyanic acid, and the salts ferrocy anides. 

316. Prussiate of potash. —The yellow prussiate of potash or potassium 
ferrocy anide (K 4 C 6 N 6 Fe.3Aq.) is manufactured upon a large scale by 
a process which is the more interesting because it turns to account some 
of the commonest kinds of refuse, such as old leather, hoof-parings, 
blood, and, in short, any animal matter rich in nitrogen, and not appli- 
cable to any more economical purpose. Sometimes these substances are 
first subjected to destructive distillation for the carbonate of ammonia 
which they are capable of yielding, and the residual highly nitrogenised 
charcoal is then used for the production of the ferrocyanide of potassium. 
Such matters are fused in an iron vessel with carbonate of potash and iron 
filings, and the fused mass is heated with water in open boilers, when a 
yellow solution is obtained, which, after evaporation, deposits truncated 
pyramidal crystals of ferrocyanide of potassium, containing three molecules 
of water. 

The production of the ferrocyanide may be explained in the following 

* From nvaveos, blue. 



PRUSSIAN BLUE. 441 

manner : — (1) The carbon containing nitrogen decomposes the potassium 
carbonate at a high temperature, producing potassium cyanide and car- 
bonic oxide gas ; K 2 C0 3 + C 4 + X 2 = 2KCX + 3CO. (2) Sulphur, derived 
partly from the animal matters and partly from potassium sulphate 
present as an impurity in the potashes, combines with the iron to form 
ferrous sulphide. (3) On treating the fused mass with water, the 
ferrous sulphide is dissolved by the potassium cyanide, yielding potassium 
sulphide and ferrocyanide — 

FeS + 6KCN = K 4 Fe(CX) 6 + K 2 S . 

Since the presence of the potassium sulphide in the liquor somewhat 
hinders the crystallisation of the ferrocyanide, some makers simply melt 
pure potassium carbonate with the animal charcoal, extract the potassium 
cyanide from the residue by treatment with water, and digest the solution 
with finely-ground spathic iron ore (ferrous carbonate) — 

FeC0 3 + 6KCX = K 4 Fe(CN) 6 + K 2 C0 3 . 

Prussian blue. — TVhen solution of ferric sulphate is added to one of 
potassium ferrocyanide, a very dark blue precipitate is obtained, which, 
when thoroughly washed, is soluble in pure water. This is used by dyers 
under the name of soluble Prussian blue, and is formed thus — 

2K 4 Fcy + Fe 2 (S0 4 ) 3 = 3K 2 S0 4 + K 2 Fe 2 Fcy 2 ; 

showing that the soluble blue is a potassio-ferric ferrocyanide. If potas- 
sium ferrocyanide be added to solution of ferric sulphate, the precipitated 
Prussian blue is not soluble; 2Fe 2 (S0 4 ) 3 + 3K 4 Fcy = 6K. 9 S0 4 + Fe 4 Fcy 3 . 
The Prussian blue is ferric ferrocyanide, the 4 atoms of triatomic iron 
saturating the 3 atoms of the tetratomic group ferrocyanogen, Fe"Cy' 6 . 
This compound radical has never yet been obtained in the separate state, 
but it can be traced through a complete series of compounds, in which it 
exactly resembles chlorine in its chemical relations; thus the hydroferro- 
cyanic acid (H 4 Fcy), and the ferrocyanides of the metals, are perfectly 
analogous to hydrochloric acid and the chlorides, though containing a 
compound radical instead of a simple one ; but whereas chlorine is a 
monatomic radical combining only with 1 atom of hydrogen, ferrocyano- 
gen is tetratomic. Oxalic acid is capable of dissolving Prussian blue, and 
this solution forms the basis of ordinary blue ink. 

Prussian blue is sometimes prepared with the green sulphate of iron 
(FeS0 4 ), but in that case it is necessary to expose the precipitate for 
some time to the air, since the first result is a nearly white precipitate * 
of potassio-ferrous ferrocyanide; K 4 Fcy + FeS0 4 = K 2 S0 4 + K 9 Fe"Fcy. 
When this precipitate is exposed to the air, it gradually acquires a 
dark blue colour, becoming eventually converted into Prussian blue by 
oxidation ; 6K 2 FeFcy + O s = 3K 4 Fcy + Fe 4 Fcy 3 + Fe 9 3 . 

Prussian blue is easily decomposed bv alkalies, a brown residue of ferric 
oxide being left, Fe 4 Fcy 3 + 12KHO = 3K 4 Fcy+ 2Fe 2 3 + 6H 2 0. This 
decomposition is turned to account. by the calico-printer for producing a 
buff or white pattern upon a blue ground. The stuff having been dyed 
blue by passing, first through a solution of per-salt of iron, and afterwards 
through one of potassium ferrocyanide, the pattern is discharged by an 
alkali, which leaves the brown peroxide of iron capable of being removed 

* This precipitate may be obtained perfectly white by shaking iron filings with solution 
of sulphurous acid, and filtering into a weak solution of potassium ferrocyanide. 



442 HYDROCYANIC OR PRUSSIC ACID. 

by a dilute acid, when the stuff has been rinsed, so as to leave the design 
white. 

Hydroferrocyanic acid. — By decomposing a cold saturated solution of 
potassium ferrocyanide with about an equal volume of hydrochloric acid, 
colourless crystals of hydroferrocyanic acid (H 4 Fcy) are obtained, which 
are insoluble in hydrochloric acid, but readily soluble in water. When 
a solution of this acid is heated, it evolves hydrocyanic acid (HCN), and 
deposits a white precipitate of ferrous ferrocyanide, Fe 2 Fcy, which becomes 
blue on exposure to the air, being converted into Prussian blue. 

The decomposition of the hydroferrocyanic acid by heat is represented 
by the equation, 3H 4 Cy 6 Fe = 12HCy + Fe 2 (FeCy 6 ), 

Hydroferro- Hydrocyanic Ferrous ferro- 

cyanic acid, acid, cyanide, 

and the formation of Prussian blue from this last compound on exposure 
to air by 3Fe 2 Fcy + 3 = Fe 4 Fcy 3 + Fe 2 3 . 

Hydrocyanic or Prussic acid. — Advantage is taken of the decomposition 
of potassium ferrocyanide by acids, in the preparation of solution of 
hydrocyanic acid for medicinal use. For this purpose, 2 parts of potassium 
ferrocyanide in powder are distilled with 1 \ parts of oil of vitriol diluted 
with 2 parts of water, the vapour of hydrocyanic acid being carefully 
condensed (see fig. 47). The decomposition of the ferrocyanide by the 
sulphuric acid yields hydroferrocyanic acid, which is then decomposed as 
in the equation given above. There is left in the retort the ferrous 
ferrocyanide as a pale greenish salt, which rapidly becomes blue when 
exposed to the air. 

The solution of hydrocyanic acid thus obtained is colourless, and 
exhales the remarkable odour of the acid ; its acid characters are 
very feeble indeed, even more so than those of carbonic acid, but 
it is extremely poisonous, a very small dose destroying life almost 
immediately. Hydrocyanic acid is found in laurel water, and in water 
distilled from the kernels of many stone fruits, such as the peach, apricot, 
and plum. In minute doses hydrocyanic acid is a very valuable remedy, 
and is employed in medicine in solutions of different strengths. One of 
these, which is known as the acid of the London Pharmacopoeia, contains 
2 per cent, of hydrocyanic acid, and is prepared by the process mentioned 
above, being afterwards diluted with water to the proper strength. 
Scheele's acid varies in strength, but usually contains between 4 and 5 per 
cent, of hydrocyanic acid. This acid is prepared from Prussian blue 
by the process originally employed by Scheele when the acid was dis- 
covered. It consists in boiling Prussian blue with water and red oxide 
of mercury until the blue colour disappears ; ferric oxide is separated, and 
mercuric cyanide (HgCy 2 ) passes into solution ; the latter is filtered, 
mixed with diluted sulphuric acid, and shaken with iron filings, which 
precipitate the mercury in the metallic state, leaving free hydrocyanic acid 
in the liquid, which is then distilled — 

HgCy 2 + Fe + H 2 S0 4 - 2HCy + FeS0 4 + Hg. 

In order clearly to understand this process, it must be known that the 
mercury exhibits a special tendency to combine with cyanogen, which is 
sufficiently powerful, in this instance, to bring about the decomposition 
of the ferrocyanogen existing in the Prussian blue, a part of the cyanogen 
being exchanged for the oxygen of the mercuric oxide. 

It is from the cyanide of mercury that the pure anhydrous hydrocyanic 



PEEPARATION OF CYANOGEN. 443 

acid and cyanogen itself are prepared. For these purposes, it may be 
obtained by dissolving the red oxide of mercury in hydrocyanic acid, 
when a double decomposition takes place, exactly as with hydrochloric 
acid, HgO + 2HCy = HgCy 2 + H 2 0, and the mercuric cyanide is obtained 
in square prismatic crystals on evaporating the solution. If these crystals 
be dried and gently warmed with strong hydrochloric acid, mercuric 
chloride will be formed, and hydrocyanic acid evolved, HgCy 2 + 2HCl 
= HgCl 2 + 2HCy. The mixed vapours of hydrochloric and hydrocyanic 
acid are passed over fragments of marble (CaC0 3 ), which absorb the 
hydrochloric acid (CaC0 3 + 2HCl = CaCl 2 + H 2 + C0 2 ), but not the 
hydrocyanic, since the latter is too weak an acid even to displace carbonic 
acid. The mixture of hydrocyanic acid and carbon dioxide is passed over 
calcium chloride to remove aqueous vapour, and afterwards through a 
tube cooled in a mixture of ice and salt, when the hydrocyanic acid is 
condensed to a colourless liquid, which evaporates so rapidly when exposed 
to the air that it lowers the temperature to the freezing-point of the acid, 
which is about 0° F. ; at a little above the ordinary temperature (79° F.) 
it boils, and emits a vapour which burns with a blue flame. When kept 
for some time it is liable to undergo spontaneous decomposition, evolving 
ammonia, and being converted into a brown mass of uncertain composition. 
The aqueous solution of the acid suffers a similar change, and since 
exposure to light favours the decomposition, the medicinal acid is usually 
kept in bottles covered with paper. The presence of a very small quantity 
of sulphuric acid prevents this change, and hence the acid prepared by 
distilling ferrocyanide of potassium with sulphuric acid, which usually 
contains traces of the latter, can be preserved much better than that 
prepared by other methods. 

Among the products of decomposition is a crystalline solid body having the same 
percentage composition as the acid itself, and believed to be H 3 C 3 N 3 . 

By passing HC1 gas into HON mixed with acetic ether cooled in ice and salt, a 
colourless crystalline compound, 2HCN.3HC1, is obtained. It is insoluble in ether 
and in acetic ether, and is decomposed by water, yielding formic acid and ammonium 
chloride. Alcohol also decomposes it with production of hydric chloride, ethyle 
chloride, ammonium chloride, formic ether, and the hydrochlorate of a base termed 
jormamidine HC.N 2 H 3 , which might evidently be formulated as formyldiamine 
or two molecules of ammonia with triatomic formyle in place of 3 atoms of hydrogen. 

When hydriodic acid gas is passed into anhydrous hydrocyanic acid cooled by ice, 
a crystalline body is formed, which has the composition HCN.HI. It is readily 
soluble in water and alcohol, but not in ether, and may be sublimed with little 
decomposition. This substance is not acid, and does not answer to the tests for 
hydrocyanic acid. When decomposed by potash, it gives ammonia, potassium 
formiate, and potassium iodide, so that it may be regarded as the hydriodate of an 
ammonia formed by the substitution of 1 molecule of the triatomic radical formyle 
(CH) for the 3 atoms of hydrogen ; or formylamine hydriodate N(CH)'".HI. 

When hydrocyanic acid is acted on by nascent hydrogen (zinc and sulphuric acid) 
it yields methylamine, HCN + H 4 = NH 2 CH 3 . 

317. Cyanogen* itself (CN) 2 can be prepared by the mere action of 
heat upon the cyanide of mercury (in a test-tube provided with a glass 
jet for burning the gas, fig. 280). This salt resolves itself into metallic 
mercury, cyanogen, and a brown substance which has been called para- 
cyanogen (C 4 N 4 ), and appears to have been formed by the union of four 
atoms of cyanogen. Cyanogen gas is easily distinguished from all others 

* Cyanogen appears to be produced by direct combination of carbon with nitrogen at the 
high temperature of the electric light. 




444 CYANIDE OF POTASSIUM. 

by its peculiar odour and its property of burning witb a pink flame edged 
with green. Being nearly twice as heavy as air (sp. gr. 1 *8), it may be 
collected by downward displacement, for water dissolves about four times 
its volume of the gas, yielding a solution which 
is prone to undergo a spontaneous decomposition 
remarkable for the comparatively complex pro- 
ducts which it furnishes, amongst which we trace 
the oxalate (NH 4 ) 2 C 2 4 and formiate(NH 4 CH0 2 ) 
of ammonium, and urea (CH 4 N 2 0), all derived, 
be it remembered, from the elements of cyanogen 
and water. In its chemical relations, cyanogen 
presents a striking resemblance to chlorine. 
Thus, at a slightly elevated temperature, potas- 
sium and sodium take fire in it, forming the 
Fig. 280. cyanides of those metals, precisely as the chlorides 

would be formed. Again, when cyanogen is 
absorbed by a solution of potash, the cyanide and cyanate of potassium 
are formed — 

2KHO + Cy 2 = KCyO {Potassium cyanate) + KCy {Potassium cyanide) + H 9 0, 

just as the chloride and hypochlorite of potassium result from the action 
of chlorine upon potash, 2K HO + Cl 2 = KCIO + KC1 + H 2 0. A pressure 
of about 4 atmospheres is required to liquefy cyanogen, when it forms 
a colourless liquid of sp. gr. 0*87, freezing to a crystalline mass at 
- 30° F. 

Cyanide of potassium. — The most useful of the cyanides is potassium 
cyanide, which is extensively employed in electro-plating and gilding. 

This salt may be formed by a very interesting process, which is one of 
the few in which the atmospheric nitrogen takes part, and consists in 
passing air over red hot charcoal which has been previously soaked in a 
strong solution of potassium carbonate and dried, when the nitrogen 
requisite for the formation of the cyanide is absorbed from the air, and 
carbonic oxide is disengaged ; K 2 C0 3 + C 4 + N 2 = 2KCN + 3CO. 

It is probably by a similar change that the potassium cyanide is 
produced in blast-furnaces (page 304) in which iron ores are reduced, 
the potash being derived from the ash of the fuel. The cyanide is always 
prepared for use from the ferrocyanide, which is resolved by a very high 
temperature into potassium cyanide and iron carbide, with evolution 
of nitrogen ; K 4 CygFe = 4KCy + FeC 2 + N 2 . 

In order to avoid the loss of the 2 atoms of cyanogen, it is usual 
to fuse the ferrocyanide with potassium carbonate in the proportion of 3 
parts of the dry carbonate to 7 parts of the dried ferrocyanide ; the 
mixture is fused in a covered earthen crucible, and occasionally stirred 
until gas ceases to be evolved ; the crucible is then removed from the fire, 
allowed to stand for a minute or two that the metallic iron may subside, 
and the clear fused cyanide poured out on to a stone. The change involved 
in this process is represented by the following equation — 

K 4 Cy 6 Fe + K 2 C0 3 = 5KCy + KCyO + Fe + C0 2 , 

whence it will be seen that the commercial potassium cyanide is contami- 
nated with cyanate. It also contains a considerable quantity of carbonate, 
so that the proportion of cyanide is often only 60 per cent. The white 



CYANIDE OF POTASSIUM. 445 

porcelain-like masses of potassium cyanide deliquesce when exposed to 
the air, and emit the odour of hydrocyanic acid as well as that of 
ammonia ; the former is disengaged from the cyanide by the action of 
the atmospheric carbonic acid, whilst the ammoniacal odour is due to the 
ammonium carbonate produced by the action of moisture upon the 
cyanate ; 2KCJSTO + 4H 2 = K 2 C0 3 + (NH 4 ) 2 C0 3 . 

Pure potassium cyanide is deposited in colourless cubical crystals when 
vapour of hydrocyanic acid is passed into an alcoholic solution of potash, 
or it may be obtained by boiling the commercial cyanide with alcohol 
and filtering while hot, when the cyanide crystallises out as the solution 
cools. 

The use of potassium cyanide in electro-plating and gilding depends 
upon the power of a solution of the salt to dissolve the cyanides of gold 
and silver, forming compounds which are easily decomposed by the 
galvanic current, with deposition of metallic gold or silver upon any 
object capable of conducting the current, which may be attached to the 
negative pole (page 380). Solution of potassium cyanide is also able 
to dissolve metallic silver, chloride, iodide, and sulphide of silver, which 
is taken advantage of in fixing photographic images, and in cleaning 
silver or gold lace. 

At a high temperature, potassium cyanide is a very powerful reducing 
agent, abstracting an atom of oxygen from most of the metallic oxides, 
so as to liberate the metals, being itself converted into potassium cyanate. 
Thus, when the stannic oxide is fused with potassium cyanide Sn0 2 
+ 2KCy = Sn + 2KCyO. This property of the cyanide is often applied 
in chemical experiments. The cyanate is readily distinguished by the 
peculiar pungent odour of cyanic acid, which it emits when treated with 
dilute sulphuric acid, though the greater part of the cyanic acid is 
decomposed with effervescence, yielding ammonium sulphate and carbonic 
acid gas — 

2KCNO + 2H 2 S0 4 + 2H 2 = K 2 S0 4 + CN"H 4 ) 2 S0 4 + 2C0 2 . 

The following process, for the preparation of potassium cyanate, published by C. A. 
Bell, is very satisfactory : 4 parts of perfectly dried potassium ferrocyanide are in- 
timately mixed with 3 parts of potassium bichromate ; the mixture is thrown, in small 
portions, into a porcelain or iron dish heated sufficiently to kindle it. When the 
whole has smouldered and blackened, it is allowed to cool, introduced into a flask, 
boiled with strong methylated alcohol and filtered ; the potassium cyanate crystallises 
out on cooling. 

When fused potassium cyanate is triturated with dried oxalic acid, and 
the mass treated with water, a white insoluble substance is left, which has 
been called cyamelide, and has the composition CHNO, being metameric 
with cyanic acid, HCNO ; when this substance is distilled, cyanic acid 
passes over as a colourless liquid, which can only be preserved at a very 
low temperature, for if the receiver containing it be removed from the 
freezing mixture employed to condense the cyanic acid, the latter becomes 
hot and turbid, soon begins to boil violently, and is converted into a 
white mass of cyamelide resembling porcelain. 

Potassium cyanide, when fused with sulphur, forms a compound cor- 
responding to potassium cyanate, but containing sulphur in place of 
oxygen, and having the formula KCyS, which is commonly spoken of as 
potassium sulphocyanide, being represented as containing a compound 
radical, sulphocymiogen CyS = Scy. The potassium sulphocyanide is 



446 RED PRUSSIATE OF POTASH. 

generally prepared by fusing 3 parts of dried potassium ferrocyanide and 
1 part of potassium carbonate (the materials for making potassium cyanide) 
with 2 parts of sulphur in a covered crucible. By washing the cooled 
mass with boiling water, the sulphocyanide is extracted, and may be 
obtained, by evaporating the solution, in prismatic crystals resembling 
nitre. By decomposing the potassium sulphocyanide with lead acetate, the 
lead sulphocyanide (Pb(CyS) 2 ) is obtained, and this, when acted upon with 
sulphuretted hydrogen, yields lead sulphide and hydrosulphocyanic acid, 
HCyS, the latter being a colourless oily liquid which may be crystallised 
by cold. This acid is remarkable for the dark red colour (due to ferric 
sulphocyanide) which it gives with ferric salts, for which potassium 
sulphocyanide is frequently employed as a test. A very delicate test 
(Liebig's test) for hydrocyanic acid, in cases of poisoning, is also founded 
upon that circumstance, for if a watch-glass moistened with yellow 
ammonium sulphide (page 271) be exposed to the action of vapour of 
hydrocyanic acid, the latter is absorbed and converted into ammonium 
sulphocyanide — 

(XH 4 ) 2 S + S 2 + 2HCy = 2NH 4 CyS + H 2 S , 
by applying a gentle heat to the watch-glass, any excess of ammonium 
sulphide is volatilised, and a drop of ferric chloride will then give the 
blood-red colour with the sulphocyanide. 

By covering potassium cyanide with water in a flask, and saturating with hydro- 
sulphuric acid, Wallace obtained a yellow substance, sparingly soluble in water, which 
he terms chrysean. It appears to have the formula C 4 H 5 N 3 S 2 , and to be formed by 
the. reaction 4KCN + 5 H. 2 S = 2 £ 2 S + NH 4 HS + C 4 H 5 N 3 S. 2 . Chrysean crystallises from 
boiling water in golden needles. It dissolves in alcohol, ether, acids, and alkalies, 
crystallising out unchanged. Its alcoholic solution has a tine red colour, and changes 
to a fugitive green on adding a little alkali. 

Solution of potassium cyanide dissolves iodine readily, and if the solution be gently 
warmed, fine needles of cyanogen iodide, CNI, condense on the cool sides of the vessel. 

318. Ferricyanide of potassium. — When chlorine is passed into a solu- 
tion of potassium ferrocyanide, the liquid assumes a brown colour, and, 
when evaporated, deposits beautiful red rhombic prisms, which are found, 
on analysis, to have the composition K 3 Cy 6 Fe, having been formed from 
the ferrocyanide according to the equation — 

. K 4 Cy 6 Fe {Ferrocyanide) + CI = K 3 Cy 6 Fe {Ferricyanide) + KC1 . 

This salt is known as red prussiate of potash, or potassium ferricyanide, 
and is used in dyeing ; for if a piece of stuff be heated in a solution of 
the ferricyanide acidulated with acetic acid, a blue compound similar to 
Prussian blue is deposited in the fibre. 

Potassium ferricyanide is also employed for the preparation of TurribulVs 
blue (ferrous ferricyanide), which is precipitated when a solution of that 
salt is mixed with one of ferrous sulphate — 

3FeS0 4 + 2K 3 (Cy 6 Fe) = 3K 2 S0 4 + Fe 3 (Cy 6 Fe) 2 .* 

In calico-printing, a mixture of potassium ferricyanide with potash is 
employed as a discharge for indigo, such a mixture acting as a powerful 
bleaching agent, in consequence of its tendency to impart oxygen to any 
substance in need of that element, the ferricyanide being converted into 
the ferrocyanide ; thus — 

2K 3 (Cy 6 Fe) {Ferricyanide) + 2KHO p 2K 4 (Cy 6 Fe) {Ferrocyanide) + + H 2 0. 

* It has been stated that this precipitate is really the ferroso-ferric ferrocyanide 
Fe'Te/'Fcyc, . . 



CHLORIDES OF CYANOGEN. 447 

The f erricyanide is assumed to contain a compound radical ferricyanogen 
(Cy 6 Fe), which differs from ferrocyanogen in containing triatomic iron 
Fe'", instead of diatomic iron, Fe". The formula Cy 6 'Fe"' shows that 
this radical must be triatomic and not tetratomic like Cy 6 'Fe". The 
hydroferricyanic acid (H 3 Cy 6 Fe) can be obtained in a crystallised state, 
and many of the corresponding ferric} 7 anides have been examined. 

Ferrocyanogen and ferricyanogen are not the only compound radicals 
of this description ; there are cobalticyanogen (Cy 6 Co), manganicyanogen 
(Cy 6 Mn), chroma cyanogen (Cy 6 Cr) and chromicyanogen (Cy 6 Cr), platino- 
cyanogen (Cy 4 Pt), palladiocyanogen (Cy 4 Pd), and iridiocyanogen (Cyjr), 
but none of these have received any useful applications. The platino- 
cyanides are remarkable for their brilliant colours. 

319. CMorides of cyanogen. — When moist mercuric cyanide is shaken 
up in a bottle of chlorine gas, and set aside for some time in a dark place, 
the yellow colour of the chlorine disappears, and the bottle is filled with 
a colourless gas having a remarkably pungent and tear-exciting odour ; this 
is the gaseous cyanogen chloride (CyCl) ; HgCy 2 + Cl 4 = HgCl 2 + 2CyCl. 
If light have access during this experiment, an oily liquid chloride, 
Cy 2 Cl 2 , is produced. 

The cyanogen chloride gas may by liquefied by a pressure of four 
atmospheres, and if the liquid is kept for some days in a sealed tube, it is 
converted into a white mass of solid cyanogen chloride, Cy 3 Cl 3 . When 
this is acted on by water, it yields cyanuric acid, H 3 Cy 3 3 , according 
to the equation Cy 3 Cl 3 + 3H 2 = 3HC1 + H 3 Cy 3 3 . This acid is very 
interesting on account of its polymeric relation to cyanic acid (HCyO), 
which may be obtained from it by distillation. It is a tribasic acid, and 
forms, like tribasic phosphoric acid (page 231), three series of salts, having 
the formulae, respectively, M' 3 Cy 3 3 , M' 2 HCy 3 8 , M'H 2 Cy 3 3 . 

The phosphorous cyanide, PCy 3 , has been sublimed in tabular crystals 
from a mixture of silver cyanide and phosphorous chloride heated in a 
sealed tube to 280° F. for some hours, and afterwards distilled in a 
current of dry carboni cacid gas. Phosphorous cyanide inflames at a very low 
temperature, and is decomposed by water, yielding cyanic and phosphorous 
acids. 

320. Nitroprussides. — When potassium ferrocyanide is boiled with dilute nitric 
acid, a point is attained at which the solution gives a slate-coloured precipitate with 
ferrous sulphate ; if it be then boiled with an excess of sodium carbonate, filtered, 
and evaporated, it deposits ruby-red prismatic crystals of sodium nitroprusside 
(ISra 4 Cy 10 N 2 O 3 Fe. 2 . 4 A(p ), from which the nitroprussides of other metals may be 
obtained. 

The hydronitroprussic acid (H 4 Cy 10 N 2 O 3 Fe 2 .2Aq.) has also been prepared and 
crystallised. 

The nitroprussides were found by Hadow to be formed from a double molecule 
of the ferricyanides by the exchange of a molecule of cyanogen for a molecule of 
nitrous anhydride (N" 2 3 ), and the simultaneous removal of 2 atoms of the metal with 
which the ferricyanogen was combined. Thus the double molecule of potassium 
f erricyanide, K 6 Cy 12 Fe 2 , becomes nitroprusside of potassium, K 4 Cy 10 N 2 O 3 Fe 2 , when 
boiled with nitric acid, other products being formed at the same time by the oxidising 
action of the nitric acid. 

Based upon this view of its constitution, a more certain and economical process 
for the production of sodium nitroprusside was devised by Hadow, which consists 
in acting upon the potassium ferricyanide with sodium nitrite, acetic acid, and 
mercuric chloride, when the mercury removes a molecule of cyanogen, and the chlorine 
-2 atoms of potassium, the nitrite acting on the residue of the ferricyanide, and con- 
verting it into nitroprusside, which, by double decomposition with the sodium acetate, 



448 PREPARATION OF FULMINATE OF MERCURY. 

yields potassium acetate and sodium nitroprusside. The mercuric cyanide crystallises 
out first, and the sodium nitroprusside may be obtained in crystals from the evapo- 
rated solution. 

The more recent researches of Stadeler have still further simplified the constitution 
of the nitroprussides. By the action of potassium cyanide upon ferrous sulphate, 
he obtained an orange precipitate composed of KFe 2 "Cy 5 , in which 2 atoms of 
diatomic iron have replaced 4 atoms of monatomic potassium in 5 molecules of the 
cyanide ; 5KCy + 2Fe"S0 4 = KFe 2 "Cy 5 + 2K 2 S0 4 . 

When this precipitate was treated with potassium nitrite, it furnished the nitro- 
prusside ; K'Fe 2 "Cy 5 ' + KN0 2 = K 2 'Fe"(N0yCy g + FeO. 

According to this, the hypothetical radical of the nitroprussides would contain 
Cy s (NO)'Fe", representing ferrocyanogen Cy 6 Fe" in which (NO)' has replaced Cy'. 
The monatomic character of the NO is shown in potassium nitrite KN0 2 or K'(NO)'6". 
It will be observed that Stadeler's formula for the nitroprussides differs from Hadow's 
only by a single atom of oxygen in Hadow's molecule, thus — 

Double molecule of potassium nitroprusside (Stadeler), K 4 Fe 2 N. 2 O 2 Cy 10 , 
Potassium nitroprusside (Hadow), K 4 Fe 2 N 2 O 3 Cy ]0 

so that whereas Hadow believed in the substitution of nitrous anhydride (N 2 3 ) for a 
part of the cyanogen, Stadeler finds that it is really NO, the radical of the nitrous 
anhydride ((NO)'(NO)'0") which replaces the cyanogen.* 

On the latter view, the diatomic character of the assumed radical Cy 5 '(NO)' Fe" is 
at once explained, for it evidently requires 2 atoms of potassium to complete the 
saturation of the Cy 5 . 

The sodium nitroprusside is used as a test for the alkaline sulphides, with a very 
slight trace of which it gives a magnificent purple colour. Thus, an inch or two of 
human hair, fused with sodium carbonate before the blowpipe, will yield sufficient 
sodium sulphide to strike a purple tint with the nitroprusside. 

321. The Fulminates. — The violently explosive compound known as 
fulminate of mercury, which is so largely employed for the manufacture 
of percussion caps, is connected with the series of cyanogen compounds. 

Preparation of fulminate of mercury. — This substance is prepared by 
the action of alcohol upon a solution of mercury in excess of nitric acid ; 
and as this action is of a violent character, some care is necessary in order 
to avoid an explosion. On a small scale, the fulminate may be obtained 
without any risk by strictly attending to the following prescription : — 

Weigh out, in a watch-glass, 25 grains of mercurj-, transfer it to a half-pint beaker, 
add half an ounce (measured) of ordinary concentrated nitric acid (sp. gr. 1*42), and 
apply a gentle heat. As soon as the last particle of mercury is dissolved, place the 
beaker upon the table, away from any flame, and pour into it, pretty quickly, at 
arm's length, 5 measured drachms of alcohol (sp. gr. 0'87). Very brisk action will 
ensue, and the solution will become turbid from the separation of crystals of the 
fulminate, at the same time evolving very dense white clouds, which have an agree- 
able odour, due to the presence of nitrous ether, aldel^de, and other products of the 
action of nitric acid upon alcohol. The heavy character of these clouds is caused by 
the presence of mercury, though in what form has not been ascertained ; much nitrous 
oxide and hydrocyanic acid are evolved at the same time. When the action has 
subsided, the beaker may be filled with water, the fulminate allowed to settle, and the 
acid liquid poured off. The fulminate is then collected on a filter, washed with water 
as long as the washings taste acid, and dried by exposure to air. 

On a large scale, the preparation of mercuric fulminate is carried out in the open air, 
under sheds. At Montreuil, 300 grammes of mercury are dissolved in 3 kilogrammes 
of colourless nitric acid of sp. gr. 1 '4, in the cold. The solution is transferred to a 
retort, and 2 litres of strong alcohol are added. In summer no heat is applied, and 
the vapours are condensed in a receiver and added to a fresh charge. 

When the action has ceased, the contents of the retort are poured into a shallow pan, 
and when cold, the fulminate is collected in a conical earthen vessel partially plugged 
at the narrow end. It is washed with rain water, and drained until it contains 20 per 
cent, of water, being stored in that state. 

* Stadeler's view is confirmed by the recent analyses of certain nitroprussides by 
Bernheimer. 



MANUFACTURE OF PERCUSSION CAPS. 449 

Mercuric fulminate is represented by the formula HgC 2 N 2 2 , being 
derived from the hypothetical fulminic acid, H 2 C 2 N 2 2 , by the substitu- 
tion of Hg" for H 2 . 

Its production by the action of nitric acid upon mercury and alcohol 
may be explained by the following reactions : — ■ 

(1) Mercury, dissolved . in nitric acid, yields mercuric nitrate and 
nitrous acid ; 3HN0 3 + Hg = Hg(N0 3 ) 2 + HN0 2 + H 2 0. 

(2) Nitrous acid, acting upon alcohol (ethyle hydrate), gives nitrous 
ether (ethyle nitrite) and water ; C 2 H 5 .OH + HN0 2 = C 2 H 5 .N0 2 + H 2 0. 

(3) Ethyle nitrite, acted on by another molecule of nitrous acid, gives 
f ulminic acid and water ; C 2 H 5 N0 2 + HN0 2 = H 2 C 2 N" 2 2 + 2H 2 . 

(4) Mercuric nitrate (formed in the first reaction) may be supposed to 
act upon the fulminic acid, producing mercuric fulminate and nitric acid ; 
Hg(N0 3 ) 2 + H 2 C 2 N 2 2 = HgC 2 N 2 2 + 2HN0 3 . 

Properties of mercuric fulminate. — This substance is deposited in 
the above process in fine needle-like crystals, which often have a grey 
colour from the accidental presence of a little metallic mercury. It may 
be purified by boiling it with water, in which it is sparingly soluble, and 
allowing the fulminate to crystallise from the filtered solution. Very 
moderate friction or percussion will cause it to detonate violently, so that 
it must be kept in a corked bottle lest it should be exploded between the 
neck and the stopper. It is usually preserved in a wet state, with about 
one-fifth its weight of water. Its explosion is attended with a bright 
flash, and with grey fumes of metallic mercury. The equation which 
represents the decomposition is HgC 2 N 2 2 = Hg + 2CO + N 2 ; and its 
violence must be attributed to the sudden evolution of a large volume of 
gas and vapour from a small volume of solid, for the fulminate, being 
exceedingly heavy (sp. gr. 4"4), occupies a very small space when com- 
pared with the gaseous products of its decomposition, especially when the 
latter are expanded by the heat. One gramme of fulminate evolves 403 '5 
units of heat, giving an estimated maximum pressure of 48,000 atmo- 
spheres. The evolution of heat during the explosion, apparently in 
contradiction to the rule that heat is absorbed in decomposition, must be 
ascribed to the circumstance that the heat evolved by the oxidation of 
the carbon exceeds that absorbed in the decomposition of the fulminate. 
A temperature of 195° C. explodes fulminate of mercury, and the same 
result is brought about by touching it with a glass rod dipped in concen- 
trated sulphuric or nitric acid. The electric spark, of course, explodes it. 

Cap composition. — The explosion of mercuric fulminate is so violent 
and rapid that it is necessary to moderate it for percussion caps. For 
this purpose it is mixed with potassium nitrate or chlorate, the oxidising 
property of these salts possibly causing them to be preferred to any merely 
inactive substances, since it would tend to increase the temperature of the 
flash by burning the carbonic oxide into carbon dioxide, and would thus 
ensure the ignition of the cartridge. For military caps, in this country, 
potassium chlorate is always mixed with the fulminate, and powdered 
glass is sometimes added to increase the sensibility of the mixture to 
explosion by percussion. Antimony sulphide is sometimes substituted for 
powdered glass, apparently for the purpose of lengthening the flash by 
taking advantage of the powerful oxidising action of potassium chlorate 
upon that compound (page 165). Since the composition is very liable to 
explode under friction, it is made in small quantities at a time, and with- 

2.F 



450 PREPARATION OF FULMINATE OF SILVER. 

out contact with any hard substance. After a little of the composition 
has been introduced into the cap, it is made to adhere and waterproofed 
by a drop of solution of shellac in spirit of wine. 

If a thin train of mercuric fulminate be laid upon a plate, and covered, except a 
little at one end, with gunpowder, it will be found, on touching the fulminate Avith a 
hot wire, that its explosion scatters the gunpowder, but does not inflame it. On 
repeating the experiment with a mixture of 10 grains of the fulminate and 15 grains 
of potassium chlorate, made upon paper with a card, the explosion will be found to 
inflame the gunpowder. 

By sprinkling a thin layer of the fulminate upon a glass plate, and firing it with a 
hot wire, the separated mercury may be made to coat the glass, so as to give it all the 
appearance of a looking-glass. 

Although the effect produced by the explosion of mercuric fulminate 
is very violent in its immediate neighbourhood, it is very slightly felt at 
a distance, and the sudden expansion of the gas will burst fire-arms, 
because it does not allow time for overcoming the inertia of the ball, 
though, if the barrel escape destruction, the projectile effect of the fulmi- 
nate is found inferior to that of powder. It has been proved by experi- 
ment, that the mean pressure exerted by the explosion of mercuric 
fulminate is very much lower than that produced by gun-cotton, and 
only f ths of that produced by nitroglycerine. Its great pressure is due 
to its instantaneous decomposition into CO, N and Hg vapour within a 
space not sensibly greater than the volume of the fulminate itself, which 
volume being very small, on account of the high density of the fulminate, 
the escaping gases exert an enormous pressure at the moment of explosion. 
This detonating property of mercuric fulminate renders it exceedingly 
useful for effecting the detonation of gun-cotton and nitroglycerine. 
Berthelot finds that even such stable gases as acetylene, cyanogen, and 
nitric oxide are decomposed into their elements by the detonation of 
mercuric fulminate. 

Mercuric fulminate is generally contaminated with mercuric oxalate 
(HgC 2 4 ), which is one of the secondary products formed during its 
preparation. 

Fulminate of silver, Ag 2 C 2 N 2 2 , is prepared by a process very similar 
to that for fulminate of mercury ; but since its explosive properties are far' 
more violent, it is not advisable to prepare so large a quantity. Ten grains 
of pure silver are dissolved, at a gentle heat, in 70 minims of ordinary 
concentrated nitric acid (sp. gr. 1*42) and 50 minims of water. As soon 
as the silver is dissolved, the lamp is removed, and 200 minims of alcohol 
(sp. gr. 0*87) are added. If the action does not commence after a short 
time, a very gentle heat may be applied until effervescence begins, when 
the fulminate of silver will be deposited in minute needles, and may be 
further treated as in the case of fulminate of mercury.' 55 ' Silver fulminate 
is also produced when nitrous anhydride is passed into an alcoholic solu- 
tion of silver nitrate. When dry, the fulminate must be handled with 
the greatest caution, since it is exploded far more easily than the mercury 
salt ; it should be kept in small quantities, wrapped up separately in paper, 
and placed in a card-board box. Nothing harder than paper should be 
employed in manipulating it. The violence of its explosion renders it 

* If the nitric acid and alcohol are not of the exact strength here prescribed, it may be 
somewhat difficult to start the action unless two or three drops of red nitric acid (contain- 
ing nitrous acid) are added. Standard silver (containing copper) may be used for preparing 
the fulminate. 



CHEMICAL CONSTITUTION OF THE FULMINATES. 451 

useless for percussion caps, but it is employed in detonating crackers. 
Silver fulminate is sparingly soluble in cold water, but dissolves in 36 
parts of boiling water. 

If a minute particle of the fulminate be placed upon a piece of quartz, and gently 
pressed with, the angle of another piece, it will explode with a flash and smart report. 

A throw-down detonating cracker may be made by screwing up a particle of silver 
fulminate in a piece of thin paper, with some fragments obtained by crushing a 
common quartz pebble. 

The explosion of silver fulminate may be compared with that of the mercury salt, 
by heating small equal quantities upon thin copper or platinum foil, when the fulminate 
of mercury will explode with a slight puff, and will not injure the foil, but that of 
silver will give a loud crack and rend a hole in the metal. 

If a particle of silver fulminate be placed upon a glass plate and touched with a 
glass rod dipped in oil of vitriol, it will detonate and leave a deposit of silver upon the 
glass. 

"When silver fulminate (Ag 2 C 2 N" 2 2 ) is dissolved in warm ammonia, 
the solution deposits, on cooling, crystals of a double fulminate of silver 
and ammonium, Ag(XH 4 )C 2 N 2 2 , which is even more violently explosive, 
and is dangerous while still moist. A similar compound is formed with 
mercuric fulminate. 

On adding potassium chloride in excess to silver fulminate, only half 
the silver is removed as chloride, and the double fulminate of silver and 
potassium, AgKC 2 N" 2 2 , may be crystallised from the solution. By 
the careful addition of nitric acid, the K may be replaced by H, and the 
acid silver fulminate, AgHC 2 N 2 2 , obtained, which is easily soluble in 
boiling water, and c^stallises out on cooling ; by boiling with silver oxide, 
it is converted into the normal fulminate. 

Various other fulminates and double fulminates have been obtained. 
They are all explosive. 

Chemical constitution of the fulminates. — The fact of the existence of 
double fulminates and acid fulminates renders it necessary to write the 
formula of silver fulminate, for example, Ag 2 C 2 N 2 2 , instead of AgCXO, 
in order to show that half of the silver is capable of being exchanged for 
another metal or for hydrogen. It will be seen that this formula would 
also represent 2 molecules of silver cyanate (AgCXO), but the properties 
of this salt are entirely different from those of the fulminate. That a 
strong connexion exists, however, between the fulminates and the 
cyanogen compounds, is shown by several reactions. Thus, if mercuric 
fulminate be heated with hydrochloric acid, it is dissolved with evolu- 
tion of a powerful odour of hydrocyanic acid, whilst mercuric chloride 
and oxalate, with ammonium chloride, remain in the solution. Again, if 
an excess of silver fulminate be acted on by hydrosulphuric acid, cyanic 
acid may be obtained in solution, and becomes converted into hydrosulpho- 
cyanic acid, when the hydrosulphuric acid is in excess. By decomposing 
the double fulminate of copper and ammonium (Cu(XH 4 ) 2 (C 2 X 2 2 ) 2 ) 
with hydrosulphuric acid, there are produced, hydrosuljDhocyanic acid and 
urea, the latter having the same composition as ammonium cyanate — 

Cu(XH 4 ) 2 (C 2 N 2 2 ) 2 + 3H 2 S = CuS + 2H 2 + 2HCNS + 2CH 4 N 2 



Hydrosulpho- 



Urea. 



cyanic acid. 

These reactions have induced many chemists to regard the fulminates 
as compounds derived from an acid having the composition H 2 Cy 2 2 , 
intermediate in composition between cyanic acid (HCyO) and cyanuric 



452 PRODUCTS FROM COAL. 

acid (H 3 Cy 3 3 ), but the f ulrninic acid has not yet been obtained in a 
separate form. The formula C iv Hg"Cy'(N0 2 )' agrees better with modern 
researches. 

Mercuric fulminate dissolves when boiled with solution of potassium chloride, and 
the solution, when evaporated, yields crystals of potassium fulminurate or isocyanurate, 
KC 3 N 3 H. 2 3 , which has the same percentage composition as acid potassium cyanurate 
KH 2 Cy 3 3 , but the acid contained in the fulminurate forms only one series of 
salts, and is therefore monobasic. The fulminurates are feebly explosive. The 
production of fulminuric acid from the hypothetical fulminic acid may be represented 
by the equation 2(H 2 C 2 N 2 2 ) + H 20 = C0 2 + NH 3 + H C 3 N 3 H 2 3 . 

PKODUCTS OF THE DESTRUCTIVE DISTILLATION 
OF COAL. 

322. Much of the extraordinary progress made by chemistry during 
the last half century must be attributed to the introduction and great 
extension of the manufacture of coal gas. No other branch of manufac- 
ture has brought into notice so many compounds not previously obtained 
from any other source, and, above all, offering, at first sight, so very 
little promise of utility, as to press urgently upon the chemist the necessity 
for submitting them to investigation. 

Although many important additions to chemical knowledge have re- 
sulted from the labours of those who have engaged in devising the best 
methods of obtaining the coal gas itself in the state best fitted for con- 
sumption, far more benefit has accrued to the science from investigations 
into the nature of the secondary products of the manufacture, the removal 
of which was the object to be attained in the purification of the gas. 

Of the compounds of carbon and hydrogen, very little was known pre- 
viously to the introduction of coal gas ; and although the liquid hydro- 
carbons composing coal-naphtha were originally obtained from other 
sources, the investigation of their chemical properties has been greatly 
promoted by the facility with which they may be obtained in large quan- 
tities from that liquid. The most important of these hydrocarbons, 
benzole or benzene, was originally procured from benzoic acid; but it would 
have been impossible for it to have fulfilled its present useful purposes,' 
unless it had been obtained in abundance as a secondary product in the 
manufacture of coal gas ; for, leaving out of consideration the various uses 
to which benzene itself is devoted, it yields the nitrobenzene, so much 
used in perfumery, and from this we obtain aniline, from which many 
of the most beautiful dyes are now prepared. 

The naphthalene found so abundantly in coal-tar possesses a peculiar 
interest, as having formed the subject of the beautiful researches by which 
Laurent was led to propose the doctrine of substitution, which has since 
thrown so much light upon the constitution of organic substances. 

We are also especially indebted to coal-tar for our acquaintance with the 
very interesting and rapidly extending class of volatile alkalies, of which 
the above-mentioned aniline is the chief representative, and for phenic or 
carbolic acid, from which are derived the large number of substances com- 
posing the phenyle-series. 

The retorts in which the distillation of coal is effected are made either 
of cast-iron or of stoneware, generally having the form of a flattened 
cylinder, and arranged in sets of three or five, heated by the same coal fire 
fig. 281), The charge for each 'retort is about two bushels, and is thrown 



MANUFACTURE OF COAL GAS. 



453 



on to the red hot floor of the retort, as soon as the coke from the previous 
distillation has been raked out ; the mouth of the retort is then closed 
with an iron plate luted with clay. An iron pipe rises from the upper 
side of the front of the retort projecting from the furnace, and is curved 
round at the upper extremity, which passes into the side of a much wider 
tube, called the hydraulic main, running above the furnaces, at right 
angles to the retorts, and receiving the tubes from all of them. This tube 
is always kept half full of the tar and water which condense from the gas, 
and below the surface of this liquid the delivery tubes from the retorts 
are allowed to dip, so that although the gas can bubble freely through the 
liquid as it issues from the retort, none can return through the tube whilst 
the retort is open for the introduction of a fresh charge. 




The aqueous portion of the liquid deposited in the hydraulic main is 
known as the ammoniacal liquor, from its consisting chiefly of a solution 
of various salts of ammonium, the chief of which is the carbonate ; 
sulphide, cyanide, and sulphocyanide of ammonium are also found in it. 

From the hydraulic main the gas passes into the condenser, which is 
composed of a series of bent iron tubes kept cool either by the large sur- 
face which they expose to the air, or sometimes by a stream of cold 
water. In these are deposited, in addition to water, any of the volatile 
hydrocarbons and ammonium salts which may have escaped condensation 
in the hydraulic main. Even in the condenser the removal of the 
ammoniacal salts is not complete, so that it is usually necessary to pass the 
gas through a scrubber or case containing fragments of coke, over which 
a stream of water is allowed to trickle, in order to absorb the remaining 
ammoniacal vapours. 

The tar which condenses in the hydraulic main is a very complex 
mixture, of which the following are some of the leading components : — 



454 



PURIFICATION OF COAL GAS. 





Boiling-point. 


Formula. 


Sp. Gr. 


Neutral Hydrocarbons. 








Liquid. 








Benzene, 


176° F. 


^6^6 


0-88 


Toluene, 


230° 


C 7 H 3 


0-87 


Xylene, 


284° 


Cs^io 


0-87 


Isocumene,* . 


338° 


C9H 12 


0-85 


Solid. 








Naphthalene, 


428° 


^10^8 




Anthracene, . 


680° . 


Qu^K) 




Chrysene, 




CisH 12 




Pyrene, .... 




Cl6H 10 




Alkaline Products. 








Ammonia, 




NH 3 




Aniline, 


360° 


C 6 H 7 N 


1*02 


Picoline, 


271° 


C 6 H 7 N 


0-96 


Quinoline, 


462° 


C 9 H 7 N 


1-08 


Pyridine, . . . 


240° 


C 5 H 5 N 




Acids. 








Carbolic acid, 


370° 


C 6 H 6 


1-07 


Kresylic ,, . . . •; 


397° 


C 7 H 8 




Rosolic ,, . . . 




Ci9H 14 3 




Brunolic ,, . 








Acetic ,, . 


243° 


C 2 H 4 2 


1-06 



The gas is now passed through the lime-purifier, which is an iron box 
with shelves, on which dryslaked lime is placed in order to absorb the 
carbonic acid gas and sulphuretted hydrogen, and the last portions of 
ammonia are removed by passing the gas through dilute sulphuric acid. 

A great many other methods have been devised for the purification of 
the gas from sulphuretted hydrogen, but none appears to be so efficacious 
and economical as that which consists in passing the gas over a mixture 
of ferrous sulphate (green vitriol or copperas), slaked lime, and sawdust 
(which is employed to prevent the other materials from caking together). 
The lime decomposes the ferrous sulphate, forming calcium sulphate and 
ferrous hydrate ; FeS0 4 + Ca(HO) ? = Fe('HO) 2 + CaS0 4 . 

The action of air upon the mixture soon converts the ferrous into 
ferric hydrate, which absorbs the sulphuretted hydrogen and the hydro- 
cyanic acid, producing with the former ferrous sulphide, and with the 
latter Prussian blue or some similar compound. The calcium sulphate 
existing in this purifying mixture is useful in absorbing any vapour of- 
ammonium carbonate from the gas, forming ammonium sulphate and 
calcium carbonate, f 

The action of the sulphuretted hydrogen on the ferric oxide may be 
thus represented, Fe 2 3 + 3H 2 S = 2FeS + S + 3H 2 ; and the circumstance 
which especially conduces to the economy of the process, is the facility 
with which the ferrous sulphide may be reconverted into the ferric oxide 
by mere exposure to the action of atmospheric oxygen, for 2FeS-f 3 
= Fe 2 3 + S 2 , thus reviving the power of the mixture to absorb sulphuret- 
ted hydrogen. Accordingly, if a small quantity of air be admitted into the 

* Benzene, originally derived from benzoic acid ; toluene, from balsam of tolu ; xylene, 
found among the products from wood (£v\ov) ; isocumene, isomeric with cumene, obtained 
from oil of cummin. 

f Ferric oxide, derived from various natural and artificial sources, is also employed for 
the purification of coal gas. 



PURIFICATION OF COAL GAS. 455 

purifier together with the gas, it reconverts the ferrous sulphide into ferric 
oxide, and the oxidation is attended with enough heat to convert into 
vapour any benzene which may have condensed in the purifying mixture, 
and of which the illuminating value would otherwise be lost. The same 
purifying mixture may thus be employed to purify a very large quantity 
of gas, until the separated sulphur has increased its bulk to an incon- 
venient extent, when it is distilled off in iron retorts. The various 
processes which have been devised for the removal of the carbon disulphide 
vapour are mentioned at page 218. 

The purified gas is passed into the gasometers, from which it is sup- 
plied for consumption. 

In the manufacture of coal gas, attention is requisite to the temperature 
at which the distillation is effected, for if it be too low, the solid and 
liquid hydrocarbons will be formed in too great abundance, not only 
diminishing the volume of the gas, but causing much inconvenience by 
obstructing the pipes. On the other hand, if the retort be too strongly 
heated, the vapours of volatile hydrocarbons, as well as the olefiant gas 
and marsh gas, may undergo decomposition, depositing their carbon 
upon the sides of the retort, in the form of gas-carbon, and leaving their 
hydrogen to increase the volume and dilute the illuminating power of the 
gas. 

These effects are well exemplified in the following analysis of the gas 
collected from Wigan cannel coal at different periods of the distillation : — 



In 100 volumes. 


1st hour. 


5th hour. 


10th hour. 

o-o 


Oiefiant gas and volatile hydrocarbons, 


13-0 


7-0 


Marsh gas, ..... 


82-5 


56-0 


20'0 


Carbonic oxide, 


3-2 


11-0 


io-o 


Hydrogen, 


o-o 


21-3 


60-0 


Nitrogen, ...... 


1-3 


47 


io-o 



The increase of the carbonic oxide after the first hour must be attri- 
buted to the decomposition of the aqueous vapour by the carbon as the 
temperature rises, and the increase of the nitrogen may probably be 
ascribed to the decomposition of the ammonia into its elements at a high 
temperature. 

323. One of the most useful of the secondary products of the coal gas 
manufacture is the ammonia, and this process has been already noticed as 
a principal source of the ammoniacal salts found in commerce. 

.Next in the order of usefulness stands the coal-tar, which deserves 
attentive consideration, not only on that account, but because the extrac- 
tion of the various useful substances from this complex mixture affords an 
excellent example of proximate organic analysis, that is, of the separation 
of an organic mixture into its immediate components. 

For the separation of the numerous volatile substances contained in 
coal-tar, advantage is taken of the difference in their boiling-points, which 
will be observed on examining the table at page 454. 

A large quantity of the tar is distilled in an iron retort, when water 
passes over, holding salts of ammonia in solution, and accompanied by a 
brown oily offensive liquid which collects upon the surface of the water. 
This is a mixture of the hydrocarbons which are lighter than water, viz., 
benzene, toluene, xylene, and isocumene, all having, as represented in the 



456 COAL-NAPHTHA. 

table at page 454, a specific gravity of about 085. 100 parts of the tar 
yield, at most, 10 parts of this light oil. 

As the distillation proceeds, and the temperature rises, a yellow oil 
distils over, which is heavier than water, and sinks in the receiver. This 
oil, commonly called dead oil, is much more abundant than the light oil, 
amounting to about one-fourth of the weight of the tar, and contains those 
constituents of. the tar. which have a high specific gravity and boiling- 
point, particularly naphthalene, aniline, quinoline, and carbolic acid. The 
proportion of naphthalene in this oil augments with the progress of the 
distillation, as would be expected from its high boiling-point, so that the 
last portions of the oil which distil over become nearly solid on cooling. 
When this is the case, the distillation is generally stopped, and a black 
viscous residue is found in the retort, which constitutes pitch, and is 
employed for the preparation of Brunswick black and of asphalt for 
paving. 

The light oil which first passed over is rectified by a second distillation, 
and is then sent into commerce under the name of coal-naphtha, a quan- 
tity of the heavy oil being left in the retort, the lighter oils having lower 
boiling-points. 

This coal-naphtha may be further purified by shaking it with sulphuric 
acid, which removes several of the impurities, whilst the pure naphtha 
collects on the surface when the mixture is allowed to stand. When this 
is again distilled it yields the rectified coal-naphtha. 

This light oil, especially when distilled from cannel coal at a low temperature, 
contains, in addition to the hydrocarbons above enumerated, some belonging to the 
marsh gas series (CmHo n+2 ), and others more recently brought to light, belonging to a 
series the general formula of which is OH 2m -2 ; but these last appear to be acted on 
by the sulphuric acid, employed to remove the basic substance's from the light oil, in 
such a manner that they are converted into polymeric hydrocarbons, having the 
general formula C>2nHin-i, of which tlie three following have been particularly 
examined : — 



Formula. 



^lfiH? 



Boiling-point. 
410° F. 
464° 
536° 



The hydrocarbons C 6 H 10 , C 7 H 12 , and C 8 H 14 , from which these appear to have been 
formed by the action of sulphuric acid, would evidently be the higher homologues 
of acetylene, C ? H 2 . 

The distillation of cannel coal, and of various minerals nearly allied to coal, at low 
temperatures, is now extensively carried on tor the manufacture of paraffin and 
paraffin oil (see Paraffin). 

The separation of the hydrocarbons composing this naphtha is effected 
by a process in constant use for similar purposes, and known as fractional 
distillation. 

This consists in distilling the liquid in a retort (A, fig. 282) through 
the tubulure of which a thermometer (T) passes, to indicate the tempera- 
ture at Which it boils. The first portion which distils over will, of course, 
consist chie fly of that liquid which has the lowest boiling-point; and if 
the receiver (R) be changed at stated intervals corresponding to a certain 
rise in the temperature, a series of liquids will be obtained, containing 
substances the boiling-points of which lie within the limits of temperature 
between which such liquids were collected. 

When these liquids are again distilled separately in the same way, a 
great part of each is generally found to distil over within a few degrees 



SEPARATION OF THE HYDROCARBONS. IN COAL-NAPHTHA. 457 

on either side of some particular temperature, which represents the boil- 
ing-point of the substance of which that liquid chiefly consists ; and if the 
receivers be again changed at stated intervals, a second series of distillates 
will be obtained, the boiling-points of which are comprised within a 
narrower range of temperature. It will be evident that, by repeated dis- 
tillations of this description, the mixture will eventually be resolved into 
a number of liquids, each distilling over entirely at or about one par- 
ticular degree, viz., the boiling-point of its chief constituent. 

To apply this to the separation of the constituents of light coal-naphtha. 
c The crude light oil is first agitated with dilute sulphuric acid, which removes any 
basic substances present in it, and afterwards 1 with a dilute solution of potash, to 
separate carbolic acid. The adhering potash is removed by shaking with water, and 
the naphtha is allowed to remain at rest, so that alJ the water may settle down, and 
the naphtha may be drawn off for distillation. 




Fig. 282. —Fractional distillation. 

The naphtha begins to boil at about 160° F., but only a small quantity distils over 
before the temperature has risen to 180°, when the receiver may be changed; between 
180° and 200° a considerable quantity of the naphtha distils oyer, and at the latter 
degree the receiver is changed a second time. The receiver is changed at every 20? 
throughout the distillation, until nearly the whole of the naphtha has passed over, 
which will be the case at about 360°. * 

Ten unequal quantities of liquid will have been thus obtained, diminishing as the 
temperature rises. 

Each of these must then be distilled in a smaller retort than the first, also provided 
with a thermometer. 

The first portion (160° to 180°) will probably begin to boil at 150°, and will distil 
in great part before 160°, when the receiver may be changed. When the temperature 
reaches 170° it will probably be found that nothing remains worth distilling. The 
liquid passing over in this distillation between 160° and 170° may be added to that 
which is next to be distilled (180° to 200°). 

The second portion (180° to 200°) will begin to boil at about 175°, and will distil 
over chiefly between that temperature and 185°, when the receiver may be changed. 
Nearly the whole will have passed over before 195°, and this last fraction may be 
added to that previously obtained from 200° to 220°. 

When all the first series of liquids have been thus distilled, it will be found that 
the second series consists chiefly of six portions distilling between the following 
degrees of temperature, viz., 150°-160°, 175°-185°, 180°-190°, 240°-250°, 300°-310°, 
340°-350°. 

* On the large scale, that portion of the naphtha which is distilled over between 180° 
and 250° F. is sold as benzene, and employed for the preparation of aniline. 



458 



BENZOLE OR BENZENE. 



By another distillation of each of these portions, a third series of liquids will be 
formed, consisting chiefly of five portions distilling between the following points, 
viz., 145°-150°, 175°-180°, 230°-235°, 288°-293°, 336°-342°. 

The portion distilling between 145° and 150° is comparatively small in quantity, 
and has not yet been fully examined. 

That obtained between 175° and 180° is more abundant than either of the others, 
and is nearly pure benzene (C 6 H 6 ). 

The portion boiling between 230° and 235° is chiefly toluene (C 7 H 8 ), whilst 288° to 
293° gives xylene (O 8 H 10 ), and 336° to 342° isocumene (C 9 H 12 ). 

In order to separate the benzene completely from the hydrocarbons which still 
adhere to it, the portion boiling between 175° and 180° is exposed to a temperature 
of 32° F., when the benzene alone freezes, the other hydrocarbons remaining liquid, 
and being easily extracted by pressure. 

A simple method of separating liquids which have different boiling-points consists 
in distilling them in a flask (F, fig. 283) connected with a spiral worm (W) of pewter 
or copper, surrounded by water, or some other liquid, maintained at a temperature 
just above the boiling-point of the particular liquid which is required to distil over. 
The greater part of the less volatile liquids will condense in the worm and run back 




Fig. 283.— Refluxing Condenser. 

into the flask. Thus, in extracting benzene from the light oil, the liquid in A might 
be kept at 180° F., when the toluene, &c, would be partly condensed in the worm, 
and the portion which passed into the receiver would consist chiefly of benzene. 
When little more distilled over, the temperature of A might be raised to 230°, and 
the receiver changed, when the distillate would contain toluene as its predominant 
constituent, and so on. 

324. Benzole or Benzene, C 6 H 6 .* — The pure benzene is a brilliant colour- 
less liquid, exhaling a powerful odour of coal gas; it boils at 176° F., and 
is very inflammable, burning with a smoky flame. It mixes readily with 
alcohol and wood-spirit, but not with water. Its property of dissolving 
caoutchouc and gutta-percha renders it very useful in the arts, and it is an 
excellent solvent for the removal of grease, paint, &c, from clothes and 
furniture. 

When benzene is treated with hydric peroxide, it is slowly converted into phenol 
(carbolic acid) C fi H 6 0. 

Benzene combines directly with chlorine to form a solid benzene chloride, C 6 H 6 C1 6 , 
which is decomposed by an alcoholic solution of potash, yielding chlorobenzene, 



* In commerce, the term benzole is usually applied to the lighter portions (of low 
boiling-point) distilled from coal-naphtha, whilst benzene is that distilled from petroleum. 



ANILINE OR PHENYL-AMINE. 459 

By the action of an aqueous solution of hypochlorous acid upon benzene, a crys- 
talline body has been obtained, having the composition C 6 H 9 C1 3 3 , and called tri- 
chlorhydrine of vhenose. When acted on by alkalies, this substance yields a sweet 
substance called phmose, isomeric with dry grape sugar — 

C 6 H 9 C1 3 3 + 3KHO = C 6 B. 12 6 {Pkenose) + 3KC1 . 

This substance has not been crystallised ; it forms a deliquescent amorphous mass, 
which is easily soluble in water and alcohol, but insoluble in ether. It reduces the 
oxides of copper and silver like grape-sugar, and when acted on by nitric acid is con- 
verted into oxalic acid. Phenose has not been found capable of fermentation by yeast. 

The benzene or aromatic series of hydrocarbons is generally 
represented as containing a double chain of six carbon atoms 
linked together by one and two bonds alternately, forming Q 

what is called the aromatic nucleus or Kekule's chain. It / SS. 

will be seen that each of the tetratomic carbon atoms has one ' vV 

free bond. If all these be attached to hydrogen atoms, & C C 2 

benzene C 6 H 6 is produced. By the successive replacement of 
these hydrogen atoms by CH 3 , the other aromatic hydro- 
carbons are formed. But the position of the particular rp p » 
Irydrogen atoms which are thus replaced influences the nature . 
of the product. Thus, if the group CH 3 be attached to each \^ ^/ 
of the carbon atoms marked 1 and 2 or 1 and 6, the resulting /\ * 
compound, C 8 H 10 , is orthorylene, boiling at 140° to 141° C. ; , 
whilst if CH 3 be attached to the carbon atoms marked 1 and ^ 
3 or 1 and 5, metaxylene, C 8 H 10 , boiling at 137° C, is obtained, and if the CH 3 be at- 
tached to the carbon atoms marked 1 and 4, paraxylenc or methyle-toluene, C 8 H 10 , 
is obtained. 

325. Aniline. — The chief purpose to which "benzene is devoted is the 
preparation of aniline, which is subsequently converted into the brilliant 
dyes now so extensively used. It has been already noticed at page 139, 
that when benzene is dissolved in fuming nitric acid, violent action takes 
place, and a dark red liquid is formed, from which water precipitates a 
heavy yellow oily liquid, smelling of bitter almonds, and known as nitro- 
benzoie or nitrobenzene, which has the composition C 6 ET 5 (X0 2 ), and may be 
regarded as derived from benzene by the substitution of a molecule of nitric 
peroxide for an atom of hydrogen ; C 6 H 6 + HjS"0 3 = C 6 H 5 (N0 2 ) + H 2 0. 

When nitrobenzene is placed in contact with diluted sulphuric acid and 
metallic zinc, the (nascent) hydrogen removes the whole of the oxygen, 
and 2 atoms of hydrogen are acquired instead, producing C 6 H 5 NH 2 , or 
C 6 H 7 X, aniline; C 6 H 5 (X0 2 )+ H 6 = C 6 H 7 X + 2H 2 0. 

That aniline has been produced may be shown by neutralising the 
excess of sulphuric acid with potash, and adding chloride of lime (hypo- 
chlorite of lime), which gives a fine purple colour writh aniline. 

The conversion of nitrobenzene into aniline on a large scale is more 
conveniently effected by gently heating it, in a retort, with iron borings 
and acetic acid, when the deoxidising action of the ferrous acetate 
Fe(C 2 H 3 2 ) 2 , first produced, materially assists the change, this salt being 
cou verted into a basic ferric acetate 2[Fe 2 (C 2 H 3 2 ) 6 ]Fe 2 3> which is left 
in the retort, and the aniline may be distilled over, accompanied by water. 
At the close of the distillation a red oil passes over, which solidifies to a 
crystalline mass. This is azobe?izide, C 6 H 5 X, originally obtained by dis- 
tilling nitrobenzene with an alcoholic solution of potash. 

(When nitrobenzene, in alcoholic solution, is reduced by zinc in the 
presence of hydrochloric acid, the solution neutralised by sodium car- 
bonate and boiled with alcohol, a crystalline compound of aniline with 
zinc chloride (ZnCl 2 .2C 6 H 7 N) is obtained.) 

Since aniline is only slightly soluble in water, and has the sp. gr. 1*02, 



460 DYES FEOM COAL-TAE. 

the larger portion of it collects at the bottom of the liquid in the receiver, 
which is milky from the presence of minute drops of aniline in suspension. 
By pouring the contents of the receiver into a tall vessel, the greater part 
of the aqueous fluid may be separated, and the aniline may be purified by 
a second distillation, when the remaining water will pass over first, the 
boiling-point of aniline being 360° F. 

Aniline * presents many striking features ; though colourless when per^ 
fectly pure, it soon becomes brown if exposed to the air : its odour is 
very peculiar, and somewhat ammoniacal, and its taste is very acrid. A 
drop falling upon a deal table stains it intensely yellow. But the charac- 
ter by which aniline is most easily recognised, and that which leads to 
its useful applications, is the production of a violet colour with solution 
of chloride of lime, by which a very minute quantity of aniline may be 
detected. The change of colour is due to oxidation, and a great number 
of processes have been patented from time to time for the production of 
crimson, purple, and violet dyes by the action of various oxidising agents 
upon aniline. 

326. Coal-tar dyes. — The first dye ever manufactured from aniline on a large scale 
was that known as mauve,\ or aniline purple, which is obtained by dissolving aniline 
in diluted sulphuric acid, and adding solution of bichromate of potash, when the 
liquid gradually becomes dark-coloured, and deposits a black precipitate, which is 
filtered off, washed, boiled with coal-naphtha to extract a brown substance, and after- 
wards treated with hot alcohol, which dissolves the mauve. The chemical change 
by which the aniline has been converted into this colon ring-matter cannot at 1 present 
be clearly traced, but the basis of the colour has been found to be a substance which 
has the composition C. 27 H. 24 ISr 4 , and has been termed mauveine. It forms black 
shining crystals, resembling specular iron ore, which dissolve in alcohol, forming a 
violet solution, and in acids, with production of the purple colour. Mauveine com" 
bines with the acids to form salts ; its alcoholic solution even absorbs carbonic acid 
gas. The hydrochlorate of mauveine, C 27 H 24 N 4 ,2HC1, forms prismatic needles with 
a green metallic lustre. 

Very brilliant red dyes are obtained from commercial aniline by the action of 
carbon tetrachloride, stannic chloride, ferric chloride, cupric chloride, mercuric 
nitrate, corrosive sublimate, and arsenic acid. It will be noticed that all these agents 
are capable of undergoing reduction to a lower state of oxidation or chlorination, 
indicating that the chemical chancre concerned in the transformation of aniline into 
aniline-red is one in which the aniline is acted on by oxygen or chlorine. 

The easiest method of illustrating the production of aniline-red, on the small scale, 
consists in heating a few drops of aniline in a test-tube with a frogmen t of corrosive 
sublimate (mercuric chloride), which soon fuses and acts upon the aniline to 
form an intensely red mass composed of aniline-red, calomel, and various secondary 
products. By heating this mixture with alcohol the red dye is dissolved, and a skein 
of silk or wool dipped into the liquid becomes dyed of a fice red, which is not removed- 
by washing. 

On the large scale, magenta (as aniline-red is commonly termed) is generally pre- 
pared by heating aniline to about 320° F. with arsenic acid, when a dark semi-solid 
mass is obtained, which becomes hard and brittle on cooling, and exhibits a green 
metallic reflection. This mass contains, in addition to aniline-red, several secondary 
products of the action, and arsenious acid. On boiling it with water, a splendid 
red solution is obtained, and a dark resinous or pitchy mass is left. If common salt 
be added to the red solution as long as it is dissolved, the bulk of the colouring 
matter is precipitated as a resinous mass, which may be purified from certain 
adhering matters by drying and boiling with coal-naphtha. The red colouring 
matter is the arseniate of a colourless organic base, which has beeu called rosanilinc, 
and has the composition C 20 H ]9 N" S . H 2 0. If the red solution of arseniate of rosaniline 
be decomposed with calcium hydrate suspended in water, a pinkish precipitate is 

* Aniline derives its name from anil, the Portuguese for indigo, from which it may be 
obtained by distillation with potash. 
( f French for marsh-mallow, in allusion to the colour of the flower. 



CHRYS ANILINE — ANILINE-BLUE. 461 

obtained, which consists of rosaniline mixed with calcium arseniate, and the solution 
entirely loses its red colour. 

By treating the precipitate with a small quantity of acetic acid, the rosaniline is 
converted into rosaniline acetate (C 2n H 19 N 3 ,C 2 H 4 2 ), forming a red solution, which, 
may be filtered off from the undissolved calcium arseniate. On evaporating the 
solution to a small bulk, and allowing it to stand, the acetate is obtained in crystals 
which exhibit the peculiar green metallic lustre of the wing of the rose-beetle, 
characteristic of the salts of rosaniline. This salt is the commonest commercial form 
of magenta ; its colouring power is extraordinary, a very minute particle imparting 
a red tint to a large volume of water. Silk and wool easily extract the whole of the 
colouring matter from the aqueous solution, becoming dyed a fast and brilliant crim- 
son ; cotton and linen, however, have not so strong an attraction for it, so that if a 
pattern be worked in silk upon a piece of cambric, which is then immersed in a 
solution of magenta and afterwards washed in hot water, the colour will be washed 
out of the cambric, but the red silk pattern will be left. 

If a boiling solution of rosaniline acetate be mixed with excess of ammonia, the 
bulk of the rosaniline will be precipitated, but if the solution be filtered while hot, 
it deposits colourless needles of rosaniline, which become red when exposed to the 
air, from absorption of carbonic acid, and formation of the red rosaniline carbonate. 

Water dissolves but little rosaniline; alcohol dissolves it abundantly, forming a 
deep red solution. Rosaniline forms two classes of salts Avith acids, those with 
1 molecule of acid {monacid salts) being crimson, and those with 3 molecules 
(triacid salts) having a brown colour. Thus, if colourless rosaniline be dissolved in 
a little dilute hydrochloric acid, a red solution is obtained, which contains the 
monacid rosaniline hydrochlorate, C 20 H ]9 N 3 .HC1 ; but if an excess of hydrochloric 
acid be ad'led, the red colour disappears, and a brown solution is obtained, from which 
the triacid hydrochlorate, Co H 19 lSr 3 .3HCl, may be crystallised in brown-red needles. 

For experimental illustration of the properties of rosaniline, the liquid obtained by 
boiling a solution of the acetate with a slight excess of lime diffused in water, and 
filtering while hot, is very well adapted. The solution has a yellow colour, and may 
be preserved in a stoppered bottle without alteration. If air be breathed into it 
through a tube, the liquid becomes red from production of rosaniline carbonate. 
Characters painted on paper with a brubh dipped in the solution are invisible at first, 
but gradually acquire a beautiful rose colour. 

When the red solution of rosaniline hydrochlorate is slightly acidified with hydro- 
chloric acid and placed in contact with zinc, the solution becomes colourless, the 
rosaniline acquiring 2 atoms of hydrogen, and becoming leucaniline (from XevKbs, 
white) C 20 H 21 jST 3 , the hydrochlorate of which (C 2? H 21 N 3 .3HC1) forms a colourless 
solution. Oxidising agents reconvert the leucaniline into rosaniline. It has been 
observed that pure aniline does not yield aniline-red when heated with corrosive 
sublimate or arsenic acid, it being necessary that it should contain another organic 
base, toluidine (C 7 H 9 lSn, which is derived from toluene (C 7 H 8 ) in the same way in which 
aniline is derived from benzene. Since the benzene obtained from coal-naphtha almost 
invariably contains toluene, the aniline obtained from it is very seldom free from 
toluidine. If the aniline be prepared with benzene derived from -benzoic acid, and 
therefore free from toluene, no red is obtained. A mixture of 70 parts of toluidine 
with 30 of aniline is said to answer best for the preparation of the red and violet 
colouring matters. Such a mixture would contain 2 molecules of toluidine (C 7 H 9 ;N") 
and 1 of aniline (C 6 H 7 N), or C 20 H 25 ri 3 , only requiring the removal of H 6 by an oxidis- 
ing agent to yield rosaniline C 20 H 19 N" :! . 

Aniline-yelloiv or chrysaniline (from xpveeos, golden) is found among the secondary 
products obtained in the preparation of aniline-red. It forms a bright yellow 
powder, resembling chrome-yellow, and having the composition C 20 H 17 N 3 . It is 
nearly insoluble in water, but dissolves in alcohol. Chrysaniline has basic properties 
and dissolves in acids, forming salts. On dissolving it in diluted hydrochloric acid, 
and mixing the solution with the concentrated acid, a scarlet crystalline precipitate 
of chrysaniline hydrochlorate (C 20 H 17 N 3 .2HC1) is obtained, which is insoluble in 
strong hydrochloric acid, but very soluble in water. A characteristic feature of 
chrysaniline is the sparing solubility of its nitrate. Even from a dilute solution of 
the hydrochlorate, nitric acid precipitates chrysaniline nitrate (C 20 H 17 X 3 .HNO 3 ) in 
ruby-red needles. 

Aniline-blue is produced when a salt of rosaniline (the commercial acetate, for 
example) is boiled with an excess of aniline, which converts the rosaniline (C 20 H l9 ISr 3 ) 
into triphenylic rosaniline (C 20 H 16 (C,.H 5 ) 3 ]Sr 3 ), which may be regarded as having been 
formed by the introduction of 3 atoms of the hypothetical radical phenyle (C 6 H 5 ) 



46 2 HYDROCYAN-ROS ANILINE — PHEN YLAMINE. 

in place of 3 atoms of hydrogen, the latter having been evolved in the form of 
ammonia — 

C 20 H 19 N- 3 HC1 + 3[(C 6 H 5 )H,N] = C 20 H 1fi (C fi H 5 ) 3 N 3 .HCl + 3NH 3 . 

Rosaniline . .,. . Triphenylic rosaniline 

hydrochlovate. • rae " hydrochlorate. 

The hydrochlorate is an ordinary commercial form of aniline-blue ; it has a brown 
colour, refuses to dissolve in water, but yields a fine blue solution in alcohol. If it 
be dissolved in an alcoholic solution of ammonia, the addition of water causes a white 
precipitate of the hydrated base, triphenylic rosaniline, C 20 H 16 (C 6 H 5 ) 3 ]Sr 3 .H 2 O, which 
becomes bluish when washed and dried. 

Just as rosaniline yields leucaniline when acted on with nascent hydrogen, so tri- 
phenylic rosaniline yields triphenylic leucaniline (C 20 H 18 (C 6 H 5 ) 3 N 3 ; this is not basic 
like leucaniline, but a neutral colourless substance, which is reconverted into blue by 
oxidising agents. Compounds corresponding to triphenylic rosaniline, but containing 
methyle, ethyle, or amyle in place of phenyle, are obtained by digesting rosaniline 
with the iodides of these radicals, at a high temperature, in sealed tubes. Thus, by 
the action of ethyle iodide (C 2 H 5 I) upon rosaniline, a blue crystalline body insoluble 
in water, but soluble in alcohol, is obtained, which is a compound of ethyle iodide 
with triethylic rosaniline ; C 20 H 16 (C 2 H 5 ) 3 !N" 3 . 

C 30 H 19 Sr 3 + 4C 2 H 5 I = C 20 H ]6 (C 2 H 5 ) 3 N 3 .C 2 H 5 I + 3HI . 

Rosaniline. ^ffiS 116 

ethyl-iodate. 

Aniline-violet is formed in a similar manner with methyle iodide. Other com- 
pounds have been obtained from aniline, presenting almost every variety of colour. 
A green dye is prepared by the action of a mixture of hydrochloric acid and potassium 
chlorate upon aniline, and under particular conditions a black may be obtained with 
the same agents. Another green has been made by acting upon magenta with 
aldehyde. 

When a solution of rosaniline acetate is treated with potassium cyanide, it gradually 
loses its red colour, and deposits a white crystalline precipitate of a base which has 
been termed hydrocyan-rosaniline, having the formula C 21 H 20 N 4 , and containing the 
elements of rosaniline and hydrocyanic acid ; but this acid cannot be detected in it 
by the ordinary tests, leading to the belief that the new base should be regarded as 
leucaniline (C 20 H 21 N 3 ), in which one atom of hydrogen is replaced by cyanogen 
(C 20 H 20 (CN)]Sr 3 ). The hydrocyan-rosaniline is almost insoluble in water, and 
sparingly soluble in boiling alcohol. When precipitated from its salts by adding an 
alkali, it becomes pink on exposure to sunshine. 

The present extensive application of aniline to the manufacture of these 
dyes affords a most striking example of the direct utility of pure chemistry 
to the arts ; for, twenty-five years ago, the name of this substance was 
not known to any but scientific chemists, whilst at present many tons are 
annually consumed to supply the wants of the dyers of silk and woollen 
goods. 

327. Aniline ranks as a powerful organic base, combining readily with 
acids to form salts which are, generally speaking, easily crystallised. Like 
ammonia, it unites directly with the acids, without any separation of 
water; thus, the formula of aniline sulphate is 2C 6 H 7 KH 2 S0 4 , hydro- 
chlorate of aniline is C 6 H 7 KHC1, and exactly as the addition of potash 
to the salts of ammonia causes the separation of ammoniacal gas, so when 
added to the salts of aniline, it precipitates that base in the form of oily 
drops, which render the liquid milky. This resemblance in disposition 
between aniline and ammonia leads to the impression that they must be 
moulded after a common type, and, accordingly, aniline is often represented 
as formed from ammonia (ISTH 3 ) by the substitution of the compound 
radical phenyle (C r H 5 ) for an atom of hydrogen, and upon this supposition 
is termed phcnylamine, NH 2 (C ( .H 5 ) = C 6 H 7 N. 

This view of the constitution of aniline is supported by the circum- 
stance of its formation when phenic or carbolic acid is heated with 



HOMOLOGUES OF BENZENE. 4b6 

ammonia in a tube hermetically sealed; for there is reason to believe that 
this acid, mentioned above as one of the chief acid products of the 
destructive distillation of coal, is phenylic hydrate (C 6 H 5 )HO, and its 
action upon ammonia would then be clearly explained by the equation — 

(C 6 H 5 )HO + NH 3 = H 2 + NH 2 (C 6 H 5 ) 

Phenic acid. Aniline or phenylamine. 

When aniline is dissolved in alcohol and acted on by nitrous anhydride, 2 mole- 
cules of it lose 3 atoms of (monatomic) hydrogen, and acquire, in their stead, 1 atom 
of (triatomic) nitrogen, depositing a yellow compound, which has been called dia- 
zoamidobenzene — 

4C 6 H 7 N + N 2 3 = 2C 12 H n N 3 + 3H 2 0. 
Aniline. Diazoamidobenzene. 

When N 2 3 acts upon a hot solution, a base is formed isomeric with the above, and 
called amido-diphenylimidc, which is identical with a yellow colouring matter obtained 
by the action of sodium stannate upon a salt of aniline. Its slightly acid solutions 
impart an intensely yellow colour to silk or wool, which is removed by heat, the 
base being volatile. The action of nitrous anhydride on aniline affords an example 
of a general method of producing compounds in which nitrogen is substituted for 
hydrogen. 

By acting upon one of the salts of aniline with N 2 3 , a salt of diazobenzene C 6 H 4 N 2 
is obtained. This may be represented as being derived from aniline C 6 H 7 N, by the 
substitution of one atom of triatomic nitrogen for three atoms of hydrogen. The 
salts of diazobenzene are very explosive. 

Diazobenzene nitrate C 6 H 4 N 2 .HN0 3 is prepared by passing N 2 3 gas into a strong 
aqueous solution of aniline nitrate until a little of the solution no longer gives a 
turbidity with potash. Alcohol then precipitates the diazobenzene nitrate in colour- 
less prisms ; 2(C 6 H 7 N.HN0 3 ) + N 2 3 ==2(C 6 H 4 N 2 .HN0 3 ) + 3H 2 0. This salt is said 
to be as sensitive to a shock as mercuric fulminate, and has been proposed for use in 
detonating primers. When heated it detonates with extreme violence at 90° C, 
whilst mercuric fulminate requires 195° C. 

Accompanying the aniline in coal-tar, there are found three other bases, 
viz., pyridine, picoline, and quinoline. It will be seen that picoline 
(C 6 H 7 N) is isomeric with aniline, from which, however, it differs in a 
very striking manner, for its salts are by no means easily crystallisable, 
and it furnishes no violet colour with oxidising agents, such as chloride 
of lime. Picoline occurs among the products of the distillation of bones. 
Quinoline is also formed when some of the vegetable alkaloids are distilled 
with potash. 

Quinoline has been obtained by the action of strong sulphuric acid upon 
a mixture of nitrobenzene, aniline, and glycerine; C 6 H 5 N0 9 + 2C 6 HhX 
+ 3C 3 H 8 3 = 1 1 H 2 + 3C n H v N {Quinoline). 

328. The other constituents of the light coal-naphtha, viz., toluene, 
xylene, and isocumene, belong to the benzene series of hydrocarbons 
(page 438). 

On reference to the table at page 454, it will be seen that the boiling- 
points of the members of this series are raised 54° F. for each addition of 
CH 2 . Thus xylene (C 8 H 10 ) boils at 284°, or 54° higher than toluene 
(C 7 H 8 ), which boils at 230° ; whilst benzene (C 6 H 6 ) boils at 54° below 
this, or 176°. 

The members of this group are also intimately connected with those 
of another homologous series, known as aromatic acids, including — 

Benzoic acid, . . C 7 H 6 2 
Toluic acid, . . C 8 H 8 2 
Cuminic acid, . . C 10 H 12 O 2 . 

By distilling each of these acids with barium hydrate, the correspond- 



464 PHENOLE OE CARBOLIC ACID. 

ing hydrocarbon is obtained, a molecule of C0 2 being removed by the 
barium hydrate ; thus, C 7 H 6 2 {Benzoic acid)-- C0 2 = C 6 H 6 (Benzene). 

The similarity between this decomposition and that by which marsh 
gas (CH 4 ) is derived from acetic acid (C 2 H 4 2 ) will be at once apparent 
(see page 98). 

Each member of the benzene series of hydrocarbons, when acted upon 
by nitric acid, yields a nitro-compound corresponding in composition to 
nitrobenzene, and this, under the influence of reducing agents (such as 
ferrous acetate, or an alkaline hydrosulphate, or stannous chloride) yields 
a base homologous with aniline. 

Thus we have the three following homologous series : — 



Hydrocarbon. 


Nitro-compound. 


Base. 




Benzene, C 6 H 6 


Nitrobenzene, C P H 5 N0 2 


Aniline, 


C 6 H 7 N 


Toluene, C 7 H 8 


Nitrotoluene, C 7 H 7 N0 2 


Toluidine, 


C,H 9 ff 


Xylene, C 8 H 10 


Nitroxylene, C 8 H 9 N0 2 


Xylidine, 


C 8 H 1] N. 



When benzene is dissolved in concentrated sulphuric acid, the solution diluted, and 
neutralised with chalk, the liquid filtered from the calcium sulphate contains the 
calcium salt of sutyhobenzolic or benzene-sulphonic acid (acid phenyle sulphite) — 

C 6 H 6 + H 2 S0 4 = H 2 + C 6 H 5 S0 3 H {Sulphobenzolic acid). 

The acid itself may be obtained in crystals. 

Toluene -sulphonic acid, C 7 H 8 S0 3 , is formed in a similar way. By fusing the potash 
salts of these acids with caustic potash, the corresponding phcnoles are obtained; thus — 

C 6 H 5 S0 3 K + KHO = K 2 vS0 3 + C 6 H 5 OH 

Potassium benzene Potassium p . n , 

sulphonate. sulphite. -fnenoie. 

Each hydrocarbon of this series furnishes a sulpho-acid and a phenole ; thus — 
Hydrocarbon. Sulpho-acid. Phenole. 



Benzene, 
Toluene, 
Xylene, 



Benzene-sulphonic, C 6 H 6 S0 3 
Toluene-sulphonic, C 7 H 8 S0 3 
Xylene-sulphonic, C 8 H 10 SO 3 



C 7 H 8 



329. Carbolic or phenic acid, or pJienole (C 6 H 6 0), derives its interest 
chiefly from its constituting a great part of the ordinary commercial 
kreasote (from Kpea?, flesh, and o-oj£gj, to preserve). It is also present in 
cow's urine and in that of some other animals. It is found chiefly in 
the heavy or dead oil of coal-tar (page 456), particularly in that portion 
which distils over between 300° and 400° F., when the oil is submitted 
to fractional distillation, and it appears to be the carbolic acid which 
confers upOn this heavy oil its valuable antiseptic properties, leading to 
its employment for the preservation of wood from decay. 

In order to extract the acid from that portion of the dead oil which distils between^ 
300° and 400° it is treated with caustic soda. A crystalline mass is deposited which 
is separated from the liquid portion and heated with a little water, when a solution 
of sodium carbolate is obtained. This is separated from a quantity of oil which floats 
above it, and decomposed with sulphuric acid, when the carbolic acid separates as 
an oily layer upon the surface. This is drawn off, digested with a little fused calcium 
chloride to remove the water, and, distilled. The distilled liquid, when exposed to 
a low temperature, solidifies to a mass of long colourless needles, which are easily 
liquefied by heat. 

Carbolic acid has the peculiar taste and smell of kreasote. It dissolves 
sparingly in water, but readily in alcohol. When a piece of deal is wetted 
with solution of carbolic acid, and afterwards with hydrochloric acid, it 
becomes blue on drying. 

The genuineness of a commercial sample of carbolic acid may be tested by shaking 
about a drachm of it with half a pint of warm water, which will dissolve the pure 



PICRIC OR CARBAZOTIC ACID. 465 

acid entirely, but will leave any "dead oil" undissolved. A solution of 1 part of 
caustic soda in 10 parts of water should dissolve 5 parts of pure carbolic acid. 

When carbolic acid is shaken with one-fourth of its weight of water, and exposed 
to a temperature of 39° F., it deposits six-sided prismatic crystals of a hydrate, 
2C 6 H 6 O.H 2 0, which is soluble in water, alcohol, and ether, and fuses at 61° F. 

The acid properties of carbolic acid arc of a very feeble and doubtful character. 
It is the representative of the class of phenolcs which resemble the alcohols in com- 
position, but are distinguished from them by their tendency to combine with alkalies. 
Carbolic acid, or phenole, or phenyle hydrate, C 6 H 5 (OH). 

When distilled with chloride of zinc or of aluminium, phenole yields phenyle ether or 
diphenyle oxide (C 6 H 5 ). 2 0, and a compound 0(C 6 H 4 ) 2 CH 2 . When this is acted on by 
oxidising agents, it yields a ketone containing 0(C R H 4 ). 2 CO. On fusing this with 
potash it yields potassium salicylate HO(C 6 H 4 )CO,K, and potassium phenate 
C 6 H 5 OK. 

The aqueous solution of phenole gives a purple blue colour with ferric chloride, and 
a pale yellow precipitate with bromine water (trior -omophenole C 6 H 3 Br 3 0) ; this is an 
exceedingly delicate test for phenole. 

By the action of zinc chloride on mixtures of alcohols with phenole, the elements of 
water are abstracted, and phenoles are obtained in which alcohol radicals replace 
hydrogen; thus phenole and amylic alcohol yield amylephenole, C 6 H 4 5 H n .OH. 

Carbolic acid is very largely used as an antiseptic agent. In medicine 
it is found very valuable, especially for the treatment of putrid sores ; 
and, in admixture with sulphite of lime, it forms the substance known as 
MacDougalVs disinfectant. Calvert's disinfecting powder consists of clay 
with 12 or 15 per cent, of carbolic acid. 

330. Picric acid. — When carbolic acid is boiled with fuming nitric 
acid, the solution, on cooling, deposits beautiful yellow crystals of carba- 
zotic or picric acid, also called trinitrophenic or nitrophenisic acid, because 
it appears to be formed from phenic acid by the substitution of 3ISI"0 2 for 
H 3 , just as nitrobenzene is formed from benzene by the substitution of 
3T'0 2 for H. 

The composition of picric acid, upon this view, would be expressed by 
the formula HC 6 H 2 (N0 2 ) 3 0, the atom of hydrogen being capable of dis- 
placement by a metal, forming a picrate or carbazotate ; thus if the acid 
be added to a solution of potash, a yellow precipitate of potassium 
carbazotate or picrate, KC 6 H 2 (Js0 2 ) 3 0, is obtained, which has led to the 
employment of this acid as a test for potassium. 

Picric acid is not easily soluble in water, but dissolves readily in alcohol. 
Its solutions have the property of staining the skin and other organic 
matters yellow, which is turned to advantage by the silk-dyer. The 
intensely bitter taste of the acid has also led to its employment for the 
adulteration of beer, to simulate the bitter of the hop. 

Picric acid is a very common product of the action of nitric acid upon 
organic substances ; indigo, silk, and many resins furnish it in consider- 
able quantity. It is economically obtained in a pure state by the action 
of nitric acid upon Botany Bay gum, but considerable quantities are 
manufactured for the dyer by treating the crude carbolic acid from coal- 
tar with nitric acid. Picric acid, as might be anticipated from its com- 
position, explodes when sharply heated, its carbon and hydrogen being 
oxidised by the nitric peroxide. 

The picrates of potassium and ammonium are far more explosive than 
the acid itself, particularly when mixed with nitre. Such mixtures have 
been employed instead of gunpowder for blasting, and as bursting charges 
for shells. 

2g 



466 PICRIC OR CARBAZOTIC ACID. 

If 1 part of picric acid be dissolved in 9 parts of hot water, and the solution added 
gradually to 2 parts of potassium cyanide dissolved in 4 of water at 60° C, the solu- 
tion becomes deep red, and deposits brown crystalline scales with a green lustre. 
These consist of potassium isopiirpitrate or picrocyamatc, KC 8 H 4 N 5 6 , a salt which 
explodes violently when heated. When decomposed with ammonium chloride, it 
gives the ammonium isopurpurate which resembles murexide, and is used in dyeing. 

When picric acid is distilled with chloride of lime, it yields a heavy 
colourless oil having a very pungent odour of mustard, and boiling at 
235° F. This substance has been called chloropicrine or nitrocldoroform, 
and has the remarkable formula CC1 3 (X0 2 ), which may be represented as 
formed upon the type of marsh gas, CH 4 , in which 3 atoms of the 
hydrogen are replaced by chlorine, and the fourth by nitric peroxide. 
Mills has obtained it by the action of red nitric acid upon chloroform 
(CHC1 3 ). Chloropicrine is frequently met with among the products of 
the action of chlorinating agents upon organic substances. It is almost 
insoluble in water, but dissolves easily in alcohol and ether. 

When an alcoholic solution of chloropicrine is acted on by sodium, it 
yields the ethyle subcarbonate, and when treated with potassium cyanide, 
it exchanges 2 atoms of chlorine for cyanogen, forming an unstable dark 
red semi-fluid substance, having the composition CClCy 2 (]N"0 2 ), which 
may be regarded as derived from marsh gas (CH 4 ) by the substitution of 
2 atoms of cyanogen, 1 atom of chlorine, and 1 atom of nitric peroxide, 
for the 4 atoms of hydrogen. 

By the action of nascent hydrogen (distillation with acetic acid and 
iron filings), chloropicrine is converted into methylamine — 

CC1 3 ]S T 2 + H 12 = NH 2 .CH 3 + 2H 2 + 3HC1. 

Chloropicrine. Methylamine. 

It will be instructive to compare the composition of the most impor- 
tant members of the phenyle series, as that group of organic compounds is 
termed, which contain the radical phenyle (C 6 H 5 ). 

Benzole or phenyle hydride, . . . (C 6 H 5 )H 

Aniline or phenylamine, .... (C 6 H 5 )]SrH 2 

Phenic acid or phenyle hydrate, . . . (U 6 H 5 )OH 

Trinitrophenic or picric acid, . . . [C 6 H 2 (NOo) 3 ]OH. 

It is evident that whilst aniline may be regarded as ammonia in which 
phenyle is substituted for an atom of hydrogen, phenic acid can be 
represented as formed from a molecule of water by the substitution of 
phenyle for half the hydrogen, and benzene may be represented as a 
molecule of hydrogen, HH, in which one of the atoms is replaced by 
phenyle. 

Some specimens of the kreasote found in commerce boil at a higher 
temperature than carbolic acid ; this is due to the presence of kresylic 
acid or kresole (C r H 8 0), corresponding to carbolic acid, but regarded as 
containing the radical krcsyle (C 7 H 7 ) in place of phenyle. The analogy 
in composition is attended with a resemblance in properties, for kresylic 
acid has the same antiseptic property as carbolic acid, and is applicable 
to similar purposes. "When acted on by nitric acid, it yields trinitro- 
Tcresylic acid (HC 7 H 4 (N'0 2 ) 3 0), just as carbolic acid gives trinitrophenic 
acid (HC 6 H 2 (N0 2 ) s O). 

Aurine, C 19 H 14 3 , is a yellow crystalline body obtained in the prepara- 
tion of corallin by the action of a mixture of sulphuric and oxalic acids 
upon phenole — 



NAPHTHALINE OR NAPHTHALENE. 467 

3C 6 H 6 (OH) + H 2 C 2 4 = 3H 2 + CO + C 19 H 14 3 . 
It is dissolved by alkalies and reprecipitated by hydrochloric acid. 

331. Naphthaline or naphthalene.— The most prominent constituent 
of the heavy oil of coal-tar is the naphthalene, which is easily procured in 
a pure state from the portions obtained at the close of the distillation, by 
simply pressing the semi-solid mass to remove any liquid hydrocarbon?, 
and boiling with alcohol, from which the naphthalene crystallises on 
cooling in brilliant pearly flakes, which may be still further purified by 
the process of sublimation. 

In itself naphthalene is not very interesting, being a remarkably in- 
different substance,"" but it has been made the subject of several beauti- 
ful investigations which have thrown much light upon the action of 
chemical agents on organic compounds in general. 

The most important of these researches is that upon the action of 
chlorine and bromine on naphthalene, which originated the now almost 
universally accepted doctrine of substitution, and fully established the fact, 
that an element may be replaced in a given compound by an equivalent 
quantity of another element of a totally different chemical character. 

Thus, by the action of chlorine upon naphthalene, the hydrogen is 
removed in the form of hydrochloric acid, and there are obtained six new 
compounds by the progressive substitution of chlorine for the hydrogen, 
which Laurent distinguished by names indicating the number of atoms 
of chlorine present by means of the different vowels in the last syllable, 
introducing a new penultimate syllable when the vowels were exhausted, 
as will be seen in the following list : — 

Naphthalene, . 

Chlonaphtase, . 

Chlonaphtese, , 

Chlonaphtise, . 

Chlonaphtose, . 

It will be observed that the original naphthalene type is here preserved 

throughout, the sum of the atoms being always 18, and the number of 

carbon atoms 10. 

One of the most unexpected results of Laurent's investigation was the 

discovery that some of these compounds may be obtained in several 

distinct forms or modifications, which are isomeric, or have the same 

composition, but exhibit very different properties. Thus there are seven 

varieties of chlonaphtese, all containing C 10 H 6 C1 2 , and yet differing from 

each other as much as substances not having the same composition. 

Two of them are liquids, and the five solid forms all fuse at different 

temperatures, ranging between 88° and 214° F. Seven different forms of 

chlonaphtise likewise exist, and four of chlonaphtose. 

To account for this, Laurent supposed it to be by no means indifferent 

which atom of hydrogen has been removed from the compound, believing 

each to have its assigned place and specific function. Thus it may easily 

be conceived that the replacement of different atoms of hydrogen by 

chlorine should give the seven modifications of chlonaphtese — 

Naphthaline, C 10 H HHHHHHH 

Chlonaphtese a, C 10 C1 C1HHHHHH 

Chlonaphtese (3, C 10 H HC1C1HHHH, 

* A crimson dye, magdala, containing the base azo-dinaphthylamine, C 30 H 21 N3, has been 
prepared from naphthalene. 



Cn)H 8 


Chlonaphtuse, . 


Wanting 


C 10 H 7 C1 


Chlonaphthalase, 


C 10 H 2 C1 B 


C 10 H 6 C1 2 


Chlonaphthalese, 


Wanting 


CioH5^'3 


Chlonaphthalise, 


C 10 C1 8 


C 10 H 4 C1 4 







468 SUBSTITUTION PRODUCTS FROM NAPHTHALENE. 

and so on. Other more recent investigations have given greater prob- 
ability to this hypothesis. 

Bromine, as might be anticipated, yields results similar to those with 
chlorine; but it could not have been predicted that substitution com- 
pounds might be obtained in which one part of the hydrogen is replaced 
by chlorine and the other by bromine. Thus, by acting upon a chlorine 
substitution compound with bromine, or vice versd, the following sub- 
stances were produced :* — 

Chlorebron aphtise, 
Chlorebronaphtose, 
Chlorib ronaphtose, 
Bromechlonaphtuse, 
Bromachlonaphtose, (J 10 H 4 BrCJ 3 

It will be observed that chloribronaphtose and bromachlonaphtose 
have the same composition, though they possess different properties, and 
are obtained in very different ways, the former being procured by the 
action of bromine on chlonaphtise (C 10 H 5 C1 3 ), and the latter by the 
action of chlorine upon bronaphtese (C 10 H 6 Br 2 ). Another confirmation 
is thus obtained of the belief, that upon the position of the hydrogen 
which is replaced, depends the character of the resulting compound. 

According to modern chemical views, the carbon- 

J J atoms in naphthalene are regarded as being linked 

/- Q together to form two "rings." The tetratomic atoms 

// \ / ^S. being linked together by single and double bonds 

'/ ^ ■' r ? alternately, there are eight free bonds for the attach- 

2 C C ment of atoms of hydrogen or of any radical replacing 

1 1 hydrogen. The isomeric substitution derivatives are 

f } I ■ ' ~ then distinguished by indicating the numbers of the 

3 C C v> & carbon-atoms to which the radical is attached. Thus 

>\ / \ // the different varieties of chlonaphtese, C 10 H 6 C1 2 , are 

Vr ' C distinguished as 1 : 1' dichloronaphthalene, 1 : 2,1:3 

• ji i and 1 : 3', according to the position of the carbon- 

atoms to which the chlorine-atoms are attached. 

Naphthalene is capable of direct union with chlorine to form two 
naphthalene chlorides, having the formulae C 10 H 8 C1 2 and C 10 H 8 C1 4 , which 
may obviously be regarded as composed of substitution products combined 
with hydrochloric acid. 

When acted upon by nitric acid, naphthalene furnishes three substitu- 
tion products, in which 1, 2, and 3 atoms of hydrogen are replaced 
by JS"0 2 ; and each of these compounds, under the influence of reducing 
agents, yields a base, just as nitrobenzene, under similar treatment, yields 
aniline. 

By prolonging the action of boiling nitric acid upon naphthalene, 
and evaporating the solution, crystals of naphthalic or phthalic acid, 
H 2 C 8 H 4 4 , are obtained. Through this acid, naphthalene is connected 
with the phenyle series; for when phthalic acid is heated with lime, it 
yields calcium carbonate and benzene; H 2 C 8 H 4 4 + 2CaO = C 6 H 6 + 2CaC0 3 . 

Moreover, by digesting calcium phthalate with calcium hydrate at an 
elevated temperature for several hours, it is converted into benzoate and 
carbonate of calcium; .2CaC 8 H 4 4 + Ca(HO) 2 = Ca(C 7 H 5 2 ) 2 + 2CaC0 3 . 

Calcium phthalate. Calcium benzoate. 

* In naming these compounds, Laurent proceeded upon the same principle. The vowel 
immediately after the syllable chlor- or brom-, indicating the number of atoms of that 
element, whilst the vowel in the last syllable shows how many atoms of hydrogen have 
been replaced. The name begins with chlor- when the compound has been obtained by 
the action of bromine upon a chlorine substitution product, and vice versd. 



ANTHRACENE. 469 

By the action of heat upon phthalic acid, the anhydride, C 8 H 4 3 , is 
obtained in needle-like crystals. This, when heated with resorcine to 
200° C, yields fluoresceins, C 20 H 12 O 5 , as a brown crystalline body dis- 
solved by ammonia to a red solution having a green fluorescence. Acetic 
acid also dissolves it, and on adding bromine to the solution, a feebly 
acid body crystallises out which is called cosine, C 20 H 8 Br 4 O 5 ; the potas- 
sium salt, C 20 H 6 K 2 Br 4 O 5 , is known in commerce as soluble eosine, and 
forms a fine red dye. Fluoresceine is employed as a yellow dye on silk. 

Resorcine, C 6 H 4 (OH) 2 , is a very soluble crystalline phenole obtained 
by distilling the extract of Brazil-wood, or by the action of sodium 
hydrate upon benzene-disulphonic acid obtained by the action of sulphuric 
acid on benzene. 

Anthracene or paranaiphthalene, C 14 H 10 , which is found among the 
last products of the distillation of coal-tar, differs from naphthalene in 
being almost insoluble in alcohol, and fusing only at 415° F., whilst 
naphthalene fuses at 176° F.* 

Anthracene has been obtained by heating benzyle chloride with 
water ; 4C-H r Cl {benzyle chloride) = C 14 H 10 (anthracene) + C 14 H 14 ) diben- 
zyle) + 4HC1. 

Phenanthrene, C 14 H 10 , isomeric with anthracene, is contained in the 
portion of coal-tar which boils between 590° and 660° F. It is soluble 
in alcohol, and crystallises in colourless plates with a blue fluorescence. 
If it be dissolved in glacial acetic acid, and acted on by chromic acid, it 
yields phenanthraquinone C 14 H s 2 . 

Chrysene, C 1S H 12 , and pyrene, C 16 H 10 , are obtained at the close of the 
distillation of coal-tar ; they are crystalline solids not possessing any 
special importance, and have also been observed among the products of 
the destructive distillation of fatty and resinous bodies. 

Idrialene, C 22 H 14 , has been obtained from Idrialite, a mineral found in the mercury- 
mines of Idria. 

It is worthy of remark that pyrene C 16 H 10 contains more carbon than any other 
hydrocarbon (95 per cent.), and even more than is to be found in coal itself. 

Acridine, C ]2 H 9 N, is a crystallisable base found in crude anthracene and anthra- 
cene oils, which has a very irritating action on the skin. 

DESTKUCTIVE DISTILLATION OF WOOD. 

332. The destructive distillation of wood may be advantageously 
studied in order to gain an insight into the effects of heat upon organic 
substances comparatively free from nitrogen, just as that of coal may 
serve as a general illustration of the behaviour of nitrogenised bodies 
under similar treatment. 

The principal distinction between the two cases will be found to con- 
sist in the absence of basic substances from the products of the distilla- 
tion of non-nitrogenised bodies. 

Wood (freed from sap) consists of cellulose, vasculose (or lignine), and 
mineral substances or ash. The cellulose composes the wood cells and 
fibres, whilst the vasculose is the chief constituent of the vessels which 
bind them together. They may be separated by the action of solution of 
cupric oxide in ammonia, which dissolves the cellulose only. Vasculose 
is dissolved when heated with caustic alkalies under pressure, which is 

* The tar from Newcastle coal yields most anthracene, and that from cannel coal gives 
most paraffin. Much anthracene is now employed for the manufacture of alizarine. 



470 



PRODUCTS FROM WOOD. 



turned to advantage in preparing wood and straw for the manufacture 
of paper. It is also acted on by oxidising agents, such as chlorine-water 
and chloride of lime, which do not attack cellulose, but convert vasculose 
into resinous substances soluble in alkalies. The proportion of vasculose 
increases with the hardness and density of the wood. Poplar contains 
only 18 per cent, of vasculose, whilst iron- wood contains 40 per cent. 
The shells of nuts contain more vasculose in proportion to their hardness ; 
walnut shells contain 44 per cent, and cocoa-nut shells 58 per cent. 
Vasculose is always accompanied in the wood by resinous matters, giving 
rise to the differences of colour in woods, and by a small quantity of 
nitrogenised matter, and of ash deposited with it from the sap. 

The following results of the analysis of several woods will exhibit 
their general correspondence in composition : — 

Wood dried in vacuo at 284° F. 





Beech. 


Oak. 


Birch. 


Aspen. 


Willow. 


Carbon, ..... 
Hydrogen, .... 

Oxygen, 

Nitrogen, . . . ) 
Sulphur, . . . . ) 
Ash, 


49-46 

5-96 

42-36 

1-22 

1-00 


49-58 

5-78 

41-38 

1-23 

2-03 


50-29 

6-23 

41-02 

1-43 

1-03 


49-26 

6-18 

41-74 

0-96 

1-86 


49-93 

6-07 

39-38 

0-95 

3-67 


100-00 


100-00 


100-00 


100-00 


100-00 



Cellulose in a nearly pure condition constitutes cotton, linen, and the 
best kinds of (unsized) paper, since the processes to which the woody 
fibre is subjected in the preparation of these materials destroy and 
separate the less resistant lignine and the matters which accompany it. 

On comparing the composition of wood with that of coal, it will be 
obvious that the large proportion of oxygen in the former must give rise 
to a great difference in the products of destructive distillation. Accord- 
ingly, it is found that water, carbonic oxide, carbonic acid, and acetic 
acid, all highly oxidised bodies, are produced in large quantity, and that 
the gaseous products of the distillation of wood burn with far less light 
than those from coal, in consequence of the smaller proportion of the 
heavier hydrocarbons. 

The principal products of the action of heat upon wood are — 





Wood-Tar. 






Solids. 






Paraffin, 

Naphthalene, 

Cedriret, 


C x H 2ir +2 

C 10 H 8 
C 16 H ]6 6 




Pyrene, . 
Chrysene, 
Eesin, 


^16^10 

C 18 H 12 


Pittacal, 


C 25 H 26 9 1 








Liquids 






Toluene, 
Xylene, 


C 7 H 8 

C 8 H 10 




Pyroligneous or ) 
acetic acid, ) 


. C 2 H 4 2 


Cymene, 
Kreasote, 
Picamar, 


C 10 H 14 
. C 7 H 8 




Wood-naphtha, 
Methyle acetate, 
Methyle formiate, 


CH 4 

Clig. C9H.3O 

ch 3 .cho 2 


Kapnomor, . 
Eupioue, 


• C 10 H n O 

C 5 H 12 




Acetone, 
Water, 


C 3 H g O 



WOOD-NAPHTHA. 471 

Gases. 

Marsh gas, ....... CH 4 

Carbonic oxide, ...... CO 

Carbon dioxide, ...... C0 2 

Of these products, by far the most important are the pyroligneous acid, 
the wood-naphtha, and acetone. 

The distillation of wood with a view to the preparation of these sub- 
stances, is conducted in the manner described in the section on wood- 
charcoal (page 65), when the distillate separates into two portions, the 
heavier insoluble part constituting the wood-tar, whilst the light aqueous 
layer contains the pyroligneous acid, naphtha, and acetone. 

On distilling this, the two last, boiling respectively at 150° and 133° 
F., first distil over, and then the acetic acid, which boils at 243° F. The 
acid so obtained, however, is contaminated with tarry matters, which 
communicate the peculiar odour of wood smoke, and adapt it especially 
for the preservation of meat. In order to obtain pure acetic acid, this 
crude acid is neutralised with sodium carbonate, and the sodium acetate 
thus obtained is moderately heated to expel the foreign substances. It 
is then further purified by solution in water and crystallisation, and is 
distilled with sulphuric acid, which converts the sodium into sulphate, 
leaving the acetic acid to distil over.* 

333. Wood-naphtha — Methylic alcohol, H 3 C.OH. — In order to obtain 
the wood-naphtha (or pyroligneous ether, or u;ood-spirit, or pyroxylic 
spirit), the portion which distils over below 212° F. is rectified in a still 
containing chalk, which retains the acetic acid as calcium acetate. 

The wood-naphtha so obtained generally consists chiefly of methylic 
alcohol (CH 4 0), but contains also acetone, mpthyle acetate, and certain 
oily substances which impart to it a peculiar odour, and cause it to 
become milky when mixed with water. Wood generally yields about 
1 part of naphtha to 20 of acetic acid. In order to obtain the pure 
methylic alcohol, calcium chloride is dissolved to saturation in the crude 
wood-spirit, when a definite crystallisable compound is formed, of 4 
molecules of methylic alcohol and 1 of calcium chloride, CaCl 2 .4CH 4 0. 
This is heated in a retort placed in a vessel of boiling water, as long as 
any acetone and methyle acetate pass over, the above compound not 
being decomposed at 212° F. An equal weight of water is then added 
to the residue in the retort, and the distillation continued, when the 
methylic alcohol distils over, accompanied by water, and the calcium 
chloride remains in the retort. The diluted methylic alcohol is digested 
for some time with powdered quicklime, and again distilled, when it is 
obtained in a state of purity. 

The useful applications of crude wood-naphtha depend upon its 
burning with a nearly smokeless flame in lamps (though as a source 
of heat only, not of light), and upon its power of dissolving most 
resinous substances employed in the preparation of varnishes, stiffening 
for hats, &c. 

Methylic alcohol is the first member of the very important homologous 
series of alcohols of which ordinary alcohol or spirit of wine is the type 
(see page 437), and the consideration of which may be postponed until 
the chemical history of that alcohol shall have been studied. 

* In Condy's patent, advantage is taken of the formation of an easily crystallisable 
compound of calcium acetate with calcium chloride CaCl 2 .Ca(C 2 H 3 O 2 ) 2 .10Aq. 



472 PARAFFIN. 

One of the most interesting compounds derived from wood-spirit is 
the methyle salicylate or oil of winter green (CH 3 .C 7 H 5 3 ), which is 
extracted from the flowers of the Gaultlieria procumbens, and was one 
of the first vegetable products to be prepared artificially by the chemist. 
It is obtained by distilling wood-spirit with sulphuric acid and salicylic 
acid (HC 7 H 5 3 ), the latter acid being formed by the action of fused 
potash upon the salicine (C 13 H 18 7 ) extracted from willow bark. 

334. Paraffin (C 16 H 34 ) is a semi-transparent, waxy substance, which 
distils over with the last portions of the tar from wood, and may be 
obtained in larger quantity by distilling peat, as well as from the mineral 
known as Boghead cannel* and from bituminous shale. It is also found 
abundantly in the petroleum or mineral naphtha imported from Rangoon, 
and has lately been observed in small cavities in lava near Etna. 

In order to extract the paraffin from wood-tar, advantage is taken of 
its great resistance to the action of most chemical agents, t for which pur- 
pose the later portions of the distillate are moderately heated with con- 
centrated sulphuric acid, which decomposes and chars most of the sub- 
stances mixed with the paraffin, and allows the latter to collect as an 
oily layer upon the surface ; this is allowed to cool and solidify, when it 
may be purified by pressure between blotting-paper, and solution in a hot 
mixture of alcohol and ether, from which it is deposited, on cooling, in 
brilliant plates. 

When the oil from shale is re-distilled, the last portions of the distillate 
(heavy oil) contain much paraffin, which crystallises in scales as the oil 
cools. This is run into bags, which are squeezed by hydraulic pressure 
to remove the liquid portion, which is then artificially cooled to 20° E., 
when more paraffin crystallises out, and is purified by recrystallisation 
from naphtha, deodorised by blowing steam through it, and decolorised 
by animal charcoal, which is removed by filtration. 

Paraffin fuses at about 110° F., and may be distilled at a higher 
temperature; it burns, like wax, with a very luminous flame, and is 
employed as a substitute for wax in the manufacture of candles. It is 
insoluble in water, and dissolves sparingly in alcohol, ether being the best 
solvent for it. 

It has been shown by Thorpe and Young that when solid paraffin is 
strongly heated, under pressure, it is almost completely resolved into 
liquid hydrocarbons: from a specimen of paraffin fusing at 115° E, 
they obtained the following liquid members of the marsh-gas series ; 
C 5 H 12 , C 6 H 14 , C r H 16 , C S H 18 , C 9 H 20 , as well as several olefines (page 438). 

The substance known as paraffin oil, which is used for lubricating 
machinery, is the less volatile portion of the hydrocarbons formerlv 
obtained by the destructive distillation of Boghead cannel (found at 
Bathgate, near Edinburgh), and since that was worked out, from the 
bituminous shales of Linlithgow and Mid-Lothian. It is composed chiefly 
of heptylene, C 7 H 14 , and other hydrocarbons of the olefine series. The 
more volatile portion of the hydrocarbons so obtained is employed for 
illuminating purposes. 

Acetone will be described hereafter. 

01 the other products of the destructive distillation of wood enumerated at page 470 

* The kerosene shale of New South Wales resembles Boghead caunel in composition, 
f To which it OAves its name, from parum, little ; offinis, allied. 



PETROLEUM. 473 

some have been described amongst the products obtained from coal, and the remainder 
have been but little studied, and have not received any useful application. 

Eupione (ev-wicoi/, very fed) or pentane (C 5 H 12 ) is a liquid lighter than water, and 
boiling at 102° F. 

Kapuomor (Kairvbs, smoke, fxo7pa, a part) is an oily liquid, which boils at 360° F. 

Picamar (pix, pitch, amarus, bitter) is another oily liquid, heavier, than -water. 

Cedriret (cedria, pitch, rcte, a net, in allusion to its interlaced crystals) or coerulig- 
none, C 16 H l6 6 , is insoluble in ordinary solvents, but crystallises from phenole in blue 
needles. 

Pittacal (irirra, pitch, KaXbs, beautiful) is a blue solid. 

Hofmann has shown pittacal to be an acid {eupittonic acid H 2 C 25 H 24 9 ), and has 
prepared it from the crude dimethyl-ether of pyrogallol extracted from beech-wood 
tar. This ether is a mixture of dimethyle-pyrogallate C 6 (CH 3 ) 2 H(OH) 3 and di- 
methyle-methyle-pyrogallate C 6 (CH 3 )H 2 (OCH 3 )o()H. When these are heated with 
excess of soda, in contact with air, the latter removes hydrogen by oxidation, and 
pittacal is produced — 

2C 8 H 10 O 3 + C 9 H 12 G 3 = 3H 2 + C 25 H 26 9 . 

The sodium eupittonccte thus formed is dissolved in water, and the indigo-blue 
solution mixed with HC1, when it becomes carmine-red, and deposits a resinous body 
which yields crystals of eupittonic acid when purified. 

Stockholm tar is collected during the carbonisation of pine wood, con- 
taining a large quantity of resin, the tar running off through an aperture 
at the lower part of the pit, in which the imperfect combustion of the 
wood is carried on. It differs from ordinary tar in containing large 
quantities of resin and turpentine, the latter being separated from it by 
distillation, and the residue constituting the pitch of commerce. 

Petroleum. — There are found, in different parts of the earth, generally 
in or near the coal-formations, several solid or liquid hydrocarbons, pro- 
bably formed during the conversion of vegetable remains into coal, some 
of which have received useful applications. 

Bitumen is the name given to a number of these compounds of carbon 
and hydrogen. The chief solid variety is asphaltum or mineral pitcli, 
which resembles coal, but is easily fusible and dissolves in turpentine. 
It is abundant on the shores of the Dead Sea and in the island of Trini- 
dad. It is used for making the black varnish known as japan, and is 
mixed with limestone, &c, and cast into blocks for paving. Asphaltum 
contains oxygen as well as carbon and hydrogen. 

The Ban goon tar has already been noticed as containing a considerable 
quantity of paraffin ; the liquid part of this tar, after distillation and 
treatment with oil of vitriol to remove hydrocarbons of the benzene series,* 
is the liquid in which potassiuni and sodium are preserved; it is com- 
monly called petroleum or rock-oil, and appears to be a mixture of several 
hydrocarbons. Petroleum is also employed occasionally as a solvent for 
caoutchouc and resinous substances. In the neighbourhood of the Caspian 
Sea there are several springs from which rock-oil flows, together with water, 
from the surface of which it is skimmed and sent into commerce. 

The petroleum from the Caucasus contains hydrocarbons isomeric with 
the olefines (C n II 2n ), but more nearly resembling the paraffins in their 
chemical characters. 

American jietroleum. — Within the last few years abundant supplies of 
petroleum have been obtained from wells and springs in Pennsylvania 
and Canada, and the demand for it to serve as an illuminating agent, and 
for the lubrication of machinery, has created a new branch of commerce, 

* These hydrocarbons, when treated with oil of vitriol, form acids which are soluble in 
water. Thus benzene is converted into sulphobenzolic acid, HC 6 H 5 .S0 3 . 



474 OIL OF TURPENTINE. 

giving rise to the rapid growth of " oil cities " in the neighbourhood of the 
wells. These rock-oils have a very peculiar unpleasant odour, and appear 
to consist chiefly of hydrocarbons belonging to the homologous series of 
which marsh gas (CH 4 ) is a member. Thus, the Pennsylvanian petroleum 
has furnished the hydrocarbons, C 4 H 10 , C 5 H 12 , C 6 H 14 , C r ll 16 , C 8 H 18 ,* C 9 H 20 . 
Ethane C 2 H 6 has been found, together with marsh gas, among the gases 
contained in coal. In addition to these, the hydrocarbons, C 10 H 20 , C n H 20 , 
C l2 H 2i , homologous with olefiant gas (C 2 H 4 ), have been obtained from it. 
Some of the members of the benzene series appear also to be present in 
the Canadian petroleum. 

Those hydrocarbons which contain fewer than 6 atoms of carbon, boil 
at or below 100° F., and are separated from the petroleum (or kerosene or 
paraffin oil) intended for burning in lamps, as being dangerous on account 
of their volatility. Since each molecule of these hydrocarbons contains a 
large amount of combustible matter, a small volume of the vapour will 
render a large volume of air dangerously explosive. Thus, 2 vols, of 
pentane C 5 H 12 would confer explosive properties on more than 80 vols, of 
air, which would be required to supply the 16 atoms of oxygen for con- 
verting the C into C0 2 and the H into H0 2 . The more volatile naphthas 
have a specific gravity between - 67 and 0*69; the burning oils between 
0'8 and 0*81 ; the lubricating oils between # 86 and 0'9. The more 
volatile hydrocarbons are sold under the name of petroleum spirit, which 
is much used as a solvent, and is sometimes called kerosoline, or ligroine. 

Bituminous shale, when distilled, -furnishes products which, as far as 
they are known, are closely allied to those obtained from wood and coal. 

Ozokerite, or mineral tuax, is imported from Galicia, Hungary, and 
Russia, for the manufacture of candles. It contains 85 per cent, of carbon 
and 15 of hydrogen, and, when purified from an oil useful for illuminating 
purposes, consists of a group of solid hydrocarbons of the marsh gas series, 
melting at 140° F. 

Bog-butter, found in the Irish peat-mosses, is a similar body. Another 
mineral resembling this, found in New South Wales, contained 80 '6 per 
cent, C, 5-6 H, 5 -5 N", 1*6 O, and 6 '7 of ash. 

Vaseline is a soft substance belonging to the paraffin series, useful for 
lubricating purposes. 

Oil of Turpentine and Substances allied to it. 

335. Turpentine is the generic name given to the viscous exudation, 
obtained by incising the bark of various species of pine. Several varieties 
of turpentine are met with in commerce, of which the two best known 
are the common turpentine which is obtained from the Scotch fir, and 
Venice turpentine from the larch. 

These are both solutions of colophony or common resin (C 20 H 30 O 2 ) in 
the essential oil of turpentine (C 10 H 16 ), and when distilled, yield from 75 
to 90 per cent, of resin, which remains in the retort, and from 25 to 10 
per cent, of the essential oil, commonly sold as spirits of turpentine. 

This essence of turpentine boils at 320° F., and floats upon water (sp. 
gr. 0-864), in which it is very sparingly soluble, its proper solvents being 
alcohol and ether. Its great inflammability renders it useful as a fuel for 

* Heptane, C 7 H l6 , obtained by distilling the exudation of the Pinus sabiana or nut pine 
of California, is a remarkable example of a paraffin from the vegetable kingdom. It is 
used, under the name of Abietene, as a substitute for benzene in removing grease-spots, &c. 



OIL OF TURPENTINE. 475 

lamps, but the large proportion of carbon which it contains causes it to 
burn with a smoky name, rendering it necessary either to employ lamps 
constructed especially to afford an extra supply of air to the flame, or to 
mix it with a certain proportion of alcohol. Camphine is distilled from 
the turpentine of the Boston pine. 

The property of turpentine to dissolve resinous and fatty substances 
renders it exceedingly useful in the preparation of paints and varnishes, 
and for the removal of such substances from fabrics. • It is also an excel- 
lent solvent for caoutchouc. 

One of the most remarkable features of this essential oil is the facility with which, 
it changes into isomeric or metameric modifications, exhibiting great differences in 
their physical and chemical properties. 

When heated in a closed vessel to about 480° F. for some hours, oil of turpentine 
is converted into two isomeric modifications differing greatly from the original oil in 
the temperature at which they boil ; for whilst oil of turpentine distils over entirely 
at 320° F., one of these modifications, known as isoterebenthene, boils at 350° F., and 
the other, metatcrebenthene, at 660°. 

When digested, in the cold, with a small proportion of oil of vitriol, oil of turpen- 
tine yields terebene (C 10 H 16 ) and colophene, the former boiling at 320° F., but differing 
from oil of turpentine in its odour, which resembles thyme, and in its want of action 
upon polarised light. 

Colophene has a far higher boiling-point (600°), and is much heavier than turpentine 
(sp. gr. 0*940), from which it is also distinguished by its indigo-blue colour when seen 
obliquely, though it is colourless by directly transmitted light. Moreover, the specific 
gravity of the vapour of colophene is 9 '52, whilst that of turpentine is 4 76, or one- 
half that of colophene, rendering it probable that if the composition of turpentine be 
C 10 H 16 ( = 2 volumes) ; that of colophene is C 20 H ?2 ( = 2 volumes), a relation expressed 
by saying that colophene is polymeric with turpentine. Colophene is also obtained 
by the distillation of colophony. 

The ordinary oil of turpentine appears to be really itself a compound of two isomeric 
hydrocarbons, for when hydrochloric acid gas is passed into it, two distinct isomeric 
compounds are formed, both expressed by the formula C 10 H 16 .HC1, but one being a 
solid, and the other a liquid even at 0° F. 

The solid compound, which is known as artificial camphor or hydrochlorate ofdadyle, 
forms white prismatic crystals very similar to camphor, and when its vapour is passed 
over heated quicklime, the latter removes the hydrochloric acid, and the hydrocarbon 
known as caraphilcnc or daclylc (Ms, a pine-torch) is obtained, which is isomeric with 
oil of turpentine, but boils at 273° instead of 320° F., and is without any action upon 
polarised light. 

The liquid compound formed by the action of hydrochloric acid upon oil of tur- 
pentine is called hydrochlorate of peucyle ; and when distilled with quicklime yields 
tcrebilene ovpeucyle (irevKr), the pine), also isomeric with oil of turpentine, but without 
action on polarised light. 

Although oil of turpentine is not miscible with water, it is capable of forming 
three compounds with it in different proportions. When the oil is long kept in 
contact with water, crystals are deposited which have the composition C 10 H 16 .3H 2 O ; 
boiling water dissolves these, and deposits them in a prismatic form on cooling. 
The crystals fuse at about 217° F., and when further heated, lose a molecule of 
water, yielding another crystalline hydrate, which sublimes without alteration at 
about 480° F. When exposed to the air, this hydrate again absorbs a molecule of 
water. 

By distilling the aqueous solution of either of the preceding hydrates with a 
little sulphuric acid, a liquid hydrate smelling of hyacinths is obtained ; it contains 
(C 10 H 16 ) 2 HoO, and is called tcrpinole. 

When oil of turpentine is exposed to the air, it slowly becomes solid, 
absorbing oxygen, and becoming converted into resinous bodies. Among 
these bodies there is found a small quantity of camphoric peroxide, 
C 10 H 14 O 4 , which undergoes decomposition in contact with water, yielding 
camphoric acid and hydric peroxide ; C 10 H l4 O 4 + 2H 2 = C 10 H 16 O 4 + H 2 . 
This explains the observation that old oil of turpentine exhibits many of 



476 ESSENTIAL OILS. 

the reactions of hydric peroxide. By passing air and steam through oil 
of turpentine, a powerfully oxidising solution containing hydric peroxide 
has been prepared by Kingzett, and proposed, under the name of Sanitas, 
for disinfecting purposes. It is worthy of remark that the leaves of the 
Eucalyptus globulus (gum-tree of Australia), so much esteemed for its 
sanitary influence, also yield an oil similar to oil of turpentine, which 
becomes brown and resinous when exposed to air. 

Common resin or- colophony* — This substance is composed of two 
isomeric acids known as sylvic and pinic. When common resin is treated 
with cold alcohol, the greater portion of it is dissolved; and if the alcohol 
be evaporated, it leaves an amorphous substance, which is pinic acid. 
The residue, left undissolved by cold alcohol, is dissolved by hot alcohol, 
and deposited in colourless prisms, which are sylvic acid. These acids 
have the composition HC 20 H 29 O 2 . The pinate and sylvate of sodium 
obtained by dissolving resin in solution of soda or sodium carbonate, are 
largely used in the manufacture of yellow soap, and of the size for paper- 
makers. By distilling common resin with the aid of superheated steam, 
it is obtained nearly free from colour. 

336. The terpenes or turpentine series of hydrocarbons, C n H 2M ,_ 4 .— Oil 
of turpentine is the representative of a large class of hydrocarbons, derived 
like itself from the vegetable kingdom. All the individuals of this group 
resemble turpentine in their liability to suffer conversion into isomeric 
modifications, in their solidification by absorption of oxygen when exposed 
to the air, in their combination with water to form crystalline hydrates, 
and, above all, in their tendency to form artificial camphors by combining 
with hydrochloric acid. 

The oils of bergamotte, birch, camomile, carraway, cloves, hops, juniper, 
lemons, orange, parsley, pepper, savin, tolu, thyme, and valerian, contain 
the same hydrocarbon C 10 H 16 , generally accompanied, in the natural oil, 
by the product of its oxidation, bearing a relation to the hydrocarbon 
similar to that which colophony bears to turpentine. Essential oil of 
poplar is a di-terpene C 20 H S2 . 

These essential oils are generally extracted from the flowers, fruit, 
leaves, or seeds, by distillation with water, the portion of the plant 
selected being suspended in the still by means of a bag or perforated 
vessel, so that there may be no danger of its being scorched by contact 
with the hot sides of the still, and so contaminating the distillate with 
empyreumatic matters (i/xTrvpevo}, to scorch). The water which distils over 
always holds a little of the essential oil in solution, and it is in this way 
that the fragrant distilled waters of the druggist are obtained. When the 
essential oil is present in large proportion, it collects as a separate layer 
upon the surface of the water, from which it is easily decanted. The oil 
which is dissolved in the water may be separated from it by saturating 
the liquid with common salt, when the oil rises to the surface, or by 
shaking it with ether, which dissolves the oil and separates from the 
water, the ethereal solution floating upon its surface, and leaving the oil 
when the ether is evaporated. 

In eases like that of jasmine, where the delicate perfume of the flower 
would be injured by the heat, the flowers are pressed between woollen 

* Colophon, a city of Ionia, whence resin was obtained by the Greeks. 



BALSAMS— RESINS. 477 

cloths saturated with oil of poppy seeds, which thus acquires a powerful 
odour of the flower. 

Carbon disulphide is also sometimes employed as a solvent for extract- 
ing the essential oils. 

Oil of peppermint contains menthene (C 10 H 18 ), and menthole (C 10 H 20 O); 
essence of cedar-wood contains cedrene (C 16 H 26 ). 

337. Camphors. — Closely allied to the essential oils are the different 
varieties of camphor, which appear to be formed by the oxidation of 
hydrocarbons corresponding to the essential oils. 

Common camphor (C 10 H 16 O) is found deposited in minute crystals in 
the wood of the Laurus camphora or camphor laurel, from which it is 
obtained by chopping up the branches and distilling them with water in 
a still, the head of which is filled with straw, upon which the camphor 
condenses. It is purified by subliming it in large glass vessels containing 
a little lime. 

Camphor passes into vapour easily at the ordinary temperature of the 
air, and is deposited in brilliant octahedral crystals upon the sides of the 
bottles in which it is preserved. It fuses at 347° F., and boils at 399° F., 
and is very inflammable, burning with a bright smoky flame. It is some- 
times dissolved in the oil used for the lamps of magic lanterns, to increase 
its illuminating power. Camphor is lighter than water (sp. gr. 0"996), 
and whirls about upon its surface in a remarkable way, dissolving mean- 
while very sparingly (1 part in 1000), alcohol and ether being its appro- 
priate solvents. 

When distilled with phosphoric anhydride, camphor loses a molecule of water, and 
yields the hydrocarbon cymene (C 10 H U ) homologous with benzene. Cymene is found 
in the oil of wild thyme. 

Borneo camphor (C 10 H 18 O) is obtained from the exudation of the Dryobalanops 
camphora* When this exudation is distilled, a hydrocarbon called borneene (C 10 H 16 ), 
isomeric with oil of turpentine, first passes over, and afterwards the camphor, which 
is neither so fusible nor so volatile as ordinary camphor, and emits quite a different 
odour ; it also crystallises in prisms instead of octahedra, and may be converted 
into ordinary camphor by the action of nitric acid, which oxidises 2 atoms of 
hydrogen, C 10 H 18 O (Borneo camphor) - H 2 = C 10 H 16 O (Common camphor). 

The Borneo camphor appears to have been formed by the combination of borneene 
with water, for if this hydrocarbon be distilled with solution of potash, it combines 
with a molecule of water, and is converted into the camphor. On the other hand, 
when Borneo camphor is distilled with phosphoric anhydride, it loses a molecule 
of water, and yields borneene. It is interesting to remark that this hydrocarbon is 
also found in the essential oil of valerian. 

The oil of camphor, which accompanies the camphor distilled from the camphor 
laurel, contains an atom of oxygen less than common camphor, its formula being 
(Ci H 16 ) 2 O. 

338. Balsams. — The vegetable exudations known as balsams are mix- 
tures of essential oils with resins and acids probably produced by the 
oxidation of the oils. 

Balsam of Peru contains an oily substance termed cinnameine 
(C 2r H 26 4 ), a crystalline body, styracine (C 9 H 8 0), a crystalline volatile acid, 
the cinnamic (C 9 H s 0. 2 ), and a peculiar resin. 

Balsam of tolu also contains cinnamic acid and styracine, together 
with certain resins, which appear to have been formed by the oxidation 
of styracine. 

Storax, also a balsamic exudation, contains the same substances, accom- 

* The fragrant essence of lign-aloes has the same composition as Borneo camphor. 



478 RESINS. 

panied by a peculiar hydrocarbon, which has been named stymie, styrolent, 
or cinnamene, and has the composition C 8 H 8 . This liquid is characterised 
by a remarkable change which it undergoes when heated to about 400° F., 
being converted into a colourless solid, metastyrole, which is polymeric 
with styrole, into which it is reconverted by distillation. Styrole is also 
obtained by distilling dragon's blood with zinc-dust. 

339. Besins.- — Colophony is the best known member of the class of 
resins, which are generally distinguished by their resinous appearance, 
fusibility, inflammability, burning with a smoky flame, insolubility in 
water, and solubility in alcohol. 

As to their chemical composition, they are all rich in carbon and hydro- 
gen, containing generally a small proportion of oxygen, and appear to 
have been formed, like colophony (page 474), by the oxidation of a hydro- 
carbon analogous to turpentine- 
Most of the resins also resemble colophony in their acid characters, 
their alcoholic solutions reddening blue litmus paper, and the resins 
themselves being soluble in the alkalies. This is the case with sandarach 
and guaiacum resin, the former of which contains three, and the latter 
two, resinous acids. 

Copal appears to contain several resins, some neutral and some acid, 
and is distinguished by its difficult solubility in alcohol, in which it can 
be dissolved only after long exposure to the vapour of the solvent ; but 
if it be exposed to the air for some time, at a moderately high tempera- 
ture, it absorbs oxygen, and becomes far more easily soluble. Copal is 
readily dissolved by acetone. Animi and elemi resins are somewhat 
similar in properties to copal. AW these resins are used in the manu- 
facture of varnishes. 

Guaiacum resin is distinguished by its tendency to become blue under 
the influence of the more refrangible and chemically active (violet) rays 
of the solar spectrum, as well as under that of certain oxidising agents, 
such as chlorine and ozone. 

Lac, so much used in the arts, belongs to the class of resins, being the 
exudation of certain tropical trees punctured by an insect. In its crude 
natural state, encrusting the small branches, it is known as stick-lac, and 
has a deep red colour; when broken off the branches and boiled with 
water containing sodium carbonate, it furnishes a red colouring matter very 
largely used in dyeing, leaving a resinous residue termed seed-lac, by fusing 
which the shell-lac is obtained. This resin is very complex, containing 
several distinct resinous bodies. It is largely used in the manufacture of 
hats, of sealing-wax, and of varnishes. The lacquer applied to brass derives 
its name from this resin, being an alcoholic solution of shell-lac, sandarach, 
and Venice turpentine. Indian ink is made by mixing lamp-black with 
a solution of 100 grains of lac in 20 grains of borax and 4 ounces of water. 

Dragon's blood is a resin from a plant of the Lily tribe (Draccena 
draco) ; it gives a red solution in alcohol, which is used in lacquering. 

Amber, a fossil resinous substance, more nearly resembles this class of 
bodies than any other, and contains several resinous bodies. It is distin- 
guished by its insolubility, for alcohol dissolves only about one-eighth, 
and ether about one- tenth of it. After fusion, however, it becomes soluble 
in alcohol, and is used in this state for the preparation of varnishes. 

The distinguishing peculiarity of amber is, that it yields succinic acid, 
H 9 C 4 H 4 4 (succinum, amber), when digested with alkalies, distilled, or 



BENZOIC ACID. 



479 



oxidised by nitric acid ; in the latter case ordinary camphor is formed at 
the same time. 

Succinic acid is also found in some of the resins of coniferous trees, and 
in the leaves of the wormwood. As calcium succinate, it occurs as an 
exudation from the stems of mulberry-trees. It is among the products 
of the action of nitric acid upon most fatty and waxy substances, and is 
present in wines and other fermented liquors, being produced during the 
fermentation of sugar. The acid is characterised by the cough-provoking 
vapour which it emits when heated.* 

Varnishes are prepared by dissolving resins in alcohol, or wood- spirit, 
or acetone,! a little turpentine or some fixed oil being added to prevent the 
resin from cracking when the solvent has evaporated. In order to promote 
the solution of the resin, it is usually powdered before being treated with 
the solvent, and mixed with coarsely-powdered glass to prevent it from 
becoming lumpy. Methylated spirit is now very generally used for the 
preparation of varnishes ; it is simply 
spirit of wine, to which a little wood 
naphtha has been added, to deter 
persons from drinking it, and to pre- 
vent other frauds upon the Excise. 

Benzoin, or gum benzoin, as it is 
erroneously called, is also a vegetable 
resinous product, and is distinguished 
by the presence of benzoic acid 
(HC 7 H 5 2 ), which may be obtained 
from it by heating the resin in an 
iron or earthen vessel (fig. 281) 
covered with a perforated sheet of 
stout paper, over which a drum or cone 
of paper is tied. When the heat of a 
sand-bath is applied, benzoic acid rises in vapour, and is condensed in 
beautiful feathery crystals in the paper drum. It may also be extracted 
by boiling the resin with water and lime, when the benzoic acid is dis- 
solved in the form of calcium benzoate Ca(C 7 H 5 2 ) 2 , and being but 
sparingly soluble in water, may be precipitated by adding hydrochloric 
acid to the filtered solution. 

Benzoic acid is generally recognised by its feathery appearance and 
peculiar. agreeable odour, though this does not really belong to the acid, 
but to a little essential oil which is not easily separated ; the vapour of 
the acid itself is very irritating, and produces coughing. It fuses when 
moderately heated, and burns with a smoky flame. Benzoic acid dissolves 
in about 200 parts of cold and 25 parts of boiling water. Alcohol and 
ether dissolve it easily. 

The salts of benzoic acid, or benzoates, have no practical importance, 
but the behaviour of benzoic acid when distilled with an excess of lime 
or baryta has already been referred to as furnishing the important hydro- 
carbon, benzene (see page 468). 




Fig. 284. 



* Succinic acid has been obtained artificially by the action of potassium cyanide upon a 
solution of chloropropionic acid — 

C 3 H S C10 2 + KCN + 2H 2 = C 4 H 6 4 + KC1 + NH 3 
Chloropropionic. Succinic. 

f Acetone readily dissolves copal, mastic, and sandarach. 



480 OIL OF BITTER ALMONDS. 

Oil of Bitter Almonds and irs Derivatives. — Benzoyle Series. 

340. Benzoic acid results from the oxidation of the essential oil of 
bitter almonds (C 7 H 6 0), which slowly absorbs an atom of oxygen from 
the air, and is converted into benzoic acid (C 7 H 6 2 ). 

The formation of the essential oil of bitter almonds is one of the most 
interesting processes of vegetable chemistry. 

Both the bitter and the sweet almond contain a large quantity of a 
fixed oil, which may be extracted from them by pressure, but which has 
no particular taste or odour, and differs entirely from the essential oil of 
bitter almonds, being, in fact, very similar to ordinary olive oil. The 
residue, or almond-cake, which is left after expressing the oil, contains, in 
the case of the bitter almond only, a bitter principle, amounting to about 
2^th of the weight of the almond, which may be extracted from the cake 
by hot alcohol, and may be crystallised from the solution; this substance 
is called amygdaline, and is represented by the formula C^H^jSTOh, the 
crystals containing, in addition, 3 molecules of water. 

Now, if the residue left after extracting the amygdaline with alcohol 
be mixed with water and distilled, it does not yield any essential oil, 
although this may be obtained in abundance from the original cake after 
maceration in water, particularly if it be digested with water for several 
hours before distillation. 

The sweet almond, which contains no amygdaline, does not afford any 
essential oil when distilled with water, showing that the amygdaline is 
really the source of the essence. Again, if boiling water be poured over 
the bitter almond cake, no essential oil is produced, even when the mix- 
ture is allowed to stand for some time, but if to this mixture there be 
added an emulsion of sweet almonds prepared with cold water, the bitter 
almond oil is at once formed, which is not the case, however, if the emul- 
sion be prepared with boiling water. 

From this it is evident that a substance exists in both sweet and bitter 
almonds which is capable of developing the essence from the amygdaline 
contained in the latter, but which loses its power when acted upon by 
hot water. This may be still further proved by dissolving pure amygda- 
line in water, and adding an emulsion of sweet almonds, when the essence 
is at once produced. 

When the emulsion of sweet almonds is filtered and mixed with alcohol, 
a white substance resembling albumen is precipitated, which contains 
carbon, hydrogen, nitrogen, and oxygen, and very easily putrefies when 
exposed to the air in a moist state. If this substance, which is called 
emulsine or synaptase (a-vvdirTM, to bring into action), be dissolved in cold 
water, and mixed with a solution of amygdaline, the oil of bitter almonds 
is soon formed in abundance, but if the solution of emulsine be boiled, it 
is no longer capable of developing the essence. On examining the solu- 
tion of amygdaline in which the essential oil has been produced by the 
action of emulsine, it is found to contain, in addition, hydrocyanic acid 
(CHIsT), grape-sugar (C 6 H 14 7 ), and formic acid (CH 2 2 ), so that the 
decomposition may be thus represented — 

2C 20 H 97 NO n = 4C 7 H fi O + 2CHN + C 6 H 14 7 + 4CH 2 2 + 3H 2 0. 

Amygdaline. Blttajhmmd Hydrocyanic Gmpe gugar _ Formicacidt 

The formation of the essential oil of bitter almonds must be regarded, 
therefore, as dependent upon a species of fermentation or metamorphosis 



BENZOYLE SERIES. 481 

of the bitter principle amygdaline, induced by contact with, an albuminous 
substance, emulsine, itself very prone to undergo decomposition when 
exposed to air in the presence of moisture. 

This essential oil may also be obtained from laurel leaves, and from the 
kernels of most stone fruit. 

When the oil of bitter almonds is distilled over, it is accompanied by 
the hydrocyanic acid formed at the same time, and it is this which 
renders the ordinary commercial oil so powerful a poison, for if it be 
purified by distillation with a mixture of lime and ferrous chloride (see 
Prussian blue), which retains the hydrocyanic acid, it becomes compara- 
tively harmless. A better process for obtaining the pure oil of bitter 
almonds consists in shaking the crude oil with an equal volume of a 
strong solution of hydrosodic sulphite (XaHS0 3 ), "with, which it forms a 
white crystalline compound. If this be distilled with solution of sodium 
carbonate, the pure oil passes over. 

The poisonous properties of laurel-water, and similar preparations, are 
also due to the presence of hydrocyanic acid. 

The crude essential oil of bitter almonds also contains a ciystalline substance called 
bcnzoine (C u H 12 2 ), which is interesting as being polymeric with the essence, into 
which it may be converted by passing its vapour through a red hot tube. The crude 
oil may be entirely converted into this substance by shaking it with an alcoholic 
solution of potash. 

When the pure essential oil of bitter almonds (C 7 H 6 0) is acted upon by dry 
chlorine, it evolves hydrochloric acid, and becomes converted into a colourless liquid, 
having an odour of horse-radish, and containing C 7 H 5 C10, an atom of hydrogen 
having been removed, and its place filled by an atom of chlorine. If this liquid be 
acted upon by the bromides, iodides, cyanides, or sulphides of the metals, the 
chlorine is removed in its turn, the vacancy beiDg filled up by bromine, iodine, 
cj T anogen or sulphur, compounds being obtained which have the formulae — 

C 7 H 5 Br0, C 7 H 5 IO, C 7 H 5 CyO, (C 7 H 5 0) 2 S . 

When boiled with water, this chlorine compound is converted into benzoic acid — 

C 7 H 5 C10 + HoO = C 7 H 5 2 .H + HC1. 

On comparing the composition of these compounds with that of the essential oil 
from which they are derived, our attention is called to the existence of C 7 H 5 in 
all of them — 

Oil of bitter almonds, . (C 7 FT 5 0)H - 

Benzoic acid, . . . (C 7 H 5 0)HO 

Chlorine compound, . (C 7 H 5 0)C1 

Bromine „ . . (C-H 5 0)Br, &c. 

This circumstance led many chemists to assume the existence in these compounds 
of the radical benzoyle (C 7 H 5 6), capable of playing the part of an elementary sub- 
stance in uniting with oxygen, chlorine, &c. , and therefore resembling the elements 
in its chemical tendencies, from which resemblance it is spoken of as a quasi-element 
or compound radical. 

The radical benzoyle itself has been recently obtained in a separate state by the 
action of sodium on benzoyle chloride. It forms prismatic crystals, which fuse 
easily, and may be sublimed without decomposition. They are sparingly soluble in 
alcohol and ether. The formula C 7 H 5 should be doubled to express correctly, a 
molecule of this radical (see Alcohol radicals). 

It will be noticed that benzoic anhydride is not included in the above enumeration 
of the benzoyle series. This compound, which may be represented as Bz 2 0, or 
(C-H 5 0) 2 0, is obtained by heating sodium benzoate with benzoyle chloride — 

NaBzO + BzCl = XaCl + Bz 2 . 

This substance has no acid properties whatever. It does not dissolve in cold water, 
but if boiled with water, is slowly converted into benzoic acid. 

AVhen oil of bitter almonds is decomposed by potassium hydrate dissolved in 
alcohol, it yields benzoic alcohol (C 7 H 8 0), which will be more particularly noticed: 

2h 



482 GLUCOSIDES. 

hereafter. "When heated with strong hydriodio acid, bitter almond oil is converted 
into toluene C 7 H 8 . 

341. Very closely connected with the essential oil of bitter almonds are the essences 
of cinnamon and cassia, which consists chiefly of an oxidised essence, represented 
by the formula C 9 H 8 0, and convertible by boiling with nitric acid into the essence 
of almonds. By heating the essence of cinnamon with caustic potash, it is oxidised 
and converted into potassium cinnamate — 

C 9 H 8 {Oil of cinnamon) + KHO = KC 9 H 7 0. 2 (Potassium cinnamate) + H 2 . 

On dissolving this salt in water, and adding an acid, the cinnamic acid is precipi- 
tated in feathery flakes, closely resembling benzoic acid, both in appearance and 
chemical characters.* 

The same reasons exist as in the case of the benzoyle series, for assuming the 
existence, in the compounds derived from oil of cinnamon, of the radical cinnamylc, 
C 9 H 7 0, so that the oil of cinnamon would be cinnamyle hydride (C 9 H 7 0)H, and 
cinnamic acid the cinnamyle hydrate (C 9 H 7 0)HO. 

Essential oil of cumin is a mixture of the hydrocarbon cymene (C 10 H 14 ), which has 
been already noticed, with an oxidised essence, C 10 H 12 O, which is closely analogous 
to those of almonds and cinnamon, and is called cumyle hydride (C 10 H n O)H ; when 
acted upon by oxidising agents it yields cuminic acid (HC 10 H n O 2 ), which resembles 
benzoic acid, but is characterised by an odour similar to that of the bug. From 
cumyle hydride an oily compound has been obtained, which is polymeric with the 
supposed radical cumyle, having the composition C 20 H 22 O 2 , and that it is really com- 
posed of a double molecule of that radical is rendered very probable by its behaviour 
when fused with potash, its hydrogen converting one molecule of cumyle into cumyle 
hydride, whilst its oxygen converts the other into cuminic acid; C„ H 2O O o + KHO 
= (C 10 H 11 O)H + K(C 10 H 11 O)O. 

The essential oils of aniseed, fennel, and tarragon contain, in addition to a hydro- 
carbon isomeric with turpentine, a solid crystalline oxidised essence (C 10 H 12 O) 
isomeric with cumyle hydride. That this substance is not cumyle hydride, however, 
is at once proved by the action of oxidising agents, which convert it into anisyle 
hydride (C 8 H 7 2 )H, and anisic acid HC 8 H 7 3 , the latter being isomeric with winter- 
green oil (see page 472). 

342. Salicine and its Derivatives — Glucosides. — Oil of spirma, or 
meadow siveet, consists chiefly of the compound (C 7 H 6 2 ) isomeric with 
benzoic acid; this compound is easily obtained artificially by the oxida- 
tion of salicine, a bitter substance extracted from willow bark, by boiling- 
it in water, removing the colouring matter and tannin from the solution 
by boiling with lead hydrate, precipitating the excess of lead by hydro- 
sulphuric acid, and evaporating the filtered liquid, when the salicine 
crystallises out, and may be obtained, by recrystallising from alcohol, in 
beautiful white needles having the composition C 13 H 18 7 . 

Salicine is sparingly soluble in cold water and insoluble in ether, but 
dissolves readily in boiling water and in alcohol. It is readily distin- 
guished by the red colour which it gives with concentrated sulphuric acid, 
which manifests its presence when applied to the inner bark of the willow. 
When distilled with dilute sulphuric acid and potassium dichromate, it 
yields the oil of spiraea. 

The changes suffered by salicine when boiled with a dilute mineral acid (as sul- 
phuric) are very remarkable, for after the boiliug has been continued for a few 
minutes, the solution is found to contain grape-sugar, together with a crystalline 
substance called saligenine, which is distinguished by the intense blue colour which 
it gives with ferric chloride. The change is easilj" explained, for the addition 
of 2 molecules of water to salicine would provide the elements of grape-sugar and 
saligenine ; C 13 H 18 7 + 2H 2 = C 7 H s 2 + C fi H 14 7 . 
Salicine. .Saligenine. Grape -*u£ar. 

Emulsine or synaptase is capable of effecting this change in salicine, and it will 
be remembered that grape-sugar is one of the products of the action of that ferment 

* Oil of bitter almonds has been converted into cinnamic acid by heating it with acetic 
oxychloride ; C 7 H 6 + (C 2 H 3 0)Cl=C 7 H 3 (CoH 3 0)0 + HCl. 



SALICYLE SERIES. 483 

upon amygdaline. If the ebullition of the diluted acid be continued for a length 
of time, the liquid deposits a resinous substance, saliretine, which is isomeric with 
oil of bitter almonds (C 7 H 6 0). 

A very striking example of the stability of types, notwithstanding the substitution 
of one element for another, is found in the circumstance that salicine, under the 
influence of chlorine, yields three different products containing chlorine in place 
of hydrogen, and that when these are boiled with dilute acids, they yield other 
products containing chlorine, and bearing the same relation to their chlorinated 
primitive which saligenine and saliretine respectively bear to salicine. 

Thus we have — 



Salicine, . . . 


• C 13H 18 07 


Saligenine, . ... 


• C 7 H 8 2 


Chlorosalicine, . 


• c ^fjo 7 


Chlorosaligenine, . . 


• C7 ci 7 ( ° 2 


Dichlorosalicine, 


• c «ci' 2 6 |°' 


Dichlorosaligenine, 


. c 7 ^jo 2 


Trichlorosalicine, 


■ c «cirK 


Trichlorosalagenine, 


• ^jo 2 



When salicine is fused with potassium hydrate, the mass dissolved in water, and 
hydrochloric acid added, beautiful needles of salicylic acid (HC 7 Hg0 3 ), are separated. 
This acid may also be obtained from the oil of spiraea by a similar process, and it 
will be seen that salicylic acid bears the same relation to this oil as benzoic acid bears 
to oil of bitter almonds — 

Oil of bitter almonds, C 7 H 6 | Oil of spiraea, . . C 7 H 6 2 
Benzoic acid, . . C 7 H 6 2 | Salicylic acid, . . C 7 H 6 3 . 

Salicylic acid has been found in the leaves, stems, and rhizomes of some of the 
Violacece. 

Salicylic acid is now prepared from phenole (carbolic acid) ; one molecular weight of 
crystallised phenole is dissolved in a strong solution of one molecular weight of sodium 
hydrate; C 6 H 5 OH + NaOH = C 6 H 5 ONa + HOH. The resulting solution of sodium- 
phenole is evaporated to complete dryness, the solid transferred to a retort, heated to 
100° C. , and a slow stream of C0 2 passed over it, the temperature being raised, after 
many hours, to 180° C. Phenole then distils over, and continues to do so till the 
temperature has risen to 250° C, when di-sodium salicylate remains in the retort ; 
2C 6 H 5 ONa + C0 2 = C 7 H 4 Na 2 3 + C 6 H 5 0H. 

The sodium salt is dissolved in water and decomposed by hydrochloric acid, when 
the salicylic acid is precipitated. 

On account of its easy decomposition into C0 2 and phenole, salicylic acid has been 
recommended as an antiseptic, since it is inodorous, nearly tasteless, and not poison- 
ous in moderate doses.* 

Salicylic acid is an example of a monobasic diatomic acid. .It forms two sodium 
salts, Na. 2 C 7 H 4 3 and NaC 7 H 5 3 . But the constitution of salicylic acid is C 6 H 4 .OH. 
COOH, showing that it contains only one oxatyle group (COOH) upon which the 
basicity of an acid depends. Hence the normal sodium salicylate is C 6 H 4 . OH. COONa, 
and the salt containing Na 2 is a basic salt, C 6 H 4 . ONa. COONa. 

Lactic acid, C 2 H 4 . OH. COOH, is another example of the same kind, the normal sodium 
lactate being C 2 H 4 .OH.COONa, and the di-sodium salt C. 2 H 4 .ONa.COONa. 

Exactly as chemists have been led to consider the bitter almond oil as benzoyle 
hydride, so they have regarded oil of spiraea as salicylc hydride (C 7 H 5 2 .H), assum- 
ing the existence of the radical salicylc (C 7 H 5 2 ), of which salicylic acid would be 
the hydrate. We find this view of the constitution of these compounds supported by 
the circumstance, that when the oil of spiraea is heated with benzoyle chloride, a sub- 
stance is obtained which may be regarded as composed of the two radicals salicyle 
and benzoyle ; C 7 H 5 2 . H + C 7 H 5 0. CI = C 7 H 5 0. C 7 H 5 2 + HC1. 
Oil of spiraea. chloride 6 Benzoyle-salicyle. 

From a careful study of the behaviour of salicine under the action of various re- 
agents, the inference has been drawn that it is a compound of saligenine (C 7 H 8 2 ) 
with a substance (C 6 H 10 O 5 ) which becomes converted into grape-sugar, by assimila- 
tion of water, as soon as it is separated from the saligenine. 

Salicine is occasionally employed in medicine as a febrifuge, and is a 
common adulteration of quinine. 

* Much of the commercial salicylic acid consists of sodium salicylate. 



484 CONIFERINE — VANILLINE. 

Salicine is the chief member of the class of substances termed gluco- 
sides, from the presence of grape-sugar (glucose) among their products of 
decomposition. To this class belong several other substances much re- 
sembling salicine, and, like it, extracted from the barks of different trees. 

Conifcrine, C 16 H 2 . 2 8 .2Aq., is a crystalline glucoside contained in the glutinous 
liquid {cambium) found in spring between the inner and outer barks of coniferous 
trees. With strong sulphuric acid it gives a violet colour changing to red, the red 
solution depositing a blue resin on addition of water. When heated with diluted 
acids, it yields glucose and a resinous substance. If coniferine be kept in contact 
with water and a little emulsine (p. 480) at a temperature of 170° to 190° F., it splits 
up into glucose and a white crystalline precipitate which dissolves on shaking with 
ether, and may be obtained by evaporating the ethereal solution. This substance has 
the formula C 10 H 1 . 2 O 3 , and its formation from coniferine is expressed by the equation — 

C lfi H,,O s + H 2 = C 6 H 12 6 + C 10 H 12 O 3 . 
Coniferine. Glucose. 

When the crystalline body is exposed to the air it exhales the odour of vanilla. 
On distilling it with potassium dichromate and sulphuric acid, aldehyde passes over, 
followed by an aqueous liquid from which ether extracts a crystalline body having the 
composition C 8 H 8 3 , and identical with vanilline, which constitutes the aroma of 
vanilla, and is often seen covering the surface of vanilla-pods with small crystals. 

The conversion of the product of the fermentation of coniferine into vanilline is 
represented thus ; C 10 H 12 O 3 + O = C 2 H 4 O {aldehyde) + C 8 H 8 3 {vanilline). 

Vanilline fuses at 176 D F., and sublimes unchanged. It was formerly mistaken for 
benzoic acid, for it is sparingly soluble in water, but readily soluble in alcohol and 
ether. It is also strongly acid, and forms well-defined salts.* 

The artificial production of vanilline from so abundant a source is of considerable 
importance, since vanilla-pods are imported into this country at a high price from 
Mexico, being the seed-vessel of an orchidaceous plant {Vanilla planifolia). 

Coumarine, C 9 H r) 2 , is the substance which causes the smell of hay and of the 
Tonka bean (Coumaroma odorata), from which it may be extracted by boiling with 
alcohol, when crystals of coumarine are deposited on cooling. It has been obtained 
artificially from the oil of meadow sweet, salicyle hydride, by treating it with sodium, 
and decomposing the sodium-salicylide with acetic anhydride — 

N"aC 7 H ? 2 + (C,H 3 0) 2 = NaC 2 H 3 2 + C 2 H 3 0. C 7 H,0 2 ; 

Sodium saiicylide. Acetic anhydride. Sodium acetate. Acetyle-salicylide. 

andC 2 H 3 O.C 7 H 5 2 = H 2 + C 9 H 6 2 

Coumarine. 

343. Populine (C. 20 H 22 O 8 ) is a sweet crystalline substance obtained from the bark 
and leaves of the aspen, and especially interesting from its close connexion with the 
benzoyle and salicyle series ; for when boiled with solution of baryta, it is decom- 
posed into benzoic acid and salicine — 

2C, H,. 2 O 8 + Ba(HO) 2 = Ba(C 7 H 5 2 ) 2 +2C ]3 H 18 7 
Populine. Barium benzoate. Salicine. 

Nor is this the only connecting link, for populine yields oil of spireea when distilled 
with sulphuric acid and potassium dichromate, and when boiled with dilute acids it 
furnishes benzoic acid, saliretine, and grape-sugar — 

C 20 H 22 O 8 + 2H 2 = HC 7 HA + CyH.O + C 6 H 14 7 

Populine. Benzoic acid. Saliretine. Grape-sugar. 

In order to explain this production of benzoyle and salicyle compounds from populine, 
it is usual to regard this substance as formed from salicine (C 13 H 18 7 ) by the introduc- 
tion of benzoyle (C 7 H 5 0), in the place of an atom of hydrogen — 

C 20 Ho 2 O 8 = C 13 H 17 (C 7 H 5 0)0 7 

Populine. Benzoyle-salicine. 

Phloridzine (C 21 H 24 O 10 ) is extracted from the bark of the apple, pear, plum, and 
cherry tree ; it crystallises readily, is slightly bitter, and when boiled with dilute 
acids, yields grape-sugar and a resinous substance called phloretine (C 15 H 14 5 ). Its 

* For further information respecting the constitution and structural formula of vanilline, 
see Proceedings of the Royal Society, xxii. p. 398. 



ALLYLE SEEIES. 485 

most interesting property is that of forming a red compound {phloridzeine) when 
exposed to the joint influences of air and ammonia — 

C 21 H 24 O 10 [Phloridzine) + 3 + 2NH 3 = C 21 H 30 N 2 O 13 (Phloridzeine). 

This red compound combines with ammonia to form a purple mass with a coppery 
lustre, which dissolves in water with a fine blue colour. The production of this 
colouring matter from phloridzine is an excellent example of that conjoined action of 
air and ammonia by which certain natural colouring matters, such as litmus, are 
formed from substances which are themselves destitute of colour. 

Quercitrina (C 33 H 30 O 7 ) is the yellow colouring matter extracted by alcohol from 
the bark of the quercitron. It is a crystallisable substance, and is decomposed by 
boiling with acids into grape-sugar and a yellow crystalline body called qucrcetine 
(C 27 H 18 12 ). 

Esculine (C 21 H. 24 13 ) is extracted from the bark of the horse-chestnut by boiling 
water. If the tannin and colouring matter be precipitated from the infusion by 
lead acetate, the filtered liquid treated with hydric sulphide to remove the excess of 
lead, and the solution, after a second filtration, evaporated, the esculine is obtained 
in colourless needles. It is remarkable for its fluorescence ; although its solution is 
colourless by transmitted light, it appears of a beautiful deep blue colour when 
viewed at certain angles. This substance is also a glucoside, for when boiled with 
dilute acids, it yields grape-sugar and a crystalline substance known as esculetine ; 
C 2 iH 24 13 + 5H 2 = C 9 H 6 4 + 2C 6 H U 7 . 
Esculine. Esculetine. Grape-sugar. 

Paviine also occurs in the horse-chestnut bark, but in a far larger quantity in the 
bark of the ash. It is distinguished from esculine by exhibiting a green fluorescence. 

Hesperidine, C 22 H 26 12 , is contained in the fruit,leaves, and stalks of the orange-tree 
and other members of the same family ; it is resolved by acids into glucose and 
liesperctine, C 16 H 14 6 . 

Saponine is a substance closely allied to the glucosides, and is found in the soap- 
wort, the fruit of the horse-chestnut, the pimpernel, the root of the pink, and in 
many other plants. It may be extracted by boiling alcohol, which deposits it in an 
amorphous state on cooling. Saponine is soluble in water, and its solution is char- 
acterised by the readiness with which it lathers, like soap and water, although it 
may contain a very small quantity of saponine. This property leads to the use of 
decoctions containing it, such as those of the soap-wort and of the soap-nut of India, 
for the purpose of cleansing certain delicate fabrics. 

Picrotoxine (C 36 H 40 O 16 ) is a crystalline substance, to which the poisonous properties 
of Cocculus indicus are due. It appears to have feeble acid tendencies, and is ex- 
tracted from an acidified solution by shaking with ether. On evaporating the ethereal 
solution it leases prismatic needles of an intensely bitter taste. 

344. Essential Oils containing Sulphur — Allyle Series. — The 
essential oils of asafoetida, of garlic, horse-radish, leeks, mustard, onions, 
and radishes, differ from those which have been already described by 
containing sulphur. 

Those of asafoetida, garlic, leeks, onions, and radishes are composed 
essentially of the same substance, represented by the formula C 6 H 10 S. 
The essence of mustard and that of horse-radish are composed of C 4 H 5 NS. 

The chemistry of the origin of essential oil of mustard is analogous to 
that of essence of almonds. The oil is obtained from the seeds of the 
black mustard after removing the fixed oil (which has no pungency 
whatever) by pressure ; on moistening the crushed seed with water, the 
production of the essential oil is indicated by its peculiar odour, and it 
may be separated from the seeds by distillation. The mustard seeds 
contain a salt of potash with a peculiar acid called myronic acid* 
(HC 10 H 18 NS 2 O ]0 ), together with a substance similar to the emulsine of 
almonds, which has been termed myrosine, and is capable of inducing the 
decomposition of the myronic acid, and the consequent production of 
essence of mustard, just as the emulsine of almonds develops the essential 
* From ixvpov, an unguent.- 



486 ALLYLE SEKIES. 

oil by the decomposition of the amygdaline ; in the ease of mustard, how- 
ever, the nature of the decomposition has not been so clearly made out, 
but is probably represented by the equation — 

KC 10 H 18 NS 2 O 10 = C 4 H 5 XS + C 6 H 12 6 + KHS0 4 . 

Potassium myronate. ^SSrf* Glucose. 

The essence of mustard has been produced artificially in a very inter- 
esting and remarkable manner. 

When glycerine (the sweet principle of the fats and fixed oils) is dis- 
tilled with iodine and phosphorus, a colourless ethereal liquid is obtained, 
which has the composition C 3 H 5 I, and is called allyle iodide, because, 
when distilled with sodium, it yields sodium iodide and a volatile 
liquid composed of (C 3 H 5 ) 2 and called di-allyle, in allusion to its peculiar 
odour (allium, garlic). The formation of allyle iodide is explained by 
the following equation; 2C 3 Hg0 3 + 2PI 2 = 2C 3 H 5 I + 2H 3 P0 3 + 1 2 . 

Glycerine, Allyle iodide. 

When allyle iodide is distilled with potassium sulphocyanide, an oily 
liquid is obtained, identical in properties and composition with oil of 
mustard or allyle sulphocarbimide* its artificial production being thus 
explained ; C 3 H 5 I + K(CNS) = KC 3 H 5 .CS + KI. 

.,, , . r , Potassium Allyle sulphocarbimide, 

Aiiyie loaiae. sulphocyanide. or oil of mustard. 

Additional interest is created in this artificial formation of oil of mus- 
tard when it is found to be convertible into oil of garlic, by being heated 
with potassium sulphide, when potassium sulphocyanide is formed at the 
same time, thus; 2(KC 3 H 5 .CS) + K 2 S = (C 3 H 5 ). 2 S + 2K(CNS) 

Essence of mustard. Essence of garlic. su ^cyaZle. 

Hence it is inferred that the essence of garlic is allyle sidphide. 

The oil of Coclilearia officinalis (scurvy-grass) is sometimes sold as 
essential oil of mustard, which it much resembles ; but the former is 
butyle sulphocyanide C 4 H 9 .CNS, and boils at 160° G, whilst the latter 
boils at 147° C. 

A considerable number of compounds are included in the allyle series, but are not 
at present possessed of any practical importance. 

The allylic alcohol (C 3 H 5 HO) is interesting as the prototype of a new class of 
alcohols, parallel with that represented by common alcohol (C. 2 H 5 HO). In order to 
obtain it, allyle iodide is decomposed by silver oxalate, when allyle oxalate is obtained ; 
2C 3 H 5 I + Ag 2 C 2 4 =(C 3 H 5 ) 2 C 2 4 + 2AgI. < 

By treating allyle oxalate with ammonia, allylic alcohol and oxamide are obtained ;~ 
(C 3 H 5 ) 2 C 2 4 + 2NH 3 = 2C 3 H 5 HO + C 2 H 4 N 2 2 . 
Allyle oxafate. Aliyiic alcohol. Oxamide. 

* A sulphocarbiinide is metameric with a sulphocyanide ; but in the latter, the alcohol 
radical is combined with the sulphur, whilst, in the former, it is combined with the 
nitrogen. Thus, ethyle sulphocyanide, decomposed by potassium hydrate, yields potassium 
sulphocyanide and ethyle hydrate (alcohol) — 

But ethyle sulphocarbimide yields ethylamine, potassium carbonate and potassium 
sulphide — 

N { CS* 5 + 40 { H = N | Sf 5 + KaC °3 + K2S + H 2°- 

The name sulphocarbimide alludes to the hypothetical body HNCS (metameric with 
hydric sulphocyanide) ; the termination imicle being often applied to bodies in which a 
single atom of H is united to N. 



GUM-RESINS. 487 

Allyle -alcohol is also found among the products of the distillation of glycerine with 
oxalic acid. 

Allylene (C 3 H 4 ), the oleflant gas of the allyle series, is homologous with acetylene, 
(C 2 H 2 ), and much resembles it in its chemical relations. It has been prepared by 
heating chlorinated propylene in a sealed tube with sodium-alcohol. The chlorin- 
ated propylene is a product of the action of phosphoric chloride upon acetone ; 
C 3 H 6 (Acetone) + PC1 5 = C 3 H 5 C1 (Chlorinated propylene) + PC1 3 + HC1 ; 

C 3 H 5 Cl + C 2 H 5 XaO (Sodium-alcohol) =C 3 H 4 U%^) + NaCl + C 2 H 6 (Alcohol). 

By its action on ammoniacal silver nitrate, it yields argentallylene, C 3 H 3 Ag. 
"When sodium is heated in allylene, carbon and hydrogen are liberated, and sodic 
acetylide is formed, C 3 H 4 + Na 2 = C 2 Na 2 + + H 4 , a little propylene (C 3 H 6 ) is formed 
at the same time. 

By heating diallyle tetrabromide (C 6 H 10 Br 4 ) with alcoholic potash, cliprojmrgyle 
(C 6 H 6 ) is obtained, a liquid having the same composition as benzene, but boiling at 
85° C. , whilst benzene boils at 80°. 

345. Gum-resins.- — The gum-resins consist of a mixture of gum with 
resin, and occasionally with essential oil, and are distinguished by their 
behaviour when triturated with water, which dissolves the gum and leaves 
the oil and resin suspended, giving the liquid a milky appearance. They 
also differ from most resins in being only partially soluble in alcohol The 
gum-resins exude from the plants producing them in a milky state, 
gradually solidifying by exposure to the air. 

Asafcetida contains a resin of the composition C 20 H 26 O 5 , and owes its 
powerful odour to an essential oil containing sulphur, which has been 
already noticed. Galbanum, ammoniacum, aloes, olibanum or frankincense, 
scammony, gamboge, myrrh, and euphorbium, also belong to the class of 
gum- resins. 

Caoutchouc (C 5 H 8 ) is so far allied to the gum-resins, that it is procured 
from a milky exudation furnished by several tropical plants, particularly 
by the Hcevcea guianensis and Jatropha elastica. Incisions are made in 
these trees, and the milky liquid thus obtained is spread upon a clay 
bottle-shaped mould, which is then suspended over a fire ; a layer of 
caoutchouc is thus deposited upon the mould, and its thickness is after- 
wards increased by repeated applications of the milky liquid, the mould 
being eventually broken out of the caoutchouc bottle thus formed. The 
dark colour of the caoutchouc found in commerce is believed to be due 
to the smoke from the fire over which it is dried, for pure caoutchouc is 
white, and may be obtained in this state by dissolving in washed ether 
and precipitating it by the addition of alcohol, in which it is insoluble. 
The caoutchouc of commerce contains a small quantity of albumen, derived 
from the original milky liquid, this being really a solution of albumen 
holding in suspension about 30 per cent, of caoutchouc, which rises to the 
surface like cream, when the juice is diluted with water and allowed to 
stand, becoming coherent and elastic when exposed to air. It will be 
remembered that many of the chief uses of caoutchouc depend upon its 
physical rather than its chemical properties, its lightness (sp. gr. 0*93) 
and impermeability to water, adapting it for the fabrication of waterproof 
articles of clothing, of life-buoys, &c, while its remarkable elasticity gives 
rise to a still greater variety of applications. 

For the manufacture of waterproof cloth, caoutchouc is dissolved in 
rectified turpentine, and the solution is spread, in a viscid state, over the 
surfaces of two pieces of cloth of the same size, which are then laid face 
to face and passed between rollers, the pressure of which causes perfect 



488 INJDIA-RUBBER. 

adhesion between the two surfaces. Carbon disulphide, benzene, and cdal 
naphtha, petroleum, the oils, both fixed and volatile, are also capable of 
dissolving caoutchouc. 

Marine glue is a solution of caoutchouc with a little shell-lac in coal-tar 
naphtha. 

Waterproof felt is made by matting together fibres of cotton im- 
pregnated with a solution of caoutchouc in naphtha, and passing the felt 
between rollers. "When kept for a length of time its strength and water- 
proof qualities are deteriorated, in consequence of the oxidation of the 
caoutchouc, which is thus converted into a resinous substance resembling 
shell-lac, and easily dissolved by alcohol. 

The alkalies and diluted acids are without effect upon caoutchouc. When 
gently warmed it becomes far more soft and pliable ; it fuses at about 
250° F., and is converted into an oily liquid which becomes viscid on 
cooling, but will not again solidify, and is useful for lubricating stop- 
cocks. When further heated in air it burns with a bright smoky flame. 
Heated in a retort, caoutchouc is decomposed into several hydrocarbons, 
one of which, called isoprene, boils at about 100° F., and has the com- 
position C 5 H 8 , while caoutchine has the same composition as oil of 
turpentine, and boils at 340° F. ; they are well adapted for dissolving- 
caoutchouc. 

Vulcanisd caoutchouc is produced by incorporating this substance 
w r ith 2 or 3 per cent, of sulphur, which not only increases in a remark- 
able manner its elasticity, but prevents it from cohering under pressure, 
and from adhering to other surfaces unless strongly heated. The 
vulcanised caoutchouc is also insoluble in turpentine and naphtha. 
Ordinary vulcanised caoutchouc generally contains more sulphur than is 
stated above, which causes it to become inelastic and brittle after it has 
been sometime in use ; and for some purposes, such as the manufacture 
of overshoes, it is found advantageous to add some lead carbonate as well 
as sulphur. 

When a sheet of caoutchouc is allowed to remain for some time in 
fused sulphur at 250° F., it absorbs 12 or 15 per cent, of that element 
without suffering any material alteration ; but if it be heated for a short 
time to 300° F., it becomes vulcanised; and when still further heated, is 
converted into the black horny substance called vulcanite or ebonite, and 
used for the manufacture of combs, &c. By treating the vulcanised 
caoutchouc with sodium sulphite, the excess of sulphur above 2 or 3 per cent, 
may be dissolved out. The whole of the sulphur may be removed, and 
the caoutchouc devulcanised, by boiling it with a 10 per cent, solution of 
caustic soda. 

There are several processes employed for the manufacture of vulcanised 
caoutchouc j sometimes the sulphur is simply incorporated with it by 
mechanical means. Another process consists in immersing the caoutchouc 
in a mixture of 100 parts of carbon disulphide, and 2*5 parts of chloride of 
sulphur (S 2 C1 2 ),* or in dissolving the sulphur in oil of turpentine, which 
is afterwards used to dissolve the caoutchouc; when the turpentine has 
evaporated, a mixture of caoutchouc and sulphur is left, which may easily 
be moulded into any desired form, and afterwards vulcanised by exposure 
to high pressure steam having a temperature of about 280° F. 

The true chemical constitution of vulcanised caoutchouc is not yet 
* A mixture of sulphur and chloride of lime is said to be sometimes employed. 



GUTTA PERCHA — CORK. 489 

understood: it has been suggested that the sulphur has been substituted 
for a portion of the hydrogen in the original caoutchouc, but it does not 
seem improbable that this hydrocarbon may combine directly with sulphur. 

Caoutchouc is by no means rare in the vegetable world, being found in 
the milky juices of the poppy (and thence in opium), of the lettuce, and 
of the euphorbium and asclepia families. 

Gutta percha, like caoutchouc, is originally a milky juice, which exudes 
from incisions made into the wood of the Isona.ndra percha, a native of 
the Eastern archipelago. This juice soon solidifies, when exposed to air, 
to a brownish mass heavier than caoutchouc (sp. gr. 0*98), and differing 
widely from it by being tough and inelastic at the ordinary temperature, 
becoming quite soft and plastic when heated nearly to the boiling-point 
of water. Being impervious to water, it is employed as a waterproof 
material and for water-pipes, whilst its want of conducting power for 
electricity is turned to account in the coating of wires for the electric 
telegraph. 

Gutta percha is dissolved by the same substances which dissolve 
caoutchouc. It dissolves very slowly in ether, but is not affected by 
diluted acids and alkalies, and is employed for the manufacture of bottles 
in which hydrofluoric acid is kept. It liquefies at a moderately high 
temperature, and is afterwards decomposed, yielding products similar to 
those obtained from caoutchouc. 

The gutta percha of commerce appears to contain only about 80 per 
cent, of pure gutta percha (C 20 H 32 ), which is soluble in ether, the re- 
mainder consisting of two resins, which may be dissolved out by boiling 
with alcohol, when a white crystalline resin (C 20 H 32 O 2 ) is deposited on 
cooling, leaving an amorphous resin (C 20 H 32 O)-in solution. 

Pure gutta percha, exposed to air, is gradually converted into these 
resinous bodies, unless light be excluded. 

Cork is the bark of a species of oak (Quercus suber) growing chiefly in 
France and Spain. It consists chiefly of a cellular substance, insoluble 
in water, alcohol, and ether, termed suberine, which is richer in carbon than 
cellulose, and yields suberic acid when oxidised by nitric acid. It is much 
lighter than cellulose (sp. gr. 1 4). The waterproof nature of cork is 
due to the presence of eerine, which forms about 2 or 3 per cent, of the 
cork, and may be extracted from it by boiling with alcohol ; it is de- 
posited in needles on cooling. 

346. Gums. — Connected with the substances just described as being 
immediate products of Vegetable life, are the gums, which, though resem- 
bling the resins in transparency and lustre, are at once distinguished from 
them by their solubility or softening in water,, and by their insolubility in 
alcohol. 

Gum arable, which may be studied as the representative of this class, 
is an exudation from certain species of acacia, and consists essentially of 
arabine, which has the composition C 12 H 22 O n . It dissolves readily, even 
in cold water, in large proportion, forming a viscid liquid, from which the 
arabine is precipitated in white flakes on adding alcohol. 

When arabine is boiled with diluted sulphuric acid, it is slowly converted 
into grape-sugar (C 6 H 14 7 ) by assimilating the elements of water, a pro- 
perty connecting it closely with starch, which is susceptible of a simiiar 
conversion. 



490 GUM — STARCH. 

But a chemical property distinguishing the gums is their behaviour 
with nitric acid, which furnishes mucic acid (H 2 C 6 H 8 8 ) and oxalic acid 
(H 2 C 2 4 ). The latter acid is also formed by the action of nitric acid upon 
starch and sugar, whilst mucic acid may be obtained by a similar process 
from sugar of milk and from manna sugar (mannite). 

Gum Senegal is often used in place of gum arabic, especially by calico- 
printers to thicken their colours. It is darker in colour than gum arabic, 
but also consists essentially of arabine. 

Gum tragacanth (O 12 H 20 O 10 ), which exudes from the Astragalus traga- 
cantha, is far less transparent than gum arabic, from which it also differs 
by not dissolving in water, but merely swelling up to a soft gelatinous 
mass. This variety of gum, which is also called mucilage, cerasine, or 
bassorhie, is found, together with arabine, in the gum which exudes 
from the cherry, plum, almond, and apricot trees, and gives the mucila- 
ginous character to the watery decoctions prepared from certain seeds, such 
as linseed and quince-seed, and from the root of the marsh-mallow. 

Gelose or China-moss resembles the gums, and is remarkable for forming 
a jelly with 500 parts of water. Its formula is said to be C 6 H 10 O 5 . 

Starch. 

347. Starch (CgH^Og) differs widely from the vegetable products just 
noticed, in being an indispensable constituent of certain parts of plants, 
in possessing an organised structure, and playing a very important part in 
the nutrition of the plant. 

In composition, it is seen to correspond with cellulose, which has also, 
it will be remembered, an organised structure ; but the function of cellu- 
lose in the plant appears to be chiefly, if not entirely, a mechanical one, 
since it forms the skeleton or framework of the plant, for which its resist- 
ance to chemical change especially adapts it ; whilst it will be seen that 
starch suffers chemical changes in the vegetable, which may be compared 
in some measure to the digestion of the food in the animal body. 

Starch is manufactured chiefly from potatoes, wheat, and rice, the solid 
portion of which consists chiefly of starch, as appears in the following 
result of analysis : — 





Potatoes. 


Wheat. 


Eice. 


Starch, 


. 20-2 


60-8 


83-0 


Water, 


. 75-9 


121 


5-0 


Gluten, 




10-5 


6-0 


Albumen, 


'.. 2 : 3 


2-0 




Dextrine and sugar, 




10-5 


i v o 


Woody fibre, 


'. : 4 


1-5 


4-8 


Oily matter, 


. 0-2 


11 


01 


Mineral matter, 


1-0 


15 


o-i 



100-0 100-0 100-0 

In order to extract the starch, the potatoes are rasped to a pulp, which 
is washed upon a sieve, under a stream of water, as long as the latter is 
rendered milky by the starch suspended in it, the woody fibre being left 
behind upon the sieve. The milky liquid is allowed to settle, and the 
clear water drawn off; the deposited starch is then stirred up with fresh 
w r ater, and again allowed to subside, this process being repeated as long 
as the water is coloured, after which the starch is mixed up with a small 
quantity of water, and passed through a fine sieve to separate mechani- 



MANUFACTURE OF STARCH. 



491 



cally mixed impurities ; it is finally drained and dried, first in a current 
of air, and afterwards by a gentle heat. 

Starch cannot be extracted from wheat so easily as from potatoes, on 
account of the much larger proportion of other solid matters from which 
it must be separated. 

To extract the starch, the coarsely-ground wheat is moistened with 
water, and allowed to putrefy, as it easily does, in consequence of the alter- 
able character of the gluten (which contains carbon, hydrogen, nitrogen, 
oxygen, and sulphur) • the putrefying gluten excites fermentation in the 
sugar and part of the starch, producing acetic and lactic acids. These 
acids are capable of dissolving the remainder of the gluten, which may 
then be washed away by water, the subsequent processes being similar to 
those employed in the extraction of potato starch. 

A far more economical and scientific method of extracting the starch 
consists in dissolving the gluten by means of a weak alkaline solution, 
which leaves the starch untouched. This process is especially applied in 
the manufacture of starch from rice. 

The whole rice is allowed to soak for twenty-four hours in water con- 
taining -g-4-Qth of its weight of caustic soda ; it is then washed and ground 
into flour, which is again soaked for two or three days in a fresh alkaline 
solution ; the starch is allowed to settle, and the alkaline liquor holding 
the gluten in solution is drawn off. To complete the purification of the 
starch, it is stirred up with water, the heavier woody fibre allowed to sub- 
side, and the milky liquid is run off into another vessel, where it deposits 
the starch. 

Starch is usually sent into commerce in the rough prismatic fragments 
into which it splits during the process of drying, and is generally coloured 
blue by the addition of a little artificial ultramarine or smalt, in order to 
correct the yellow tint of linen. Commercial starch generally contains 
about 18 per cent, of water. 

Starch being possessed of an organised structure, might be expected to 
vary in external characters with the source from which it was derived ; 
and, accordingly, we find that, with the help of the microscope, it may be 
ascertained from what plant any particular specimen of starch was pro- 
cured, a result which could not be arrived at by a chemical examination. 

Thus, powdered starch from the potato (P, fig. 285) appears under the 
microscope in very irregular ovoid granules, marked with concentric rings, 




Fig. 285. 



and of larger size than those from most other vegetables, the long diameter 
of the grains being usually about g-J-g- inch. Wheat starch (W) exhibits 
grains which are nearly circular, and are not marked with rings ; they are 
much smaller than those of potato starch, having a diameter of about 
ToVo °f aa i nca - The grains of rice starch (R) are angular, and still 



492 PROPERTIES OF STARCH. 

smaller, measuring only about goVo °^ an ^ ncn i a diameter. A represents 
the starch granules of arrow-root. 

Starch is quite unaffected by cold water ; but if it be heated with water 
to a temperature above 140° F., the granules swell up, burst, and yield 
the well-known viscid liquid used by laundresses. If this be mixed with 
a large quantity of water, and allowed to stand, some of the imperfectly 
burst granules subside, but the greater part of the starch remains so inti- 
mately mixed with the water, that it is not separated by filtration through 
paper, though it has been shown that when the rootlets of a hyacinth are 
immersed in the diluted magma of starch, the water alone is taken up by 
the capillary vessels, affording a strong presumption that the starch was 
simply in a state of suspension in the water. If the boiled starch be eva- 
porated to dryness, a brittle mass remains, which may again be taken up 
without difficulty by water. 

This peculiar behaviour of starch with water is closely connected with 
its use as food. Raw starch is digested with difficulty, and often passes 
unaltered through the bowels ; but the ease with which the starch gela- 
tinised by heat is digested, is shown by the wholesomeness of sago, 
tapioca, and arrow-root, which consist simply of starch, and are prepared 
for food by heating them with water to the point at which the granules 
burst. 

Arrow-root is the starch extracted from the root of the Maranta arun- 
dinacea, and of some other tropical plants. 

In the preparation of tapioca and sago, the starch is dried at a tem- 
perature above 140° F., so that it loses its ordinary farinaceous appearance 
and becomes semi-transparent. 

Sago is manufactured from the pith of certain species of palm, natives 
of the East Indian islands. The tree is split so as to expose the pitb, 
which is mixed with water, and the starch having been separated from 
the woody fibre in the usual manner, is pressed- through a perforated 
metallic plate, which moulds it into small cylinders ; these are placed in a 
revolving vessel and broken into rough spherical grains, which are steamed 
upon a sieve, and dried. 

Tapioca is obtained from the roots of the Jatropha manihot, a native 
of America. The roots are peeled and subjected to pressure, which 
squeezes out a juice employed by the Indians to poison their arrows, and 
containing a deleterious substance which has been named jatrophine. 
"When the juice is allowed to stand, it deposits starch, which is well 
washed, pressed through a colander, and dried at 212° F. 

Oswego, or corn-flour, is the flour of Indian corn deprived of gluten by 
treatment with a weak solution of soda. 

348. Dextrine, — TThen starch is heated in an oven to about 400° F. 
for an hour or two, it becomes easily soluble in cold water, yielding a 
solution having all the properties of gum ; the starch has indeed been 
converted into a new substance known as dextrine or British gum, which 
is largely used by calico-printers for thickening their colours, and is sub- 
stituted for ordinary gum in many other applications. There is a current 
anecdote which attributes tht discovery of dextrine to a conflagration at 
a starch -factory, where the work-people, who assisted in quenching the 
fire, observed the gummy properties of the water which had been thrown 
over the torrefied starch. In toasting bread, a portion of the starch is 



CONVERSION OF STARCH INTO DEXTRINE. 493 

converted into dextrine, which is dissolved by the water in the prepara- 
tion of toast and water. Farinaceous foods for infants are made by baking 
flour, in order to convert the starch into dextrine. 

It is very remarkable that the composition of dextrine (C 6 H 10 O 5 ) is 
precisely that of starch ; they are isomeric bodies, so that the difference in 
their properties must be ascribed to a difference in the arrangement of 
their component particles; the name of dextrine was conferred upon this 
gummy substance on account of the power possessed by its solution of 
causing a right-handed rotation in a ray of polarised light. When oxidised 
by nitric acid, dextrine, like starch, is converted into oxalic acid, a cir- 
cumstance distinguishing it from the ordinary gum, which furnishes mucic 
acid when acted upon by nitric acid. 

Dextrine is usually prepared on the large scale by moistening 10 parts 
of starch with 3 parts of water acidulated with T i-oth of nitric acid ; the 
mixture is allowed to dry, and spread upon trays in an oven, where it is 
heated for an hour or so to 240° F. The nitric acid thus allows the 
starch to be converted into dextrine at a temperature which would be 
quite inadequate to effect the transformation of starch alone. 

This power of accelerating the conversion of starch into dextrine is 
shared by all acids. Hence if starch be boiled with water, and the viscid 
liquid so obtained be mixed with an acid, and again boiled, it gradually 
becomes thinner, and is eventually converted into dextrine. The change 
is very readily effected by boiling the starch solution with a few drops of 
sulphuric acid, and the gradual conversion of the starch may be traced by 
means of an aqueous solution of iodine. On adding this solution to a 
portion of the (cold) solution of starch, it produces the usual dark blue 
colour ; but on adding it, at intervals, to portions of the acidulated and 
boiled liquid, taken away and cooled for the purpose, the blue colour will 
be replaced by a peculiar vinous purple tint which iodine imparts to solu- 
tions of dextrine containing a little unchanged starch. 

The solution of iodine is much used in proximate organic analysis as a 
test for starch, and it is necessary to bear in mind that the blue colour is 
bleached by alkalies (which take up the iodine) and by heat, though, in 
the latter case, it may be restored by cooling the liquid. The blue colour 
does not appear to be due to the formation of any definite chemical com- 
pound with the starch, but rather to a mechanical adhesion of very finely 
divided iodine to the particles of starch. The sensitiveness of starch to 
the action oifree. iodine has given rise to its application in the preparation 
of paper for the prevention of forgery in bankers' cheques, &c. If paper 
be impregnated with a mixture of potassium iodide and starch, which 
is perfectly white, it will acquire an intense blue colour on the application 
of any of the bleaching agents (chlorine, hypochlorous acid, chlorides of 
lime and soda) generally used for removing ink, as these liberate the 
iodine, which immediately blues the starch. 

If the ebullition of the dextrine in contact with the sulphuric acid be 
continued, the solution entirely loses its property of being coloured by 
iodine, and acquires a sweet taste, the dextrine having been converted 
into glucose (C 6 H 12 6 ) by assimilating the elements of a molecule of 
water; * C 6 H 10 O 5 {Dextrine) + H 2 = C 8 H 12 6 (Glucose). 

* There is some reason to believe that the formation of glucose from starch results from 
a change similar to that by which it is obtained from salicine and other glucosides. Thus 
2C 6 H 10 O 5 + H 2 = C 6 H l0 O 5 + C fi H 12 6 
Dextrine. Glucose. 



494 GERMINATION OF SEEDS. 

349. Germination of seeds — Malting. — This tendency of starch to com- 
bine with the elements of water and pass into glucose, will be found of 
immense importance in the chemistry of vegetation, as well as in that of 
food. It is, indeed, the chief chemical change concerned in the develop- 
ment of living from inanimate matter, being one of the first processes 
involved in the germination of a seed — the first step in the production of 
vegetables, which must precede the animals whose food they compose. 

The components of all seeds are similar to those of wheat, which have 
been enumerated above ; and if they be perfectly dried immediately after 
their removal from the parent plant, they may be preserved for a great 
length of time unchanged, and without losing the power of germinating 
under favourable circumstances. The essential conditions of germination 
are the presence of air and moisture, and a certain temperature, which varies 
with the nature of the seed. These conditions being fulfilled, the seed 
absorbs oxygen from the air, and evolves carbonic acid gas, produced by the 
combination of the oxygen with the carbon of one or more of the most alter- 
able constituents of the seed, such as the vegetable albumen or the gluten. 
This process of oxidation is attended with evolution of heat, which serves 
to maintain the seed at the degree of warmth most favourable to germina- 
tion. The component particles of the albumen or gluten having been set 
in motion by the action of the atmospheric oxygen, induce a movement 
or chemical change in the starch with which they are in contact, causing 
it to pass into dextrine and glucose, which, unlike the starch, being 
perfectly soluble in water, are capable of affording to the developing shoot 
the carbon, hydrogen, and oxygen which it requires for the increase of its 
frame. The production of glucose and of dextrine in germination is 
well illustrated by the sweet gummy character of the bread made from 
sprouted wheat, and is turned to practical account in the process of 
malting. 

During the germination of all seeds there is formed, apparently by the 
oxidation of one of the more alterable constituents, a peculiar substance 
containing carbon, hydrogen, nitrogen, and oxygen, which has never yet 
been obtained from any other source, and is characterised by its remark- 
able property of inducing the conversion of starch into dextrine and grape- 
sugar. 

This substance has been termed diastase (Siao-rao-is, dissension; metaph. 
fermentation), but has never yet been obtained in a state of sufficient 
purity to enable its formula to be satisfactorily determined. It may be 
extracted, however, from malt, by grinding it and mixing it with half 
its weight of warm water, which dissolves the diastase ; the solution 
squeezed out of the malt is heated to about 170° F.,' filtered from any 
coagulated albumen, and mixed with absolute alcohol, which precipitates 
the diastase in white flakes. One part of diastase dissolved in water is 
capable of inducing the conversion of 2000 parts of starch into dextrine 
and grape-sugar, the diastase itself being exhausted in the process. A 
temperature of about 150° F. is most favourable to the action of diastase, 
which may be arrested entirely by raising the liquid to the boiling- 
point. 

The great importance of diastase in the arts of the brewer and distiller 
is at once apparent. In the process of malting barley, the grain is soaked 
in water, and afterwards spread out in thin layers upon the floor of a dark 
room (thus imitating the natural condition under which the seed germi- 



PROCESS OF MALTING. 



495 



nates), which is maintained as nearly as possible at a constant and moderate 
temperature (between 55° and 62° F.) ; spring and autumn are, therefore, 
more favourable to malting than summer and winter. It soon evolves 
heat, and the grains begin to swell; in the course of twenty-four hours 
the germination commences, and the radicle makes its first appearance as 
a whitish protuberance ; the grain is turned two or three times a day, in 
order to equalise the temperature. In about a fortnight the radicle has 
grown to about half an inch, by which time a sufficient quautity of dias- 
tase has been formed. In order to prevent the germination from proceed- 
ing further, the grain is killed by drying it at a temperature of 90° F. on 
perforated metallic plates, where it is afterwards heated to about 140° F., 
so as to render it brittle, after which it is sifted in order to separate the 
radicle, which is now easily broken off. This radicle is found to contain 
as much as ^th of the total quantity of the nitrogen present in the barley, 
so that the malt dust, as the siftings are called, forms a valuable 
manure. 

One hundred parts of barley generally yield about 80 parts of malt, but 
a part of the loss is due to water present in the barley, so that 100 parts of 
dry barley yield 90 parts of malt and 4 parts of malt dust, the difference, 
viz., 6 parts, representing the weight of the carbon converted into carbonic 
acid gas, of the hydrogen (if any) converted into water during the germina- 
tion, and of soluble matters removed from the barley in steeping. Malt 
contains about T Jq^ 1 °^ ^ s weight of diastase, far more than enough to 
ensure the conversion of the whole of its starch into sugar. 

The following table* illustrates the change in composition suffered by barley 
during the process of malting, leaving the moisture out of consideration : — 



Sugar, 

Starch, . . . 1 
Dextrine, . . ( 
Woody fibre, . 
Albuminous matter, 
Mineral matter, 


Barley. 


After 
Steeping. 


14£ d-ays on 
floor. 


Malt after 
Sifting. 


Malt Dust. 


2-56 

80-42 

4-69 
9-83 
2-50 


1-56 

81-12 

5-22 
9-83 
2-27 


1214 

70-09 

5-03 

10-39 

2-35 


11-01 

72-03 

4-84 
9-95 
2-17 


11-35 

43-68 

9-67 

26-90 

8-40 




100-00 100-00 


100-00 


100-00 


100-00 



350. Breioing. — In order to prepare beer, the brewer maslies the ground 
malt with water at about 180° F., for some hours, when the diastase 
induces the conversion, into dextrine and sugar, of the greatest part of the 
starch which has not been so changed during the germination, and the 
wort is ready to be drawn off for conversion into beer. The undissolved 
portion of the malt, or brewers' grains, still contains a considerable quantity 
of starch and nitrogenised matter, and is employed for feeding pigs. 

That malt contains far more diastase than is necessary to convert its 
starch into sugar, is shown by adding a little infusion of malt to the 
viscid solution of starch, and maintaining it at about 150° F. for a few 
hours, when the mixture will have become far more fluid, and will no 
longer be coloured blue by solution of iodine. In distilleries, advantage 
is taken of the excess of diastase in malt, by adding three or four parts of 
unmalted grain to it, when the whole of the starch in this latter is also 

* Lawes, Report of the Relative Values of Unmalted and Malted Barley as Food for 
Stock, 1866. 



496 CHEMISTRY OF BREWING. 

converted into dextrine and sugar, and the labour and expense of malting 
it are avoided. 

The wort obtained by infusing malt in water contains not only glucose, 
dextrine, and diastase, but a considerable quantity of nitrogenised matter 
formed from the gluten (or albuminous matter) of the barley. Before 
subjecting it to fermentation, it is boiled with a quantity of hops, usually 
amounting to about ^th of the weight of the malt employed, which is 
found to prevent, in great measure, the tendency of the beer to become 
sour in consequence of the conversion of the alcohol into acetic acid. 

The hop contains about 10 per cent, of an aromatic yellow powder, 
called lupuline, which appears to be the active portion, and which con- 
tains a volatile oil of peculiar odour, together with a very bitter substance. 
The hopped wort is run off into a vat, where it is allowed to deposit 
the undissolved portion of the hops, and the clear liquor is drawn off 
into shallow coolers, where its temperature is lowered as rapidly as pos- 
sible to about 60° F., the cooling being usually hastened by cold water 
circulating through pipes which traverse the coolers. If the wort be 
cooled too slowly, the nitrogenised matter which it contains undergoes 
an alteration by the action of the air, in consequence of which the beer 
is very liable to become acid. 

The wort is now transferred to the fermenting tun, where it is made 
to ferment by the addition of yeast, usually in the proportion of T ^o^ 
of its volume. 

Yeast is a minute fungoid vegetable, which grows in solutions con- 
taining sugar together with some nitrogenised substance (e.g., a salt of 
ammonium), and the salts (phosphates of potassium, sodium, calcium, and 
magnesium), which are essential constituents of its cells. If a little white 
of egg, cheese, or a piece of flesh (all of which contain carbon, hydrogen, 
nitrogen, oxygen, and phosphates), be placed in a solution of sugar, and 
allowed to undergo decomposition, a grey scum forms upon the liquid, 
which is seen under the microscope to consist of irregularly oval cells, 
the growth of which may be watched under the microscope in a little of 

the liquid from which they were obtained, 
when they will be found to multiply rapidly 
by the production of new cells on all sides of 
them (fig. 286). The same cells will be 
developed very rapidly in the sweet wort of 
malt, allowed to undergo decomposition be- 
tween 60° and 70° F. 

These cells contain a substance somewhat 
resembling albumen, enclosed in a thin mem- 
brane, the composition of which is similar to 
that of cellulose. They also contain a peculiar 
nitrogenised body resembling diastase, and 
capable of inducing the conversion of cane- 
Fig. 286. sugar (C 12 H 22 O n ) into glucose (C 6 H 12 O ). 
Accordingly, when yeast is added to a solution 
of cane-sugar, the liquid is found to increase in specific gravity (a solution 
of cane-sugar having a lower density than one containing an equivalent 
quantity of glucose), previously to the commencement of fermentation, 
and the application of tests readily proves the presence of glucose in the 
solution. 




FERMENTATION. 497 

The glucose then undergoes the decomposition known as alcoholic 
fermentation, which results in the production of alcohol, carbonic acid, 
lactic acid, succinic acid, glycerine, and a peculiar brown soluble matter, 
together with other substances, the true nature of which is yet undeter- 
mined. The fermentation is attended with a considerable elevation of 
temperature. 

Taking into consideration only the alcohol and carbonic acid gas, which 
are the chief products, their formation from grape-sugar may be repre- 
sented by the equation C 6 H 12 6 = 2C 2 H 6 + 2C0 2 . 

During the fermentation the yeast cells are gradually broken up, so 
that a given quantity of yeast is capable of fermenting only a limited 
quantity of sugar. On an average, a quantity of yeast containing between 
two and three parts of solid matter is required to complete the fermenta- 
tion of 100 parts of sugar. The solution remaining after the fermenta- 
tion is found to contain salts of ammonium, which have been formed at 
the expense of the nitrogen of the yeast. 

If the liquid in which the yeast excites fermentation contains nitro- 
genised matters and phosphates, the yeast-plant grows, and its quantity 
increases; thus, in the sweet wort from malt, the yeast is nourished by 
the altered gluten and by the phosphates, so that it increases to six 
or eight times its original weight. 

If yeast be heated to the boiling-point of water, the plant is killed, 
as might be expected, and loses its power of inducing alcoholic fermenta- 
tion; but it may be dried at a low temperature, or by pressure, without 
losing its fermenting power, and dried yeast is an article of commerce. 
German dried yeast is produced in the fermentation of rye for making 
Hollands. 

Yeast will not cause fermentation in a solution containing more than 
one-fourth of its weight of sugar, and the fermentation is arrested when 
the alcohol amounts to one-fifth of the weight of the liquid, so that the 
strength of fermented liquors could never exceed 20 per cent, of alcohol. 
The fermentation is also arrested by the mineral acids, and by many of 
the substances to which antiseptic properties are commonly attributed, 
such as common salt, kreasote, corrosive sublimate, sulphurous acid, tur- 
pentine, &c. 

In the fermentation of beer, the yeast is carried up to the surface by 
the effervescence due to the escape of the carbonic acid gas, and is 
eventually removed, in order to be employed for the fermentation of fresh 
quantities of wort. When the fermentation has proceeded to the required 
extent, the beer is stored for com sumption. 

It will be seen that the chief constituents of beer are the alcohol, 
the nitrogenised substance derived from the albuminous matter of 
the barley, and not consumed in the growth of the yeast, the unaltered 
glucose and dextrine, the brown or yellow colouring matter formed 
during the fermentation, the essential oil and bitter principle of the 
hop. 

Beer also contains acetic acid (formed by the oxidation of the alcohol, 
page 498), free carbonic acid, which gives its sparkling character, together 
with the lactic and succinic acids and gtycerine, formed as secondary pro- 
ducts of the fermentation, and ammoniacal salts derived from the yeast. 
The soluble mineral substances from the barley are also present, minus 
the phosphates abstracted by the yeast. 

2i 



498 



COMPOSITION OF BEER. 



The proportions of the constituents, of course, vary greatly, as will be 
seen from the following examples : — 



Percentage. 


Allsopp's 
Ale. 


Bass's Ale. 


Strong Ale. 


Whitbiead's 
Porter. 


Whitbiead's | 
Stout. | 


Alcohol, . 
Acetic acid, 
Sugar and other solid ) 
matters, . . \ 


6-00 
0-20 

5-00 


7-00 
0-18 

4-80 


8-65 
0-12 

6-60 


4-20 
0-19 

5-40 


6-00 
018 

6-38 



The dark colour of porter and stout is caused by the addition of a 
quantity of high-dried malt which has been exposed to so high a tempera- 
ture in the kiln as to convert a portion of its sugar into a dark brown 
soluble substance called caramel. The peculiar aroma of beer is probably 
due to the presence of acetic ether, produced during the fermentation. 

In some cases, when the operation of brewing has been badly con- 
ducted, the beer becomes ropy, or undergoes the viscous fermentation. In 
this case the glucose suffers a peculiar transformation, resulting in the pro- 
duction of a mucilaginous substance resembling gum ■ in its composition. 
This change may be induced by yeast which has been boiled, or by water 
in which flour or rice has been steeped. White wine occasionally 
becomes ropy from a similar cause, but red wines are not liable to this 
change, apparently because the tannin which they contain has precipitated 
in an insoluble form the ferment which induces it. During this viscous 
fermentation a part of the glucose is often converted into mannite 
(C„H 14 6 ). 

351. Acetification — Manufacture of Vinegar. — Beer which has 
become sour is often said to have undergone the acetous fermentation ; 
but this is not strictly correct, the change being more similar to decay, 
since it is one in which the oxygen of the air directly takes part. The 
acidity of sour beer is caused by the acetic acid (C 2 H 4 2 ) formed by the 
action of atmospheric oxygen upon the alcohol, according to the equation— 

C 2 H 6 (Alcohol) + 2 = C 2 H 4 2 (Acetic acid) + H 2 0. 

Pure alcohol may be exposed to the air, either alone or when mixed with 
water, for any period, without suffering oxidation; but when in contact 
with certain changeable organic substances, the alcohol undergoes oxida- 
tion, and is converted into acetic acid. It is upon this circumstance that 
the different methods of producing vinegar are based. 

The most direct application of this principle is made in the so-called 
quick vinegar process in use in continental countries where alcohol is 
free of duty. Alcohol of about 80 per cent, is mixed with 6 parts of 
water, and with about T oVo"th part of yeast, or some other alterable sub- 
stance containing nitrogen. This mixture is heated to about 80° F., and 
caused to trickle slowly from pieces of cord fixed in a perforated shelf over 
a quantity of wood shavings* previously soaked in vinegar, which is found 
materially to assist the acetification, and packed in a tall cask (fig. 287) 
in which holes have been drilled in order to allow the entrance of air. The 
oxidation of the alcohol soon raises the temperature to about 100° F., which 
occasions a free circulation of air among the shavings. The mixtureis 

* These shavings appear to favour the process by serving as points of attachment for a 
microscopic vegetable, which encourages the oxidation of the alcohol. 



MANUFACTURE OF VINEGAR. 



499 



passed three or four times through the cask, and in about thirty-six hours 
the conversion into vinegar is completed. The oxidation of the alcohol 
in this process is found to be arrested 
by the presence of essential oils, or of 
kreasote, and similar antiseptic sub- 
stances. 

The necessity of affording a full 
supply of atmospheric air was not 
appreciated until Liebig had proved 
the existence of an intermediate stage 
in the process, consisting in a partial 
oxidation of the alcohol by which 
it became converted into aldehyde 
(C 2 H 4 0), an extremely volatile liquid 
(boiling at 70° F.), which was lost 
in the form of vapour, thus greatly 
diminishing the proportion of vinegar 
obtained — 




287. 



C 2 H 6 (Ahohol) + 



C 2 H 4 (Aldehyde) + H 2 . 



If a sufficient quantity of atmospheric air be supplied, the production of 
aldehyde is entirely avoided. 

White wine vinegar is prepared in France from light wines by a process 
of much longer duration. A little boiling vinegar is poured into a cask, 
partially open at the top, together with 4 or 5 gallons of white wine 
which has been allowed to trickle over wood shavings. In a few days, 
during which the temperature is maintained at about 80° F., a fresh quan- 
tity of wine is poured in, and in the course of a fortnight half the vinegar 
contained in the cask is drawn off, and replaced by a fresh portion of wine. 
In this way an occasional renewal of the air in the upper part of the cask 
is provided for. The acetification is found to proceed more rapidly in old 
casks than in new ones, which is attributed to the presence of a peculiar 
conferva deposited upon the sides of the former, and styled mother of 
vinegar. It is probably for a similar reason that the acetification is pro- 
moted by the addition of ready-made vinegar at the commencement of the 
process. 

In this country vinegar is chiefly prepared from malt, the infusion of 
which is allowed to undergo the alcoholic and acetous fermentation. 

Vinegar contains on an average about 5 per cent, of acetic acid, together 
with small quantities of vegetable and mineral substances, varying with 
the source from which it was obtained. Its pleasant aroma is due to 
the presence of some acetic ether (C 2 H 5 .C 2 H 3 2 ) formed during its manu- 
facture. The vinegar of commerce is allowed to be mixed with T ^o~o^ n 
of its weight of sulphuric acid in order to prevent it from becoming 
mouldy. 



Bread. 



352. The chemistry of fermentation is intimately connected with the 
ordinary process of bread-making. It will be remembered that wheat en 
flour (page 490) consists, essentially, of starch and gluten, with a little 
dextrine and sugar. On mixing the flour with a little water, it yields a 
dough, the tenacity of which is due to the gluten present in the flour. If 



500 PROCESS OF BREAD-MAKING. 

this dough, be tied up in a piece of fine muslin, and kneaded under a stream 
of water, the starch will be suspended in the water, and will pass through 
the muslin, whilst the gluten will remain as a very tough elastic mass, 
which speedily putrefies if exposed to the air in a moist state, and dries 
up to a brittle horny mass at the temperature of boiling water. 

On analysis, gluten is found to contain carbon, hydrogen, nitrogen, and 
oxygen, in proportions which may be represented by the empirical formula 
C 24 H 40 X 6 O r , though it cannot be regarded as a single independent sub- 
stance, but as a mixture of three substances very closely allied in compo- 
sition. 

When gluten is boiled with alcohol, one portion refuses to dissolve, and 
has been named vegetable fibrine, from its resemblance to the substance 
forming the muscles of animals. When the solution in alcohol is allowed 
to cool, it deposits a white flocculent matter, very similar to the caseine 
which composes the curd of milk. On adding water to the cold alcoholic 
solution, a third substance (glutine) is separated, which much resembles 
the albumen found so abundantly in the blood. 

The presence in gluten of three substances, similar to the three principal 
components of the animal body, leads us to form a high opinion of its 
value as a nutritive compound. But gluten itself, separated from the flour 
by the process above described, would be found very difficult of digestion, 
on account of its resistance to the solvent action of the fluids in the 
stomach ; indeed, the dough composed of flour and water is proverbially 
indigestible, even when baked. In order to render it fit for food, it must 
be rendered spongy or porous, so as to expose a larger surface to the action 
of the digestive fluids of the body ; the most direct method of effecting 
this is the one adopted in the manufacture of the aerated bread, and con- 
sists in mixing the flour with water which has been highly charged, under 
pressure, with carbonic acid gas ; the mixing having been effected in a 
strong closed iron vessel, an aperture in the lower part of this is opened, 
when the pressure of the accumulated gas forces the dough out into the 
air, and the gas which had been imprisoned in the dough expands, con- 
ferring great porosity and sponginess upon the mass in its attempt to 
escape. In another process for preparing unfermented bread, the flour is 
mixed with a little bicarbonate of soda, and is then made into a dough 
with water acidulated with hydrochloric acid ; the latter decomposing 
the bicarbonate of soda, liberates carbonic acid gas, which renders the 
bread porous. The sodium chloride formed at the same time remains 
in the bread. In the preparation of cakes and pastry, the same object rs 
sometimes attained by adding carbonate of ammonia to the dough ; when 
heat is applied in the baking, the salt is converted into vapour which 
distends the dough. 

In the common process of bread-making, however, the carbonic acid gas 
destined to confer sponginess upon the dough is evolved by the fermenta- 
tion of the sugar contained in the flour ; the latter having been kneaded 
with the proper proportion (usually about half its weight) of water, a little 
yeast and salt are added, and the mixture is allowed to stand at a tempera- 
ture of about 70° F. for some hours. The dough swells or rises consider- 
ably in consequence of the escape of carbonic acid gas, the sugar being 
decomposed into that gas and alcohol, as in ordinary fermentation. The 
spongy dough is then baked in an oven, heated to about 500° F., when a 
portion of the water and the whole of the alcohol are expelled, the carbonic 



PRODUCTION OF GRAPE-SUGAR FROM STARCH. 501 

acid gas being also much expanded by the heat, and the porosity of the 
bread increased. The granules of starch are much altered by the heat, 
and become far more digestible. Although the temperature of the inside 
of the loaf does not exceed 212° F. the outer portion becomes torrefied or 
scorched into crust. 

Occasionally, instead of yeast, leaven is employed, in order to ferment 
the sugar, leaven being dough which has been left in a warm place until 
decomposition has commenced. 

The passage of new into stale bread does not depend, as was formerly 
supposed, upon the drying of the bread consequent upon its exposure to 
air, but is a true molecular transformation which takes place equally well 
in an air-tight vessel, and without any loss of weight. It is well known 
that when a thick slice of stale bread is toasted, which dries it still further, 
the crumb again becomes soft and spongy as in new bread; and if a stale 
loaf be again placed in the oven, it is entirely reconverted into new bread. 

Wheaten flour is particularly well fitted for the preparation of bread on 
account of the great tenacity of its gluten. Next to wheat in this respect 
stands rye, whilst the other cereals contain a gluten so deficient in tenacity 
that it is impossible to convert them into good bread. 

Barley bread is close and heavy, since its nitrogenised matter is chiefly 
present in the form of albumen, w r hich does not vesiculate like gluten, 
during the fermentation. 

Even in wheaten flour the tenacity of the gluten is liable to variation, 
and in order to obtain good bread from a flour the gluten of which is 
inferior in this respect, it is customary to employ a minute proportion of 
alum. This addition being considered unwholesome by some persons, it 
would be better to substitute lime-water, which, has been found by Liebig 
to have a similar effect. Sulphate of copper improves in a very striking 
manner the quality of the bread prepared from inferior flour, but this salt 
is far more objectionable than alum. 

The Sugars. 

353. The conversion of starch into grape-sugar, when heated in contact 
with diluted acids (page 493), is taken advantage of for the preparation of 
this variety of sugar on the large scale. For this purpose, water acidulated 
with Yxroth of sulphuric acid is heated to ebullition, and a hot mixture of 
starch and water allowed to flow gradually into it, so as not to reduce its 
temperature below the boiling-point. The mixture is kept boiling for 
half an hour, after which chalk is added in small portions at a time to 
neutralise the sulphuric acid, and the sulphate of lime having been allowed 
to subside, the clear syrup is drawn off, and evaporated to the crystallising 
point. The conversion is sometimes accelerated by heating under pressure 
with steam at 320° F. 

The grape-sugar or glucose thus manufactured cannot be employed as a 
substitute for the sugar extracted from the sugar-cane, on account of its 
greatly inferior sweetening power, which is less than half that possessed 
by cane-sugar.* It is, moreover, far less soluble in water, 1 part of grape- 
sugar requiring 1J part of water to dissolve it, whilst cane-sugar requires 
only J part. Grape-sugar has been employed, however, for the adultera- 

* Hence the loss of sugar by sweetening tarts before baking them, part of the sugar being 
converted into grape-sugar by the vegetable acids of the fruit. 



502 PRODUCTION OF SUGAR FROM CELLULOSE. 

tion of cane-sugar and honey. The fraud is easily detected in cane-sugar 
by boiling a portion of the sample with a little solution of potash, when 
the grape-sugar is decomposed, and colours the liquid intensely brown, 
pure cane-sugar giving very little brown colour unless boiled for a long 
time. A more delicate mode of detection consists in adding to a solution 
of the sugar a few drops of solution of cupric sulphate, and enough solu- 
tion of potash to form an intensely blue liquid. The cupric oxide is not 
precipitated in the presence of either of the sugars; but if the blue liquid 
be very gently heated, a red precipitate of cuprous oxide will separate if 
grape-sugar be present, whilst with pure, cane- sugar the precipitation does 
not take place unless the solution is boiled. Calcium sulphate will 
generally be detected in sugar or honey adulterated with glucose. 

Even cellulose is transformed into dextrine and glucose under the 
influence of sulphuric acid. If linen, calico, cotton- wool, or paper be dried 
and gradually moistened with 1J part of concentrated sulphuric acid, avoid- 
ing elevation of temperature, it is converted in the course of a few hours 
into a gummy mass which dissolves in water, and is very similar to dex- 
trine. When the cellulose has been left in contact with the acid for a day 
or two, it should be dissolved in a large quantity of water, and boiled for 
eight or ten hours hours in order to effect the conversion into glucose; the 
acid may then be neutralised with chalk, the solution filtered from the 
calcium sulphate, and evaporated, when it furnishes a crystalline mass of 
glucose. 

Closely connected with the conversion of cellulose into dextrine by con- 
tact with strong sulphuric acid, is that very remarkable change of paper 
into vegetable parchment. If dry white blotting-paper be drawn through 
a cooled mixture of the strongest oil of vitriol with half its bulk of water, 
and be then thoroughly washed in a large volume of water, it becomes 
five times as strong as before, and has f ths of the strength of ordinary 
animal parchment. The parchment paper, when dry, is found to have 
suffered no alteration in weight, and analysis shows its composition to be 
unchanged. This remarkable increase in strength must, therefore, be re- 
ferred to a molecular alteration. The paper is also found to have become 
almost waterproof, and presents a somewhat translucent appearance like 
paper which has been slightly oiled. It receives many useful applications, 
for lugggage labels which are not easily torn or removed by rain, and as a 
substitute for animal membrane in tying over preserves, &c. 

Hydrocellulose is the name given by A. Girard to the brittle substance into which 
cellulose is converted by the action of mineral acids on cellulose. It is prepared by 
immersing cellulose for twelve hours at 15° C. in sulphuric acid of sp. gr. 1 '453. It 
differs from cellulose in the facility with which it may be powdered, and in its greater 
susceptibility to oxidation and to the action of reagents. Its composition is represented 
by C 12 H 22 O n , which would be 2 molecules of cellulose, C 6 H 10 O 5 , with addition of the 
elements of water. Girard believes that the rotting of window curtains in towns is 
due to the conversion into hydrocellulose by the acid vapours in the air, and that dry 
rot in wood is due to a similar change caused by acid substances generated in the 
wood by fermentation. Hydrocellulose yields friable pyroxyline compounds when 
treated with the mixture of sulphuric and nitric acids. 

The susceptibility of conversion into grape-sugar possessed by starch and 
cellulose affords a very important clue in tracing the changes which take 
place in living vegetables. It has been already seen (page 494) that during 
the germination of seeds, their starch is converted into sugar, in order that 
it may be carried in a soluble form to the extending limbs of the vegetable 



EXTRACTION OF CANE-SUGAR. 503 

frame ; but it would appear that in these parts, where a deposition of 
cellulose is required, the sugar (C 6 H 12 6 ) is reconverted into that substance 
(C 6 H 10 O 5 ). In the ripening of the fruit, however, the ligneous matter and 
the starch seem to be again converted into sugar, under the influence of 
the vegetable acids which unripe fruits contain. 

The sugar contained in ripe fruits and in new honey is usually a mix- 
ture of about equal weights of grape-sugar or dextrose, and uncrystallisable 
sugar or levulose. These have the same composition (C 6 H 12 6 ), but levulose 
is more soluble in alcohol than dextrose, and rotates the plane in which a 
ray of light is polarised towards the left, while dextrose turns it towards 
the right hand. 

When starch is acted on by infusion of malt, it is converted into a 
particular kind of sugar termed maltose (C 12 H 22 O n .II 2 0), which is less 
soluble in alcohol than dextrose, into which it is converted by the action 
of acids. Its production seems to constitute an intermediate stage in the 
transition of starch, cellulose, and cane-sugar into grape-sugar. Hence it 
is found that if the ebullition with diluted sulphuric acid be arrested as 
soon as the liquid becomes sweet, no crystals can be obtained, but on 
further ebullition the levulose or fructose is converted into crystallisable 
glucose. When honey is kept for some time, the fructose gradually 
becomes converted into a crystalline mass of glucose. The same change 
is seen to take place in raisins, which contain granules of glucose, though 
the fresh grapes contain only fructose. Cold alcohol extracts about 35 
per cent, of levulose from honey, leaving about the same weight of 
dextrose which may be dissolved in boiling alcohol and crystallised. 
These crystals are anhydrous, but those obtained from an aqueous solution 
are C 6 H 12 6 .H 2 0. 

The uncrystallisable sugar forms the chief ingredient of molasses and 
treacle, for although the fresh juice of the sugar-cane contains no fructose, 
the treatment to which it is subjected in the extraction of the sugar 
occasions a copious formation of the uncrystallisable sugar at the expense 
of the cane-sugar. The simple ebullition of a solution of cane-sugar for a 
considerable period is said to convert a portion of it into fructose, and if 
a minute quantity of any uncombined acid be present, the change takes 
place very rapidily. Pure cane-sugar dissolved in water gradually changes 
into fructose when exposed to the light. 

354. Extraction of cane-sugar. — In the extraction of sugar from the 
sugar-cane, the latter is cut before the period of flowering, when, as might 
be expected, this soluble nutriment of the plant is most abundant. For 
a similar reason, the canes are cut off close to the ground, since in the 
higher joints of the cane much of the sugar has already been consumed for 
their development. A specimen of sugar-cane from Martinique was found 
to contain 90*1 per cent, of juice and 9 '9 of woody fibre, so that, theoreti- 
cally, 100 parts of cane should yield as much as 90 parts of juice. The 
canes are crushed between iron cylinders, which express, under the best 
arrangements, only 65 parts of juice from 100 of cane. It has been found 
possible to increase the yield by steaming the canes before submitting 
them to a final pressure. The juice thus expressed contains about 18 per 
cent, of sugar, together with the usual components of the sap of plants, 
such as vegetable acids, albumen, salts, &c. 

In the tropical climate in which the extraction is conducted, the albu- 



504 SUGAR-REFINING. 

men of the juice speedily alters when exposed to the air, and excites 
fermentation in the sugar, by which a considerable quantity would be lost. 
If the fresh juice were heated to coagulate the albumen, the free acid con- 
tained in it would change a portion of the sugar into the uncrystallisable 
variety. To avoid this, the juice is mixed with g^g-th part of slaked lime, 
and is then heated to 140° F. in large flat copper pans. The coagulated 
albumen rises to the surface of the heavy syrup, and forms a thick scum, 
which is taken off, and the clear syrup is evaporated till it is strong enough 
to crystallise, when it is run off into shallow wooden vats, and allowed 
to cool for twenty-four hours. When briskly stirred, it congeals to a 
semi-solid mass of crystals, which are allowed to drain for three weeks in 
casks with perforated bottoms. The raw sugar thus obtained, after dry- 
ing in the sun, is sent into commerce, the drainings being styled molasses 
or treacle. The weight of raw sugar seldom exceeds y^th of the juice, 
that is, about half the quantity which the juice is known to contain, the 
remainder having been converted into uncrystallised sugar during the 
process of extraction. The loss is found to be materially diminished by 
the use of vacuum pans, in which the evaporation of the syrup is con- 
ducted under diminished pressure, and therefore at a lower temperature. 
Greater economy is also introduced into the manufacture by the use of 
the crushed canes as fuel for the evaporating fires, and by restoring their 
ashes to the land as food for ensuing crops. The skimmings of the clarified 
juice are also advantageously used as manure. 

The raw sugar obtained by the process just described contains about 
60 per cent, of pure cane-sugar, the remainder consisting of water, un- 
crystallisable sugar, colouring matter, and various salts and other foreign 
substances derived from the cane-juice. 

In the ordinary process of sugar-refiyiing, two or three parts of raw 
sugar are dissolved in one part of water containing a little lime in solu- 
tion, and mixed with three or four parts of ground bone-black for every 
hundred of sugar ; a small quantity of serum of bullock's blood is also 
sometimes added. This mixture is heated by the passage of steam through 
it, when the albumen of the serum is coagulated, and rises to the surface 
in the form of a scum which entangles the floating impurities as well as 
the bone-black, and leaves the syrup much lighter in colour, a consider- 
able part of the colouring matter having been removed by the charcoal. 

The syrup is then filtered through a thick layer of coarsely powdered 
bone-black, and is thus rendered perfectly colourless and ready for evapora- 
tion, which is conducted in a boiler with double sides, so that it may be - 
heated by steam admitted between the two, and furnished with a dome 
from which the air may be exhausted in order to allow the evaporation 
to be conducted at a lower temperature, as well as out of contact with 
the atmospheric oxygen, so as to diminish as far as possible the produc- 
tion of uncrystallisable sugar. The boiling down of the syrup, which 
would require a temperature of 230° F. at the ordinary pressure, may 
thus be conducted at 160° F. When sufficiently evaporated,* the syrup 
is transferred to a heated vat, where it is stirred until a confused 
crystallisation commences, and is then drawn off into inverted sugar- 
loaf moulds of iron or earthenware, and allowed to crystallise during 

* The state of concentration of the syrup is known by the degree of viscidity which it 
exhibits between the ringer and thumb, by the length of the thread to which it may be 
drawn, and by the mode in which this curls after breaking. 



BEET-ROOT SUGAR. 505 

about twenty hours. The crystalline mass is then allowed to drain by the 
withdrawal of a plug at the apex of the inverted cone, and is washed 
with a little pure syrup to remove adhering colouring matter, after which 
the loaf is dried in an oven and finished by turning in a lathe. 

The operation of washing with syrup is often referred to as claying, 
being sometimes effected by placing some powdered sugar upon the base 
of each loaf, and over this a cream of pure pipeclay, the water draining 
from which dissolves the powdered sugar, and the syrup thus formed 
washes the loaf. The object of the clay appears to be simply to allow 
the water to flow gradually through the sugar. 

The process of refining is sometimes shortened by washing the raw 
sugar with strong syrup, so as to remove the bulk of the impurities at 
the commencement, and a very ingenious method, known as the centri- 
fugal process, has been devised for separating the syrup from the sugar 
thus washed. The pasty mixture of sugar and syrup is introduced into 
a cylinder of strong close metallic gauze, which is rapidly turned upon 
its axis, when the liquid syrup of course flies off through the apertures 
of the gauze, and is collected by a box surrounding the cylinder. A fresh 
quantity of syrup is then introduced, and separated in the same manner, 
so that the washing may be rapidly carried as far as may be deemed 
expedient. 

355. During the wars of Napoleon, when the importation of sugar into 
France was suspended, this substance was extracted from the beet-root, 
and this process still forms a very important branch of French industry. 

The white beet only is employed, on account of the difficulty of separ- 
ating the colouring matter existing in the juice of the red variety. The 
juice contains about 10 per cent, of cane-sugar, half of which only is 
usually obtained in the crystallised state. The process adopted for ex- 
tracting it does not differ in principle from that applied to the juice of 
the sugar-cane. 

Cane-sugar is also extracted in the United States from the sap of the 
sugar-maple, which is collected, usually in the spring, from deep incisions 
through the bark, into each of which a pipe of reed or elder is inserted 
to conduct the juice into pans placed for its reception, whence it is re- 
moved before it has had time to become changed by fermentation. The 
juice is evaporated rapidly, and the raw crystalline mass sold without 
further refining. On an average, each tree furnishes about 6 lbs. of sugar 
during the season. 

Sugar-candy consists simply of large rhomboidal prismatic crystals of 
sugar deposited upon strings stretched across crystallising troughs, in 
which a strong syrup is slowly evaporated at about 170° F. 

Barley-sugar is prepared by evaporating the syrup beyond the crystal- 
lising-point, till it solidifies, on cooling, to a vitreous mass, which is poured 
out on a cold surface and manipulated to the requisite forms. When 
kept for some time, the transparent barley-sugar becomes crystalline and 
opaque. 

Caramel (C 12 H 1S 9 ) is a dark brown substance produced by the action 
of a temperature of about 400° F. upon melted sugar. It is very soluble 
in water, and gives an intensely brown liquid, for which reason it is 
employed for colouring sauces, gravies, brandy, wines, &c. 

356. Chemical properties of the sugars. — Although cane- and grape-sugar appear to 
be essentially indifferent substances, they are remarkably prone to form combinations 



506 CHEMICAL PROPERTIES OF THE SUGARS. 

with many basic metallic oxides. Thus a solution of cane-sugar is capable of dissolv- 
ing a large quantity of lime, forming a compound (CaO.C^H^On) which is much 
more soluble in cold than in hot water, so that on boiling the transparent solution it 
becomes perfectly opaque, but resumes its transparency on cooling. This has been 
applied for separating the crystallisable sugar from molasses, the compound of sugar 
and lime, precipitated by boiling, being redissolved in cold water and treated with 
carbonic acid to separate the lime. 

On boiling lead hydrate with a solution of sugar, it is dissolved, and as the solution 
cools, a white powder is deposited, which has the composition 2PbO.C 12 H 18 9 .H 2 0, 
the water being expelled at a temperature of 212°. The composition of this compound 
would lead to the belief that cane-sugar contains two molecules of constitutional 
water, and that its formula should be written C 12 H 18 9 . 2H 2 0. By carefully heating 
cane-sugar, the compound C 12 H 20 O 10 , saccharide, has been obtained, and if this be 
further heated it yields C 12 H ]3 9 , caramel. When a solution containing 1 part of 
salt and 4 parts of sugar is allowed to evaporate spontaneously, it deposits a deli- 
quescent compound containing 2(NaCl.C 12 H 18 9 ).3H 2 0. 

Many metallic oxides form compounds with sugar, which are readily soluble in 
alkaline liquids, so that the addition of sugar to solutions of the oxides of copper and 
iron, for example, prevents the precipitation of these oxides by the alkalies. 

Grape-sugar also combines with many bases. The compounds which it forms with 
the alkalies are very unstable, and their solutions, which are at first alkaline, soon 
become neutral in consequence of the conversion of the grape-sugar into glucic acid 
(H 3 C 12 H 15 9 ) by the loss of the elements of water. 

By saturating a solution of grape-sugar with common salt, a liquid is obtained 
which deposits well-defined crystals, having the composition 2(C 6 H 12 6 ).]SraCl.H 2 0. 
When dried at 212° it becomes 2(C 6 H 12 6 ).NaCl. The true formula of grape-sugar is 
obviously C 6 H 12 6 .H 2 0, for if it be dissolved in hot strong alcohol (which dissolves 
far more grape-sugar than cane-sugar) it crystallises on cooling, in prisms, which 
have the formula C 6 H 12 6 . A molecule of water may also be expelled from ordinary 
grape-sugar at 212° F. 

The action of sulphuric acid upon cane- and grape-sugar is very different ; the 
former is carbonised and completely decomposed, whilst the latter combines with the 
sulphuric acid to form sulphosaccharic acid, which yields soluble salts with lime and 
baryta.* 

The optical properties of solutions of the sugars are now often turned to account for 
their identification, and even for the determination of their quantities. Grape-sugar 
and cane-sugar both rotate the plane of polarisation of a ray from left to right, cane- 
sugar having rather a more powerful action, but the uncrystallisable fruit-sugar 
rotates the plane in the opposite direction, from right to left. If a solution of cane- 
sugar, possessing the rotatory power from left to right, be heated with hydrochloric 
acid, it acquires the power of rotating the plane of polarisation from right to left, 
in consequence of the conversion into uncrystallisable (or inverted) sugar. 

Starch-sugar exhibits three different modes of action upon polarised light, for a 
solution which has been kept some hours rotates the plane of polarisation only half 
as much as the freshly made solution ; and if the sugar prepared from malt be dis- 
solved in water, the solution has thrice the rotatory power which it possesses after 
being kept, and its rotatory power is one-third higher than that of the freshly-dis- 
solved starch-sugar. All these may be reduced at once to the lowest rotatory power 
by heating them nearly to ebullition and allowing them to cool. 

357. Mannite (C 6 H 14 6 ), the sweet principle of manna (the concrete juice of the 
Fraxinus ornus), has already been noticed as one of the products of that peculiar 
kind of fermentation known as the viscous, to which beet-root juice is especially 
liable. It is also found in certain mushrooms, in sea-weeds, celery, asparagus, and 
onions, and as an efflorescence on the Laminaria saccharina or sugar-wrack. By 
treating manna with hot alcohol, and allowing the filtered solution to cool, the 
mannite may be obtained in beautiful prismatic crystals, which have a sweet taste, 
and dissolve readily in water. Mannite differs widely from cane- and grape-sugar in not 
fermenting when placed in contact with yeast ; and this circumstance, taken in con- 
junction with its composition, which differs so much from that of other members of 
the saccharine group, has always led to the belief that it was not properly classed 

* Ethyle-glucose, a bitter, fragrant, oily substance, has been obtained by acting upon 
grape-sugar with ethyle bromide and potash ; it may be represented by the formula 

(J 6 H 8( C 2 H 5)20 5 . 



GUN-COTTON — PYROXYLTNE. 507 

among these. Recent investigations have given it a place by the side of glycerine, 
the sweet principle of fats and oils, as will be seen hereafter. 

Glycyrrhizine, the sweet principle of the-, liquorice root, somewhat resembles man- 
nite, but does not crystallise. The sweetness of liquorice root appears to be due to 
a soluble compound of glycyrrhizine with ammonia, the glycyrrhizine itself being 
almost insoluble and tasteless. 

Sorbite, having the same composition as mannite, is a crystalline substance extracted 
from the berries of the mountain ash (Sorbus aucuparia). 

GUN COTTON AND SUBSTANCES ALLIED TO IT. 

358. Starch, the sugars, and cellulose, when acted on by the strongest 
nitric acid, furnish compounds which are remarkable for their explosive 
character. By far the most important of these is pyroxyline (irvpjlre, £v\ov, 
wood), which is produced by the action of nitric acid upon the different 
forms of woody fibre, including wood, cotton, and paper. 

If a piece of white unsized paper (filter-paper) be soaked for a few 
minutes in the strongest nitric acid (sp. gr. 1*52), then washed in a large 
volume of water and allowed to dry, it will be found to have suffered 
little alteration in appearance or texture, but to have acquired the pro- 
perty of burning very rapidly on the application of a flame or even of a 
moderately heated glass rod. This is due to the presence, in the altered 
paper, of a quantity of oxygen in the form of N0 3 , which serves to burn 
up the paper very rapidly, rendering it in great measure independent of 
any extraneous supply of oxygen. 

The pyroxyline so obtained, however, is always, associated with a quan- 
tity of unaltered paper, for water is formed by the oxidation of the 
hydrogen in the paper, and dilutes the remaining nitric acid, so that unless 
a very large proportion of nitric acid were employed, the acid would become 
so far weakened towards the close of the operation as to be incapable of 
converting the last portions of paper into pyroxyline. Moreover, since 
each fibre composing the paper is a very minute tube, often folded several 
times, it is not possible for the nitric acid to penetrate its entire substance 
unless the paper be soaked in it for a long time. 

In order to effect a more complete conversion of the woody fibre into 
pyroxyline, the nitric acid must be mixed with strong sulphuric acid, 
which will combine with the water produced by the action of the nitric 
acid upon the hydrogen of the fibre, and will thus virtually maintain the 
nitric acid at its greatest strength throughout the operation. Cotton-wool, 
from the looseness of its texture, is mere easily converted into pyroxyline 
than paper. 

The following proportions may be 
recommended for preparation of 
gun-cotton on a small scale : — Dry 
1000 grains of pure nitre (page 416) 
at a very moderate heat, place it in a 
dry retort (tig. 288), pour upon it 10 
drachms (by measure) of strong sul- 
phuric acid, and distil until 6 
drachms of nitric acid have passed 
over into the receiver. Dry some 
pure cotton- wool, and weigh out 30 
grains of it. Mix 2\ measured 
drachms of the nitric acid with an Fig. 288. 

equal volume of strong sulphuric 

acid in a small beaker. Allow the mixture to cool, immerse the cotton-wool in 
separate tufts, pressing it down with a glass rod, cover the beaker with a glass plate, 




508 MANUFACTURE OF GUN-COTTON. 

and set it aside for fifteen minutes. Lift the cotton out with a glass rod, throw it into 
at least a pint of water, and wash it thoroughly in a stream of water till it no longer 
tastes acid or reddens blue litmus paper. Dry the cotton by exposure to air or to a 
very moderate heat. 

Very great great attention has been paid to the manufacture of gun-cotton 
during the last few years, with the object of producing a perfectly uniform 
product which might be employed as a substitute for gunpowder. 

The following is an outline of the process now generally adopted for 
the production of large quantities of gun-cotton by Abel's process : — 

359. Manufacture of gun-cotton. — The cotton is employed in the form of the waste 
cuttings from spinning machines (cotton waste), and is thoroughly cleansed. 

The proportions in which it is found most advantageous to mix the nitric and 
sulphuric acids are 1 part of nitric acid (sp. gr. l - 52) and 3 parts by weight (or 2*45 
by volume) of sulphuric acid (sp. gr. 1*84). These proportions of the acids are placed 
in separate stoneware cisterns with taps, and allowed to run simultaneously, in slow 
streams, into another stoneware cistern furnished with a tap and an iron lid, through 
a second opening in which an iron stirrer is employed to mix the acids thoroughly. 
The mixture is set aside for several hours to become perfectly cool. 

A quantity of the mixed acids is drawn off into a deep stoneware pan standing in 
cold water, and provided with a perforated iron shelf, upon which the cotton may be 
drained. The well-dried cotton is immersed, a little at a time, in the acid, and 
stirred about in it for two or three minutes with an iron stirrer. It is then placed 
upon the perforated shelf, and the excess of acid squeezed out with the stirrer. 
Enough acid is drawn from the cistern to replace that which has been absorbed by 
the cotton, and more cotton is treated in the same way. Since a considerable rise of 
temperature is produced by the action of the nitric acid upon the cotton, it is neces- 
sary to keep the pan surrounded with cold water. A large proportion of the cotton 
is doubtless converted into gun-cotton in this preliminary immersion in the mixed 
acids ; but in order to convert the remainder, it is necessary to allow the cotton to 
remain in contact with the acid for a much longer period, so as to ensure its pene- 
tration into every part of the minute twisted tubes of the fibre. The preliminary 
immersion of each skein has the advantage of wetting every part with the acid, which 
could not be so certainly effected if several skeins were thrown at once into a jar, 
and of preventing the great accumulation of heat which would ensue if the entire 
chemical action were allowed to take place upon a number of skeins at the same time. 
The amount of heat evolved during the subsequent soaking in acid is comparatively 
small. 

The skeins are next transferred to a jar with a well-fitting cover, in which they are 
pressed down and completely covered with the mixed acids, of which from 10 to 15 
times the weight of the cotton will be required, according to the closeness with which 
the skeins are packed in the jar. The jar is placed in cold water, and the cotton 
allowed to remain in the acid for about twelve hours. 

The skeins are then removed, with the aid of an iron hook, to a centrifugal 
extractor, which is a cylinder made of iron gauze, through which the liquid is whirled 
out by the rapid rotation of the cylinder upon an axle. In this they are whirled, at 
first slowly, and afterwards at 800 revolutions per minute, during ten minutes, when~ 
the bulk of the acid is separated. In order to wash away the remainder of the acid, 
the cotton is plunged, suddenly, into a cascade of water ;. lor if the water were 
allowed to come slowly into contact with the mixed acids, so much heat would be 
evolved as to decompose a portion of the pyroxyline. The cotton is then drained 
in the centrifrugal extractor, and again rinsed in much water. After two or three 
rinsings it is reduced to pulp in a rag-engine such as is employed in paper-mills, The 
pulp is thoroughly washed by being well stirred up by a poaching -engine for about 
forty-eight hours in a stream of warm water, so as to remove eveiy trace of acid, 
which is assisted by rendering the water alkaline with a little lime or carbonate of 
soda or with ammonia. The pulp is then drained, moulded into discs or any other 
required form, condensed by hydraulic pressure until it has at least the same specific 
gravity as water, and dried upon heated plates. As it leaves the hydraulic press, the 
cotton contains about one-fifth of its weight of water, so that it may, if required, be 
cut up or bored without danger of explosion. 

The finished gun-cotton is examined by the following tests : — 

1. Four grains are heated in a test-tube placed in an oil-bath, and containing a slip 



COMPOSITION OF GUN-COTTON. 509 

of moistened paper imbued with potassium iodide and starch (to detect nitrous 
vapours). No tinge should be imparted to the paper till the temperature of the oil 
reaches 190° F. 

2. The experiment is repeated, omitting the test-paper, and closing the tube with 
a disk of card. No brown fumes should be perceived on looking down the axis of the 
tube below a temperature of 320° F. 

3. One grain is heated in a test-tube placed in an oil-bath till it explodes, which 
should not happen below 343° F. 

4. The gun-cotton should dissolve entirely in acetic ether, which would leave any 
unconverted cotton undissolved. 

5. Fifty grains of the gun-cotton should suffer little loss in weight when digested 
for two or three hours with four ounces of a mixture of 1 volume alcohol and 2 volumes 
ether, which would dissolve any collodion-cotton. 

360. Chemical composition of gun-cotton. — Perfectly pure gun-cotton 
contains carbon, hydrogen, nitrogen, and oxygen, in proportions which, 
correspond to the empirical formula C 6 E 7 N 3 O n . The determination of 
its rational formula is attended with difficulty, because, being an indiffer- 
ent substance, it does not form definite combinations with other bodies 
of known molecular weight, and it is, of course, impossible to arrive at its 
volume in the state of vapour which, so frequently affords valuable assist- 
ance in fixing a rational formula. 

The most probable formula is C 6 H 7 2 (X0 3 ) 3 , which represents it as the 
nitric ether of cellulose, according to which view cellulose is a triatomic 
alcohol, C 6 H 7 2 (OH) 3 , to which gun-cotton has the same relation as nitric 
ether, C 2 H 5 N0 3 , has to alcohol C 2 H.(OH). The action of nitric acid upon 
the cotton would then be represented by the equation— 

C 6 H 7 2 (OH) 3 + 3HXO s = 3H 2 + C 6 H 7 2 (N0 3 ) 3 

Cellulose. Cellulo-trinitrine. 

If gun-cotton be digested, at a gentle heat, for about fifteen minutes, in an 
alcoholic solution of KHS (prepared by dissolving KHO in alcohol and 
thoroughly saturating with H 2 S) it is reconverted into cellulose — 

C 6 H 7 2 (X0 3 ) 3 + 3KHS - C 6 H 7 2 (OH) 3 + 3KN0 2 + S 3 

Gun-cotton. Cellulose. Potassium nitrite. 

If gun-cotton were trinitroceUulose, C 6 H 7 (X0 2 ) 3 5 , the action of KHS 
might be expected to convert it into an organic base, just as it converts 
nitrobenzene C 6 H 5 (X0 2 ) into aniline C 6 H 5 (jSrH 2 ). 

361. Products of the explosion of gun-cotton. — From what has been 
stated with respect to the products of explosion of gunpowder (page 422), 
it might be expected that those furnished by gun-cotton would vary accord- 
ing to the conditions under which the explosion takes place. When a 
mass of the gun-cotton wool is exploded in an unconfined state, the 
explosion is comparatively slow (though appearing to the eye almost in- 
stantaneous), since each particle is fired by the flame of that immediately 
adjoining it, the heated gas (or flame) escaping outwards, so that some 
time elapses before the interior of the mass is ignited. But when the 
gun-cotton is enclosed in a strong case, so that the flame from the portion 
first ignited is unable to escape outwards, and must spread into the interior 
of the mass, this is ignited simultaneously at a great number of points, 
and the decomposition takes place far more rapidly: a given weight of 
cotton being thus consumed in a much shorter time, a far higher tempera- 
ture is produced, and the ultimate results of the explosion are much less 
complex, as would be expected from the well-known simplifying effect of 
high temperatures upon chemical compounds. 



510 PRODUCTS OF EXPLOSION OF GUN-COTTON. 

If a tuft of gun-cotton wool be placed at the bottom of a tall glass cylinder, and 
inflamed by a heated wire, it will be seen that, immediately after the explosion, the 
gas within the cylinder is colourless, but it soon becomes red, showing that nitric 
oxide was present among the products, and became converted into nitric peroxide by 
the oxygen of the air. The water formed by the combustion of the hydrogen converts 
the nitric peroxide into nitrous and nitric acids (p. 145), and hence the acid character of 
the moisture deposited in the barrel of a fowling-piece in which gun-cotton cartridges 
are employed. 

A little hydrocyanic acid can be detected among the products of combustion of 
loose gun-cotton. 

The determination of the products of explosion of confined gun-cotton 
has been effected by Karolyi, by enclosing the cotton in a cast-iron cylinder, 
strong enough to resist bursting until the combustion of the last portion 
of the charge, which was suspended in an iron globe exhausted of air, 
and exploded by the galvanic battery; the total volume of the gases 
collected in the globe was then determined and subjected to analysis. 
The amount of gun-cotton fired was about 10 grammes. Unfortunately, 
the formula given for the sample of gun-cotton experimented on does not 
represent pure gun-cotton, being C 12 H l7 N 5 19 , instead of C 12 H 14 N 6 22 
(representing 2 molecules of cellulo-trinitrine), so that it probably con- 
tained some unconverted cotton. 

One gramme of gun-cotton gave a quantity of aqueous vapour and 
gaseous products, calculated to occupy, at 0° C. and 760 mm. Bar.. 
753 cubic centimetres, supposing the aqueous vapour to remain uncon- 
densed at that temperature. The analysis of the gas proved that 100 
volumes of the products of explosion contain — ■ 



Aqueous vapour, 


25-34 volu 


mes 


Carbonic oxide (CO), . 


28-95 


, 


Carbon dioxide (C0 2 ), 


20-82 


, 


Nitrogen, . 


12-67 


; 


Hydrogen, 


3-16 


, 


Marsh gas (CH 4 ), 


7-24 


, 



98-18 
If the marsh gas and hydrogen be left out of consideration, the follow- 
ing equation will account for the other products of the explosion, suppos- 
ing the gun-cotton to be pure — 

2C 6 H 7 2 (N0 8 ) 3 = 9CO -t- 3C0 2 + 7H 2 + N 6 . 
According to this equation, 1 gramme of gun-cotton should furnish 829 
cubic centimetres of gas and vapour, and the volume of the products 
should be — 

Aqueous vapour, ... 28 volumes, 
Carbonic oxide, . . . 36 ,, 
Carbon dioxide, . . . 12 ,, 
Nitrogen, . . . . 12 ,, 

which do not agree with the experimental results. It is not to be ex- 
pected, however, that one simple equation should correctly represent all 
the products of such a decomposition (see page 422). 

A cubic centimetre of compressed gun-cotton, of the same density as 
water, weighs 1 gramme, and would evolve, according to the above equa- 
tion, 829 cubic centimetres of gas and vapour at 0° C, supposing the 
steam to be capable of remaining uncondensed. 

The quantity of heat generated in the explosion of gun-cotton has been 
determined by Roux and Sarrau at 1056*3 centigrade units. The specific 
heat of the products of explosion would be 0-2855. This would give 



234 cub. 


cent. 


234 „ 




166 „ 




107 „ 





DETONATION OF GUN-COTTON. 511 

3700° C. for the temperature of the gas at the moment of explosion; at 
this temperature, the 829 cubic centimetres of gas evolved by 1 gramme 
of gun-cotton would become expanded to 12,064 cubic centimetres, exert- 
ing a pressure of 81 tons per square inch if the gramme of gun-cotton 
occupies one cubic centimetre. The experiments of Noble and Abel have 
indicated 4400° C. as the temperature of explosion, and a pressure con- 
siderably more than double that produced by gunpowder when fired in a 
space which is entirely rilled by the charge. 

Sarrau and Vieille, employing a gun-cotton containing 3 parts of 
cellulo-trinitrine and 1 part of cellulo-dinitrine, C 6 H 7 2 .OH.(N0 3 ) 2 , ob- 
tained, per gramme of gun-cotton — 

Carbonic oxide, . 

Carbon dioxide, . 

Hydrogen, . ... 
Nitrogen, 

Total, . . . . 741 

At low pressures, steam was also produced, together with more carbonic 
oxide and less carbon dioxide. 

Berthelot estimates the pressure produced by the detonation of gun- 
cotton, compressed to a density of 1*1, at 24,000 atmospheres, or about 
160 tons per square inch, being only half the pressure assigned by him 
to the detonation of mercuric fulminate. 

The experiments hitherto made have been unfavourable to the employ- 
ment of gun-cotton as a substitute for gunpowder in artillery, on account 
of the injury which its violent explosion occasionally inflicts upon the 
gun. For use in fowling-pieces, the gun-cotton pulp is diluted with a 
proportion of ordinary cotton pulp, and made into a kind of paper which 
is rolled up to form the cartridges. Although such cartridges leave a con- 
siderable carbonaceous residue when fired on a plate, they leave little or 
no residue when fired under pressure. 

If a piece of compressed gun-cotton be kindled with a hot wire, it 
burns rapidly away, producing a large volume of flame, but without any 
explosive effect.* In order that gun-cotton fired in this manner might 
be used for destructive purposes, it was found necessary to confine it in 
strong cases, so that the flame of the portion first ignited should be em- 
ployed in raising the temperature of the rest to the exploding point. 

The discovery, made by E. O. Brown, of a method by which the uncon- 
fined gun-cotton could be made to explode with most destructive violence, 
has opened a new career to this material, rendering it far superior to 
gunpowder for all blasting operations, torpedoes, &c. It is only neces- 
sary to explode in contact with the compressed cotton a detonating fuze, 
consisting of a little tube of quill or thin metal charged with a few grains 
of mercuric fulminate, to cause the cotton to detonate with extreme 
violence ; and such detonation can be communicated along a row of 
pieces of compressed cotton placed at short distances from each other. 

* Too nracli stress, however, should not be laid upon this as rendering gun-cotton maga- 
zines safer in case of fire than gunpowder magazines. The experiment with gunpowder 
mentioned at page 427, shows that if all the particles of an explosive be raised at once to 
nearly the inflaming point, the first particle which inflames will cause the detonation of 
the remainder. Since the inflaming point of gun-cotton is low, the above condition would 
be easily fulfilled in a conflagration. 



512 PROPERTIES OF GUN-COTTON. 

This capability of undergoing what may be termed sympathetic explo- 
sion is by no means confined to gun-cotton. Previously to Brown's dis- 
covery, Nobel had shown it to exist in the case of nitroglycerine, and 
Abel afterwards proved that most explosives, including even gunpowder, 
can be made to detonate in a similar manner. The modus operandi of 
the detonating fuze appears, from the experiments of Abel, as well as 
from those of Champion and Pellet, to consist in the influence of vibra- 
tory motion, and the nature of the motion necessary depends upon the 
nature of the explosive. That it is not a result of the action of heat 
is proved by the circumstance that wet gun-cotton may be exploded by a 
detonating fuze, so that torpedoes may be charged with a mixture of gun- 
cotton pulp and water, containing 15 per cent, of the latter, if a small 
charge of dry gun-cotton be placed in contact with the fuze. It has 
been found that the wet gun-cotton is more easily detonated when in a 
frozen state. 

The very destructive effect of the gun-cotton exploded in this way is, 
of course, due to the sudden manner in which the whole mass is resolved 
into gaseous products. 

362. Properties of gun-cotton compared ivith those of gunpowder. — 
Gun-cotton is more easily exploded than gunpowder ; the latter requires 
a temperature of at least 600° F., whilst gun-cotton may explode at 277° F., 
and must explode at 400° F. It is very difficult to explode gunpowder 
by percussion, even between a steel hammer and anvil; but gun-cotton 
invariably detonates in this way, though the explosion is confined to the 
part under the hammer. The explosion of gun-cotton is, of course, unat- 
tended by any smoke, a most important advantage in mines, the atmo- 
sphere of which is sometimes rendered almost intolerable by the smoke 
of gunpowder used in blasting, but death has been caused by the large 
amount of carbonic oxide generated by the gun-cotton. The absence of 
residue from the gun-cotton prevents the fouling of guns, and renders it 
unnecessary to sponge them after each discharge, for the amount of incom- 
bustible mineral matter present in the cotton is very small (from 1 to 2 
per cent.), and is entirely scattered by the explosion. 

It has already been mentioned that the explosion of gun-cotton does 
not impart so much heat to the metal of the gun as that of powder, the 
difference being so great that, after firing 100 rounds with gun-cotton, the 
gun was not so much heated as after 30 rounds with gunpowder. This 
important advantage of gun-cotton is probably due to the circumstance 
that the charge of gun-cotton is only one-third of the charge of powder, 
that the explosion of the former is so much more rapid, leaving less time, 
for the communication of heat to the metal, and that there are no highly- 
heated solid products left in contact with the gun. Gun-cotton wool may 
be fired upon the palm of the hand with impunity, or upon a heap of 
gunpowder without kindling it ; although it cannot be doubted that the 
temperature of the flame is really much higher than the inflaming point 
of powder. That the recoil of a gun charged with gun-cotton is only two- 
thirds of that experienced with gunpowder, is probably due to the rapidity 
of the explosion, which allows less time for overcoming the inertia of the 
gun ; the difference in recoil taking the form of strain upon the metal 
composing the gun. 

It is evident, from the consideration of its manufacture, that gun-cotton 



PREPARATION OF COLLODION. 513 

is entirely uninjured by water, so that a store of this explosive is kept 
immersed in water; whereas gunpowder is, of course, rendered useless by 
contact with water, which dissolves out the nitre. Even when exposed 
to very damp air, gunpowder is liable to injury from the effect of 
moisture in partially separating the nitre from the other ingredients, whilst 
gun-cotton only requires exposure to a dry atmosphere for a short time to 
render it fit for use. The proportion of moisture retained by gun-cotton, 
in the ordinary state of the atmosphere, is 2 per cent. 

As an objection to the employment of gun-cotton as a substitute for 
gunpowder, it has been asserted that the cellulo-trinitrine is liable to 
undergo spontaneous decomposition, which might at any time render the 
contents of a magazine unserviceable, or might even give rise to the evolu- 
tion of a sufficient amount of heat to cause an explosion. The origin of 
this objection is to be traced to the old process for preparing gun-cotton, 
in which the acids were not allowed to act upon the cotton for a sufficient 
length of time, so that the whole of the cotton was not converted into 
true gun-cotton, but some less stable substitution products were formed 
at the same time. Another cause of spontaneous alteration is the imper- 
fect washing of the gun-cotton, whereby minute traces of acid are left in 
the fibre. All recent experiments, by Abel and others, appear to have 
proved that, considering its highly complex character, pure gun-cotton is 
a very stable compound under ordinary conditions ; although, when kept 
in a moist state, it develops traces of acid products, the temperature does 
not rise to any important extent, nor is the explosive quality of the 
material at all injured. 

363. Gun-cotton is somewhat harsher to the touch than ordinary 
cotton, and becomes remarkably electrical when rubbed between the dry 
fingers. It is insoluble in alcohol and ether, as ' well as in a mixture of 
these solvents, though ordinary specimens generally yield a small per- 
centage of soluble matter when treated with a mixture of alcohol and ether, 
because they contain extraneous matters, such as the other substitution 
products to be mentioned presently. Acetic ether dissolves it, and so does 
a mixture of ordinary ether with ammonia. Strong sulphuric acid dissolves 
it without carbonisation, unless any unconverted cotton should happen to 
be present. 

364. Collodion cotton. — \Yhen cotton or paper is acted upon by a mix 
ture of nitric and sulphuric acids containing more water than is- present 
in that employed for the preparation of gun-cotton (page 508), compounds 
are formed which contain less X0 3 , and are much less combustible than 
the cellulo-trinitrine, from which they are also distinguished by their 
solubility in mixtures of alcohol and ether. 

In order to render evident the relations between these compounds and 
gun cotton, the formula of the latter must be trebled, when we have the 
following series of compounds produced by the mixture of nitric acid, 
sulphuric acid, and water, to which they stand opposite : — 



Composition of the mixed acids. 

(1) HN0 3 + H.,S0 4 

(2) HX0 3 + h;S0 4 + HH,0 

(3) HX0 3 + H2S0 4 + 2H 9 

(4) HN0 3 + H 2 S0 4 + 2£H 



Products of their action on cellulose. 

C^HaO^NOgjg 

C 18 Ho,0/X0 3 ) s 
C 18 H. 23 8 (X0 3 ) 7 
C 18 H 24 9 (N0 3 ; 6 



As might be expected, these compounds diminish in combustibility in 
proportion as the X0 3 contained in them diminishes. The second is that 

2 K 



514 XYLOIDINE NITROMANNITE. 

employed for the preparation of photographic collodion, being dissolved 
for that purpose in a mixture of ether and alcohol. 

In order to prepare the soluble cotton for collodion, 3 measured ounces of ordinary 
nitric acid (sp. gr. 1*429) are mixed with 2 ounces of water in a pint beaker. Nine 
measured ounces of strong sulphuric acid (sp. gr. 1*839) are added to this mixture, 
which is continually stirred whilst the acid is being added. A thermometer is placed 
in the mixture, which is allowed to cool to 140° F. ; 100 grains of dry cotton wool, 
in ten separate tufts, are immersed in the mixture for five minutes, the beaker being 
covered with a glass plate. The acid is then poured into another beaker, the cotton 
squeezed with a glass rod, and thrown into a large volume of water ; it is finally 
washed in a stream of water till it is no longer acid, and dried by exposure to air. 

Collodion balloons. — These balloons may be "made in the following manner : — 6 
grains of the collodion-cotton, prepared according to the above directions, are dissolved 
in a mixture of 1 drachm of alcohol (sp. gr. '835) and 2 drachms of ether (sp. gr. 725) 
in a corked test-tube. The solution is poured into a dry Florence flask, which is 
then turned about slowly, so that every part of its surface may be covered with the 
collodion, the excess of which is then allowed to drain back into the tube. Air is 
then blown into the flask through a long glass tube attached to the bellows as long 
as any smell of ether is perceptible. A pen-knife blade is carefully inserted between 
the flask and the neck of the balloon, which is thus detached from the glass all round ; 
a small piece of glass tubing is introduced for an inch or two into the neck of the 
balloon, so that the latter may cling round it. Through this tube air is drawn out 
by the mouth, until one-half of the balloon has left the side of the flask and col- 
lapsed upon the other half; by carefully twisting the tube, the whole of the balloon 
may be detached and drawn out through the neck of the flask, when it must be 
quickly untwisted, distended by blowing through the tube, tied with a piece of silk, 
and suspended in the air to dry. The average weight of such balloons is 2 grains. 

Celluloid or artificial ivory, used for combs, billiard balls, &c, is essentially com- 
pressed collodion-cotton. 

When collodion-cotton is kept for some time, especially if at all damp, 
it undergoes decomposition, filling the bottle with red fumes, and becom- 
ing converted into a gummy mass, which contains oxalic acid. 

365. Xyloidine is the name given to a highly combustible substance 
analogous to pyroxyline, which is obtained by dissolving starch in the 
strongest nitric acid, and diluting the solution with water, when the 
xyloidine falls as a white precipitate, which may be collected upon a 
filter, and washed till free from acid. The composition of xyloidine is 
C 6 H 8 3 (N0 3 ) 2 representing starch (C 6 H 10 O 5 ), in which 2 HO have been 
replaced by 2N0 3 . 

Nitromannite C 6 H 8 (N0 3 ) 6 is another explosive body of the same order, 
obtained by adding powdered mannite (C 6 H 14 6 ), in small portions, to a 
mixture of equal measures of the strongest nitric and sulphuric acids, 
which immediately dissolve it, and .presently solidify to a mass of minute 
needles of nitromannite, which may be washed with a large volume of 
water, and crystallised from boiling alcohol. Under the hammer, nitro- 
mannite explodes with a very loud report. When heated, it fuses before 
exploding. 

WINE AND SPIRITS. 

366. Wine is essentially composed of 8 or 10 parts of alcohol, with 
85 or 90 of water, together with minute quantities of certain fragrant 
ethers, of colouring matter, of potassium bitartrate, and of the mineral 
substances derived from the grape-juice. Glycerine and succinic acid 
have also been found in wines, and appear to be constant secondary pro- 
ducts of the alcoholic fermentation. 



WINES. 515 

Those wines in which the whole of the sugar has been fermented are 
known as dry wines ; whilst fruity wines still retain a considerable 
quantity of sugar. 

The preparation of wines differs from that of beer in the circumstance 
that no addition of ferment is necessary, the fermentation being spon- 
taneous. Grape juice contains, in addition to grape-sugar, vegetable 
albumen, potassium tartrate, and the usual mineral salts found in vegetable 
juices. The husks, seeds, and stalks of the grape contain a considerable 
quantity of tannin, together with certain blue, red, and yellow colouring 
matters. 

When the expressed juice remains for a short time in contact with the 
air, the albuminous substances contained in it enter upon a state of change, 
exciting the vinous fermentation in the sugar, and a scum of yeast is 
formed upon the surface. If this fermentation takes place in contact with 
the husks of the dark grapes, the alcohol dissolves the colouring matter, 
and a red wine results ; whilst for the production of white wines, the 
husks, &c, are separated previously to the fermentation, and the juice is 
exposed as little as possible to the air, 

White wines are rather liable to become ropy from viscous fermenta- 
tion, but this is prevented by the addition of a small quantity of tannin, 
which precipitates the peculiar ferment. The tannin for this purpose is 
extracted from the husks and stalks of the grapes themselves. 

Ked wines, such as port and claret, are often very astringent from the 
tannin dissolved out of the husks, &c, during the fermentation. Port 
wine, when freshly bottled, still retains in solution a considerable quantity 
of acid potassium tartrate or bitartrate of potash (KHC 4 H 4 6 ), but after 
it has been kept some time, and become more strongly alcoholic, this salt 
is deposited, together with a quantity of the colouring matter, in the form 
of a crust upon the side of the bottle. Thus a dark fruity port becomes 
tawny and dry when kept for a sufficient length of time, the sugar having 
been converted into alcohol. 

When the wine contains an excess of tartaric acid, it is customary to 
add to it some neutral potassium tartrate (K 2 C 4 H 4 6 ), which precipitates 
the acid in the form of bitartrate. 

The preparation of champagne is conducted with the greatest care. 
The juice or must is carefully separated from the marc or husk, and is 
often mixed with 1 per cent, of brandy before fermentation. After 
about two months the wine is drawn off into another cask, and clarified 
with isinglass dissolved in white wine, and added in the proportion of 
about half an ounce to 40 gallons. This combines with the tannin to 
form an insoluble precipitate, which carries with it any impurities float- 
ing in the wine. After another interval of two months, the wine is again 
drawn off, and a second clarification takes place ; and in two months 
more the wine is drawn off into bottles containing a small quantity of pure 
sugar-candy dissolved in white wine. The bottles, having been securely 
corked and wired, are laid down upon their sides for eight or ten months, 
during which time the fermentation of the newly added sugar takes place, 
and the carbonic acid produced dissolves in the wine, whilst a quantity of 
yeast is separated. In order to render the wine perfectly clear, the bottle 
is left for about three weeks in such a position that the deposit may subside 
into the neck, against the cork, which is then unwired so that the pressure 
of the accumulated carbonic acid gas may force it out together Math the 



516 WINES— DISTILLED SPIRITS. 

deposit ; the bottle having been rapidly filled up with ' white wine, is 
again corked, wired, covered with tin foil, and sent into the market. Pink 
champagne is prepared from the must which is squeezed out. of the marc 
after it has ceased to run freely, and contains a little of the colouring matter 
of the husk. The colour is also sometimes imparted by adding a little 
tincture of litmus. 

The proportion of alcohol in wines varies greatly, as will be seen 
from the following statement of the weight of alcohol in 100 parts of the 
wine : — 



Port, . 


15 to 17 


Claret, . 


8 to 9 


Sherry, 


14 to 16 


Eudesheimer, . 


7 to 8-5 


Champagne, . 


11-5 







Sherry contains from 1 to 5 per cent, of sugar, port from 3 to 7 per 
cent., and Tokay 17 per cent.; in the last case, the sugar is increased 
by adding some of the must, concentrated by evaporation, to the wine 
previously to bottling. 

The bouquet or fragrance of wine is due to the presence of certain 
fragrant ethers, especially of oenanthic, pelargonic, and acetic ether, formed 
during the fermentation or during the subsequent storing of the wine. 
It is to the increased quantity of such fragrant ether that the superior 
bouquet of many old wines is due. 

367. Distilled spirits. — The' varieties of ardent spirits are obtained 
from fermented liquids by distillation, so that they consist essentially of 
alcohol more or less diluted with water, and flavoured either with some 
of the volatile products of the fermentation, or with some essential oil 
added for the purpose. 

Brandy is distilled from wine, and coloured to the required extent 
with burnt sugar (caramel). Its flavour is due chiefly to the presence 
of oenanthic ether derived from the wine. The colour of genuine pale 
brandy is due to its having remained so long in the cask as to have dis- 
solved a portion of brown colouring matter from the wood, and is. there- 
fore an indication of its age. Hence arose the custom of adding caramel, 
and sometimes infusion of tea, to impart the colour and astringency due 
to the tannin dissolved from the wood by old brandy. 

Whisky is distilled from fermented malt, which has been dried over a 
peat fire, to which the characteristic smoky flavour is due. 

Gin is also prepared from fermented malt or other grain, and is 
flavoured with the essential oil of juniper, derived from juniper berries 
added during the distillation. 

Rum is distilled from fermented molasses, and appears to owe its 
flavour to the presence of butyric ether, or of some similar compound. 

Arrack is the spirit obtained from fermented rice. 

KirscJuvasser and maraschino are distilled from cherries and their stones, 
which have been crushed and fermented. 

Some varieties of British brandy and whisky are distilled from fer- 
mented potatoes, or from a mixture of potatoes and grain, when there 
distils over, together with ordinary alcohol, another spirit belonging to 
the same class, but distinguished from alcohol by its nauseous and 
irritating odour. This substance, which is known as potato-spirit, amylic 
alcohol, oy f ousel oil (C 5 H 12 0), also occurs, though in very minute quantity, 
in genuine wine-brandy. The manufacturers of spirit from grain and 



THE ALCOHOLS AND THEIR DERIVATIVES. 517 

potatoes remove a considerable part of this disagreeable and unwhole- 
some substance by leaving the spirit for some time in contact with wood- 
charcoal. 

THE ALCOHOLS AT\ T D THEIR DERIVATIVES. 

368. It was stated at page 437 that the alcohols are constructed upon 
the model of water in which one-half of the hydrogen is replaced by a 
compound radical; e.g., methyle alcohol, H 3 C.OH, in which methyle, 
H 3 C, occupies the place of the atom of H in HOH or H 2 0. 

The alcohols are designated as monatomic, diatomic, triatomic, and so 
on, accordingly as they are constructed upon the model of 1, 2, 3, or 
more molecules of water. 

Model or Type. Alcohol. 

H 2 = H.OH H 3 C.OH monatomic {Methyle alcohol). 

2H 2 = H 2 (OH) 2 H 4 C 2 (OH) 2 diatomic {Ethylene glycol). 

3H 2 = H 3 (OH) 3 H 5 C~(OH) 3 triatomic {Glycerine). 
&c. &c. 

Hence, a monatomic alcohol contains one hydroxyle group (OH), a diatomic 
alcohol contains two, and a triatomic alcohol contains three hydroxyle 
groups. 

Monatomic Alcohols. — The simplest type of these is the methylic 
alcohol (carhinol), H 3 C.OH. The H contained in the hydroxyle group is 
termed typical hydrogen, because it cannot be changed without altering 
the type upon which the alcohol is formed; but the H in the methyle 
(H 3 C), or methylic hydrogen, admits of replacement, and it is in this way 
that the different monatomic alcohols are produced. 

The monatomic alcohols are again subdivided into primary, secondary, 
and tertiary, accordingly as 1, 2, or 3 atoms of the methylic hydrogen in 
the type have been replaced in order to form the alcohol — 

Model or Type, HHHC.OH Carbinol. 

Primary butylic alcohol, (C 3 H 7 )HHC.OH Propylcarbinol. 

Secondary ' ,, (C 9 H 5 )(CH 3 )HC.OH M ethyl -ethyl-carbinol. 

Tertiary „ (CH 3 KCH 3 )(CH 3 )C.OH Trimethyl-carbinol. 

It will be seen that these three alcohols have the same molecular formula, 
C 4 H 10 O, but their properties are quite different — 

Primary butylic alcohol, liquid, boiling at 116° C. 
Secondary ,, „ ,, 99° C. 

Tertiarv solid i fusin S at 25 ° C ' 

iertiai > » SOild ' j boiling at 82°'5 C. 

Alcohols are said to be normal when their carbon-atoms are so united 
as to form a single chain with one carbon atom at each end. Thus, normal 

butylic alcohol is h7h7h7h 2 .OH. 

The iso-alcohols have the same composition as the normal alcohols (tcros, 
equal,) but some of their carbon-atoms form side-chains, so that there are 
more than one carbon-atom at one end of the chain. This is seen in 

isobutylic alcohol, TT 3 p/-rT ^ qtt 

It is obvious that the number of possible iso-alcohols will increase with 
the number of carbon-atoms. 

The monatomic primary alcohols are the most numerous and important. 



518 



MONATOMIC ALCOHOLS. 



Monatomic primary alcohols. — The following table includes the chief 
alcohols of this series which are at present known : — 



Chemical Name. 


Source. 


Formula. 


Common Name. 


1. Methylic alcohol, 


Destructive distillation of wood, 


C H 4 


Wood-naphtha 


2. Ethylic 


Vinous fermentation of sugar, 


C 2 H 6 


Spirit of wine 


3. Propylic ,, 


Fermentation of grape-husks, 


C 3 H 8 




4. Butylic ,, 


Fermentation of beet-root, . 


C 4 H 10 O 




5. Amylic ,, 


Fermentation of potatoes, 


C 5 H I2 


Fousel oil 


6. Caproic ,, 


Fermentation of grape-husks, 


C 6 H 14 




7. CEnanthic ,, j 


Distillation of castor oil with > 
potash, . . '. . j 


C 7 H 16 




8. Caprylic ,, 


Fermentation of grape-husks, 


C 8 H 18 




10. En tic ,, 


Oil of rue, .... 


CioH. 22 




12. Laurie ,, 


Whale oil, .... 


C 12 H 26 




16. Cetylic ,, 


Spermaceti, 


C 16 H, 4 


Ethal 


27. Cerylic ,, 


Chinese wax, 


C 2 7H 56 


Cerotene 


30. Melissic ,, 


Bees' wax, . . ... 


C3oH 62 


Melissine 



The regular increase of these alcohols by the addition of CH 2 is explained 
by the successive replacements of H by CH 3 (methyle). Thus, by replac- 
ing H in H 2 0, we obtain CH 3 .HO, or CH 4 ; by again replacing H in 
the CH 3 , we obtain CH 2 (CH 3 ),* HO, or C 2 H 6 0, &c. (see page 438). 

The usual gradation in properties attending the gradation in composition 
among the members of a homologous series, is strikingly exemplified in 
the class of alcohols. Methylic, ethylic, propylic, butylic, amylic, caproic, 
oenanthic, and caprylic alcohols, are all liquid at the ordinary temperature ; 
they all possess peculiar and powerful odours, and may be readily distilled 
unchanged. The two first, methylic and ethylic alcohols, may be mixed 
with water in all proportions, but the third, propylic alcohol, though freely 
soluble in water, is not so to an unlimited extent ; whilst butylic alcohol 
is less soluble, and amylic alcohol may be said to be sparingly soluble in 
water. Caproic alcohol, the next member, is insoluble in water ; whilst 
caprylic is not only insoluble, but possesses an oily character, leaving a 
greasy stain upon paper. 

In their boiling-points, and the specific gravities of their vapours, a 
similar gradation is observed. 



Alcohol. 


Boiling-Point. 


Vapour Density. 


Methylic, 


151° F. 


1-12 


Ethylic, . ... • . 


173° 


1-61 


Propylic, 


206° 


2-02 


Butylic, 


233° 


2-59 


Amylic, 


269°'8 


- 3-15 


Caproie, . 


299°-309° 


3-53 


03nanthic, . 


327°-343° 




Caprylic, 


356° 


4-50 



One molecule of each of these alcohols yields two volumes of vapour ; 
or, in other words, if a given weight of the alcohol corresponding to its 
molecular weight be converted into vapour, that vapour will occupy twice 
as much space as would be occupied by one part by weight of hydrogen 
at the same temperature and pressure. 

The higher members of the group of alcohols are solid fusible bodies 
more nearly approaching to waxy or fatty matters in their nature, and 



ACETIC SERIES OF ACIDS. 



519 



not susceptible of distillation without decomposition. Far less is known 
of these than of the alcohols containing less carbon. 

The true chemical definition of an alcohol of this series rests upon the 
circumstance, that under the influence of oxidising agents, it first parts 
with 2 atoms of hydrogen, and is converted into an aldehyde (alcohol 
dehydrogenated), and afterwards absorbs an atom of oxygen, yielding an 
acid. Thus, it has been already shown (page 498) that vinic alcohol 
(C 2 H 6 0), when exposed to air under favourable conditions, yields alde- 
hyde, C 2 H 4 0, which, by absorbing oxygen, is converted into acetic acid, 
C 2 H 4 2 . 

The formation of an aldehyde would, therefore, be represented by the 
general formula — 



G.H, 



!n+2 + O = C M H 2n O + H 2 

Alcohol. Aldehyde. 



and that of the corresponding acid by 



C n H 2M+2 + 2 

Alcohol. 



— C w H 2m 2 

Acid. 



+ H,0 



In addition to this, a double molecule of each of these alcohols, by 
the loss of the elements of a molecule of water, yields an ether, corre- 
sponding to ordinary ether (C 2 H 5 ) 2 0, which differs from the double 
molecule of vinic alcohol, C 9 H 6 0, by the elements of a molecule of 
water. 

The general formula representing the derivation of an ether from an 
alcohol of the above series is — 



2C„H 2M+2 - H 2 

Alcohol. 



(C M H 2w+1 ) 2 0. 

Ether. 



Hence, every alcohol has its corresponding aldehyde, acid, and ether, 
so that there are homologous series of aldehydes, acids, and ethers, just 
as of the alcohols from which they are derived. 

The only members of the aldehyde and ether series which have received 
a large share of attention on account of their practical importance, are 
those derived from ordinary alcohol ; but the series of acids contain many 
members of importance, to some of which no corresponding alcohols are 
yet known. 

The very important homologous series of acids* composed after the 
general formula C n H 2w 2 , includes — 



Acid. 


Source. 


formula. 


1. Formic acid, 


Red ants, nettles, 


C H 2 0. 2 


2. Acetic ,, 


Vinegar, .... 


C 2 H 4 


3. Propylic ,, 


Oxidation of oils, 


c 3 h 6 o; 


j 4. Butyric ,, 


Rancid butter, . 


C 4 H 8 2 


j 5. • Valerianic acid, 


. Valerian root, . 


C 5 H 10 O 2 


6. Caproic ,, 


Rancid butter. . 


C 6 H 12 2 


7. CEnanthic ,, 


Oxidation of castor oil, 


C 7 H 14 2 


8. Caprylic ,, 


Rancid butter, . 


Cg H 16 2 


9. Pelargonic ,, 


Geranium leaves, 


C 9 H 18 2 


10. Rutic or capric acid, 


Rancid butter, . 


C10H20O2 


11. Euodicf 


Oil of Rue, . 


C u H 22 2 


12. Laurie ,, 


Bay berries, 


C 12 H 24 2 



* Often spoken of as the acetic series of acids, or the fatty acid series. 
*T Euwotjs, fragrant. 



1)20 



FATTY ACIDS. 



Homologous Series of Acids- 



-continued. 



Ackls. 


Source. 


Formula. 


13. Cocinic acid, 


Cocoa nut oil, . 


C13H26O2 


14. Myristic „ 


Nutmeg butter, 


Ci 4 H 28 2 


15. Benic ,, 


Oil of beu, 


V15**30^2 


16. Palmitic ,, 


Palm oil, .... 


^16^3-2^2 


17. Margaric ,. 


Olive oil (?), . 


C 17 H 34 2 


18. Stearic ,, 


Tallow, .... 


Ci8H 36 2 


19. Balenic 




^19 "38^2 


20. Butic(arachidic),, 


Earth nut, ... 


^ 20 " 40^2 


21. Nardic ,, 




^21 42 2 


22. Behenic „ 




C 22 H 44 2 


25. Hyamie ,, 




C25H50O2 


27. Cerotic 


Bees' wax, . . 


C 2 7"54^2 


30. Melissic „ 


Bees' wax, 


^30^60^2 



The type of this series of acids is formic acid H(OC.OH) = CH 2 2 , 
which may be represented as composed of hydrogen and the radical 
oxatyle (OC.OH) (see page 437) ; this radical remains unchanged through- 
out the whole series, the different acids being produced by successive 
replacements of the external hydrogen. Thus acetic acid is H 3 C.OCOH, 
or methyle-formic acid, propylic acid is H 5 C 2 .OCOH, or methyl-acetic acid, 
and so on. 

It is by the replacement of the H in the oxatyle group by metals that 
these acids are converted into salts, and therefore all the acids of this 
series are monobasic (page 250). 

A very gradual transition of properties is observable in the members of 
this extended series of acids. 

The first nine members of the series are liquid, the remainder solid at 
common temperatures. Of the liquids, formic acid boils at 212° F., and 
the boiling-points of the other members exhibit a gradual rise up to pelar- 
gonic acid, which boils at 500° F. The melting-points of the solid acids 
also ascend from 86° F. for rutic acid (C 10 H 20 O 2 ) to 192° F. for melissic 
(C 3 oH 60 2 ). 

Formic and acetic acids may be mixed with water in all proportions, 
like their corresponding alcohols, the methylic and ethylic ; propylic 
acid, though soluble to a great extent in water, resembles the correspond- 
ing alcohol in not mixing indefinitely with water. Butyric acid behaves 
in a similar manner. Valerianic, caproic, oenanthic, and caprylic acids are 
sparingly soluble in water. Pelargonic and capric acids are very sparingly 
soluble, and the remaining members of the series are very decidedly fatty 
acids, insoluble in water, and forming soaps with the alkalies. 

The members of the series of alcohols, under the action of powerful 
dehydrating agents, are capable of parting with the elements of a mole- 
cule of water, furnishing the members of a homologous series of hydrocar- 
bons related to their corresponding alcohols, as olefiant gas or ethylene 
(C 2 H 4 ) is related to ethylic alcohol. 

The general formula for the production of the homologues of ethylene 
(or olefines) from the alcohols may be thus expressed — 

C„H 2»+aO - H 2 = C n H 2n 



ALCOHOL. 



521 



The chief known members of this series of hydrocarbons are-- 



Name. 


Formula. 


Corresponding 
Acid. 


Corresponding 
Alcohol. 


2. Ethylene, 


C,H 4 


Acetic 


Alcohol 


3. Propylene,* 

4. Butylene, 

5. Amylene, 


C 3 H 6 
C 4 H 8 
C 5 H 10 


P ropy lie 
Butyric 
Valerianic 


Propylic 
Butylic 
Fousel oil 


6. Caproylene, 

7. (Enanthene, . 


^6 H 12 

C 7 H 14 


Caproic 
(Enanthic 


Caproic 
(Enanthic 


8. Caprylene, 

9. Elaene, . 

10. Paramylene, . 


^8 Hlfi 

CioH 2 o 


Caprylic 

Pelargonic 

Eutic 


Caprylic 
Eutic 


16. Cetylene, 


C 16 H 32 


Palmitic 


Ethal 


27. Cerotene, 


C 27 H 54 


Cerotic 


Cerotene 


30. Melissene, 


^30^60 


Melissic 


Melissine 



Of these hydrocarbons, ethylene and propylene are gaseous; butylene is 
also a gas, but easily condensed to a liquid state ; the remainder are liquid 
at the ordinary temperature, except cerotene and melissene, which are solid. 

Since one molecule of each of these hydrocarbons in the state of vapour 
occupies two volumes, it must follow, if their composition be correctly 
stated, that their vapour densities exhibit a progression similar to that 
which exists in the formulas. 

That this is the case will be seen by the subjoined table, which illus- 
trates very clearly the importance of determining the specific gravity of 
the vapour of a volatile substance as a confirmation of the results of 
analysis :■ — 



Hydrocarbon 


. 


Specific gravity 
of vapour. 


Ethylene, 


C,H 4 


. 0-978 


Propylene, 


QjHe 


. 1-498 


Butylene, 


C 4 H 8 


. 1'852 


Amylene, 


CsH 10 


. 2-386 


Caproylene, 


C 6 H 12 


. 2-874 



Hydrocarbon. 

Caprylene, 
Elaene, 
Paramylene, 
Cetylene, 



CgHj 
C Q H n 



Specific gravity 
of vapour. 
3-90 
4-48 
5-061 
8-007 



It will be seen hereafter that each of these defines is capable of giving 
rise to a diatomic alcohol or glycol, derived from a double molecule of 
water, in which 2 atoms of hydrogen are replaced by an olefin e ; thus, 
(C 2 H 4 )H 2 2 is ethylene glycol, (C 3 H 6 )H 2 2 is propylene-glycol. 

369. Alcohol may be studied as the type of the class to which it gives 
a name. 

When any of the fermented or distilled liquors of commerce are sub- 
jected to distillation, the alcohol passes over during the first part of the 
process, mixed with a considerable quantity of water ; and if the distilla- 
tion be continued as long as any alcohol passes over, and the whole of the 
distilled liquid be measured or weighed, the quantity of alcohol present 
in the original liquid subjected to distillation, may be inferred (by refer- 
ence to a table) from the specific gravity of the aqueous spirit distilled 
from it, since the lighter it is the more alcohol it contains, the specific 
gravity of pure alcohol being 0*794. 

* These hydrocarbons are sometimes designated by names which refer to the multiple of 
H!H 2 which they contain. Thus propylene, 3(CH 2 ), is sometimes called tritylene ; buty- 
lene, tetrylene ; caproylene, hexylene, &c. 



522 ALCOHOL — ETHER. 

The strength of the spirit of wine of commerce is ascertained by deter- 
mining its specific gravity. Spiritus rectificatus has the specific gravity 
•838, and contains 84 per cent, by weight of alcohol. That known as 
proof spirit (spiritus tenuior) has the specific gravity 0'9 20, and is so 
called because it is the weakest spirit which will answer to the rough 
proof of firing gunpowder which has been moistened with it and kindled. 
Any spirit weaker than this leaves the powder moist, and does not explode 
it. It is then said to be under proof, whilst a stronger spirit is spoken 
of as over proof . 

Proof spirit contains by weight, in 100 parts, 50*76 of water, and 49*24 
of alcohol. 

A spirit would be spoken of as 30 per cent., for example, over proof , 
if 100 measures of it, when diluted with water, would yield 130 measures 
of proof spirit. A spirit 30 per cent, below proof contains, in every 100 
measures, 70 measures of proof spirit. By repeatedly rectifying or redis- 
tilling the weak spirit obtained from a fermented liquid, collecting the 
first portions separately, a strong spirit may be obtained, containing 90 
per cent, of alcohol, but mere distillation will not effect a further separa- 
tion of the water. Weak spirit may be concentrated to a greater extent 
than this, by leaving it enclosed in a bladder for a considerable period, 
when the water exudes through the bladder more readily than the alcohol, 
so that the latter accumulates in the mixture to the amount of 95 percent. 

Another method of separating a great part of the water consists in add- 
ing dry potassium carbonate to the weak spirit as long as it is dissolved, 
when the mixture separates into two layers, the lower consisting of solu- 
tion of the carbonate in water, and the upper one of spirit, containing 89 
per cent, of alcohol. By effecting the separation in a graduated tube, 
this method is sometimes employed for roughly ascertaining the proportion 
of alcohol in a fermented or distilled liquid, the foreign matters in which 
prevent any safe inference from the specific gravity. 

The last portions of water are removed from alcohol by allowing it to 
stand for two or three days over powdered quicklime, and distilling, when 
the lime retains the water in the form of calcium hydrate, and the pure or 
absolute alcohol distils over. It must then be preserved in well-stopped 
bottles, since it readily absorbs moisture from the atmosphere. Its attrac- 
tion for water causes it to evolve heat when mixed with that liquid, and 
the volume of the mixture is less than the sum of the volumes of its 
components, showing that combination has taken place. 

Pure alcohol does not freeze ; but the compound C 2 H 6 0. 4H 2 crystal- 
lises at - 34° C. When a weak spirit is cooled, ice separates until this 
ratio is reached, when the temperature remains constant till the whole has 
solidified. 

370. Ether, or, as it is sometimes erronously called, sulphuric ether 
(C 4 H 10 O), is obtained by distilling a mixture of two measures of alcohol 
with one measure of concentrated sulphuric acid. As soon as the mixture 
begins to blacken, in consequence of a secondary decomposition of the 
alcohol, the retort is allowed to cool, another half measure of alcohol is 
added, and the mixture again distilled as long as ether is obtained. 

A far better method of obtaining ether is that known as the continuous 
process. Alcohol of sp. gr. 0'830 is mixed with an equal measure of con-* 
centrated sulphuric acid, and introduced into a retort or flask (fig. 289), 



PREPARATION OF ETHER. 



523 



which is connected with a small cistern containing alcohol. The mixture 
in the flask is rapidly raised to the boiling-point, and alcohol is allowed to 
pass slowly in from the reservoir through a siphon furnished with a stop- 
cock, so as to keep the liquid in the flask at a constant level. A thermo- 
meter should be immersed in the liquid, the temperature of which should 
be maintained at 284° to 290° F. (140° to 143° C). By this process, one 
measure of sulphuric acid will effect the conversion into ether of thirty 
measures of alcohol. The boiling-point of ether being very low (94° '8 F., 
35° C.) necessitates the employment of a good condensing arrangement. 




Fig 289,— Continuous etlierification. 

The liquid which distils over contains about two-thirds of its weight 
of ether, with about one-sixth of water, and an equal quantity of alcohol. 
Traces of sulphurous acid are also generally present. To obtain the pure 
ether, it is shaken with water containing a little potassium carbonate, when 
the water dissolves the alcohol, and the potash removes the sulphurous 
acid ; the ether being very sparingly soluble in, and much lighter than 
water (sp. gr. - 74 at 0° C), rises to the surface, holding a little water in 
solution. This upper layer is drawn off and freed from water by distilla- 
tion in a water-bath, at a very low heat, over quicklime. 

The explanation of the chemistry of this process of etlierification will 
be more intelligible after some other changes to which alcohol is liable 
have been studied. 

The most striking properties of ether are its peculiar odour and its 
great volatility ; its rapid evaporation when poured upon the hand gives 
rise to a sensation of intense cold; and if a little ether be evaporated by 
blowing upon it in a watch-glass with a drop of water hanging from its 
convexity, the water will be speedily frozen. Ether is also exceedingly 
inflammable ; and since its vapour is very heavy (sp. gr. 2 "59), and passes 
in an unbroken stream through the air for a considerable distance, great 
care should be taken to avoid pouring it from a bottle in the neighbour- 
hood of a flame. Its flame is far more luminous than that of alcohol, and 
much acetylene is produced during its imperfect combustion (page 94). 

The high specific gravity, volatility, and inflammability of ether vapour admit of 
illustration by some curious experiments : — 



524 THE ALCOHOL- RADICALS. 

A piece of tow wetted with ether is placed at the top of a sloping wooden trough 
over 6 feet long ; a match applied at the lower end fires the train of vapour. 

If a small piece of sponge be saturated with ether and placed in the centre of a 
large wooden tray, 2 or 3 inches deep, the latter will soon be entirely tilled with the 
vapour, as may be shown by applying a lighted match to one corner. A jug may be 
warmed by rinsing a little hot water round it, and this having been thrown out, a 
few drachms of ether may be poured into the jug, which will immediately become 
filled with ether vapour, and from this several glasses may. be filled in succession, the 
presence of the ether vapour beiug proved by a lighted taper. 

A pneumatic trough may be filled with warm water, a small test-tube filled with 
ether inverted with its mouth under the water, and the ether quickly decanted up 
into a gas jar also filled with hot water, where it will be immediately converted into 
vapour, and may be decanted through the water into other vessels, and dealt with 
like a permanent gas. Some cold water poured over the jar containing it at once 
proves its condensible character. 

When ether is acted upon by hydrochloric, hydrobroniic, or hydriodic 
acid, the oxygen of the ether enters into combination with the hydrogen 
of the acid, and the chlorine, bromine, or iodine occupies its place. 

Thus, with hydrochloric acid — 

(C 2 H 5 } 2 {Ether) + 2HC1 = 2C 2 H 5 C1 (Hydrochloric ether) + H 2 . 
In a similar manner, hydrobromic ether, C 2 H 5 Br, and hydriodic ether, 
C 2 H 5 I, may be formed. The best method of obtaining the two last, how- 
ever, consists in distilling moderately strong alcohol with phosphorus and 
either bromine or iodine, when orthophosphoric acid and hydriodic ether 
are formed — 

5(C 2 H 5 .OH) + P + I 5 = 5C 2 H 5 I + H 3 P0 4 + H 2 0. 

,, , . Orthophosphoric 

Alcohol. a £ id 

These three ethers are colourless, fragrant, volatile liquids, which are 
of the greatest value in the investigation of the constitution of complex 
organic compounds. 

This remark applies particularly to hydriodic ether (ethyle iodide), which 
is less volatile than the others, and therefore more easily manageable in 
experiments requiring a high temperature. 

Iodide of ethyle, or ethylic iodide, is prepared by distilling 1^00 grains of ordinary 
alcohol (sp. gr. 0"84) with 2000 grains of iodine, and 100 grains of ordinary vitreous 
phosphorus. The iodine and phosphorus are added alternately, in small portions, to 
the alcohol in the retort, which is immersed in cold water to moderate the action, 
and occasionally shaken. When the whole has been added, the retort is connected 
with a Liebig's condenser, and heated in the water-bath, when about 2| measured 
ounces of ethyle iodide mixed with alcohol will pass over. This is shaken in a 
stoppered bottle with about an equal measure of water, which dissolves the alcohol, 
leaving the ethyle iodide to collect at the bottom as an oily layer (sp. gr. 1"97). 
After as much as possible of the upper aqueous layer has been removed with a siphon 
or pipette, the iodide is poured into a small retort containing- fused calcium chloride in 
powder to remove the water. The retort is closed with a cork, and set aside for some 
hours, when the ethyle iodide may be distilled off in the water-bath, and condensed 
in a Liebig's condenser. 

Another process consists in placing 1 part of amorphous phosphorus and 5 parts of 
alcohol in a retort, adding gradually 10 parts of iodine in. powder, setting aside for 
twelve hours, and distilling. 

371. Alcohol-radicals. — If ethylic iodide be poured over granulated 
zinc contained in a stout glass tube, which is then exhausted of air, 
hermetically sealed, and heated for two hours in an oil-bath to 300° F., 
a crystalline substance is deposited, which is a compound of zinc iodide 
with zinc ethyle (C 2 H 5 ) 2 Zn, whilst a colourless liquid separates, consist- 
ing of a mixture of three hydrocarbons, which have been liquefied by their 



DUPLICATE NATURE OF THE ALCOHOL-RADICALS. 525 

owii pressure. On breaking the extremity of the tube under water, this 
liquid rapidly escapes in, the form of gas, which proves on examination 
to contain ethene (C 2 H 4 ), ethane (C 2 H 6 ), and di-etltyle (C 2 H 5 ) 2 , the last 
of which may be obtained nearly pure by collecting the last portions of 
gas separately, since it is the least volatile of these hydrocarbons. 

Neglecting the secondary decompositions which give rise to the other 
products, the formation of di-ethyle would be represented by the simple 
equation, 2C 2 H 5 I + Zn = Znl 2 + (C 2 H 5 ) 2 . It is obtained in larger quan- 
tity by heating ethylic iodide with zinc and precipitated copper (page 
14). , 

Di-ethyle or ethyle is a colourless gas, having a faint ethereal smell, 
insoluble in water, and requiring a pressure of two or three atmospheres 
for its liquefaction. The interest which attaches to it is due to its being 
regarded by many chemists as the radical or starting-point of the series of 
compounds derived from vinic alcohol, which is thence spoken of as the 
ethyle series, and this view of the constitution of these compounds was 
in favour long before the compound (C 2 H 5 ) 2 was obtained in the separate 
state, this being a discovery of recent date. 

Mention has already been made of the existence of another radical, 
methyle (CH 3 ) 2 , obtained by a similar process, which may be regarded as 
the starting-point of the wood-spirit series. 

Butyle (C 4 H 9 ) 2 , ample (C 5 H 11 ) 2 , and caproyle (C 6 H 13 ) 2 , the supposed 
radicals of the butylic, amy lie, and caproic alcohols, have also been ob- 
tained, these being liquids with progressive boiling-points. We are thus 
in possession of several members of a homologous series of hydrocarbons, 
which may be designated the alcohol-radicals, and represented by the 
general formula (C n H 2n+1 ) 2 . 

If a mixture of ethyle iodide and amyle iodide (C 5 H n I, prepared 
from fousel oil just as ethyle iodide is from alcohol) be heated with 
sodium, a colourless liquid is obtained, which is a true combination of 
ethyle and amyle (C 2 H 5 .C 5 H n ) — 

C 2 H 5 I + C 5 H n I + Na 2 = 2NaI + C 2 H 5 .C 5 H n (Ethyle-amyle). 

In a similar manner, ethyle-butyle (C 2 H 5 .C 4 H 9 ), methyle-caproyle 
(CH 3 .C 6 H 13 ),butyle-amyle (C 4 H 9 .C 5 H n ), andbutyle-caproyle (C 4 H 9 .C 6 H 13 ), 
have been obtained. 

These double radicals all yield two volumes of vapour for each mole- 
cule of the compound, showing that the empirical formula for methyle 
(CH 3 ), which furnishes only one volume, must be converted into that of 
a double radical, di-methyle (CH 3 .CH 3 ), which would give two volumes 
of vapour, and in a similar manner, ethyle would become (C 2 H 5 ,C 2 H 5 ), 
butyle (C 4 H 9 ,C 4 H 9 ), and so on. 

This duplicate nature of the radicals at once explains the circumstance 
that they do not unite directly with chlorine, bromine, &c, as might have 
been expected. Thus ethyle, with iodine, does not combine to form 
ethyle iodide, because the ethyle itself is an ethylide of ethyle. 

Again, the formation of zinc-ethyle (C 2 H 5 ) 2 Zn, and of ethyle hydride 
or ethane (C 2 H 5 H), during the action of zinc upon ethyle iodide, becomes 
intelligible upon this view. Indeed, the first stage of this action appears 
to consist in the formation of zinc-ethyle — 

2C 2 H 5 I + Zn 2 = (C 2 H 5 ) 2 Zn + Znl 2 . 



526 OXALIC ETHER. 

In the second stage, the zinc-ethyle acts upon a fresh portion of ethyle 
iodide, producing zinc iodide and the double radical ethyle — 

2C 2 H 5 I + (C 2 H 5 ) 2 Zn = Znl 2 + 2(C 2 H 6 .C 2 H 5 ). 

The ethyle hydride itself clearly corresponds to the double radical 
ethyle, one-half of which is replaced by an atom of hydrogen (C 2 H 5 .H). 

The simultaneous formation of ethyle hydride, and of olefiant gas 
during the action of zinc upon ethyle iodide, might be represented by 
the equation — 

2C 2 H 5 I + Zn = Znl 2 + C 2 H 5 .H + C 2 H 4 . 

Ethyle hydride is the representative of a series of homologous hydro- 
carbons, of which the first member, the methyle hydride (CH 3 .H), is 
identical with marsh gas. 

The following table exhibits some of the chief members of the marsh 
gas series of hydrocarbons (or paraffins, general formula C n H 2n+2 ), as 
well as the corresponding alcohol-radicals,* having the general formula 
2(C„H 2 „ +1 )- 

Radical. Hydride, t 

Methyle, . CH 3 .CH 3 CH 3 .H = CH 4 Methane. 

Ethyle, . . G,H 5 .C 2 H 5 C 2 H 5 .H = C 2 H 6 Ethane. 

Butyle, . . C4H 9 .C 4 H 9 C 4 H 9 .H = C 4 H 10 Butane. 

Amyle, . . C 5 H n .C 5 H n C 5 H n .H = C 5 H 12 Pentane. 

The three first of these hydrides are gaseous, the last a volatile liquid. 

If ethyle (C 2 H 5 ) 2 = E 2 be accepted as the radical of the alcohol series, 
then ether (C 2 H 5 ) 2 would become the ethyle oxide, and alcohol (C 2 H 5 HO) 
the ethyle hydrate ; and it will be seen that upon this view a considerable 
number of the relations of these bodies can be readily explained. 

372. On referring to the action of hydrochloric acid upon ether, it will 
be seen to resemble exactly that of the same acid upon the basic oxide of 
a metal, consisting in an exchange between the chlorine of the acid and 
the oxygen of the base. Ethyle chloride may also be produced by the 
action of hydrochloric acid upon alcohol (EHO), just as potassium chloride 
is produced by the action of that acid upon caustic potash — 

EHO {Alcohol) + HC1 - EC1 {Ethyl chloride) + H 2 . 

It would be expected that the action of other acids upon alcohol would 
correspond to their action upon caustic potash, and with several acids this 
is really the case, although it is far more difficult to break up the alcohol 
than the caustic potash. 

If alcohol be boiled for many hours with dry oxalic acid (H 2 C 2 4 ) in 
a flask provided with a long tube, so that the volatilised alcohol may run 
back, it is found that, .on diluting the solution with water, a heavy fra- 
grant liquid separates, which has the composition (C 2 H 5 ) 2 C 2 4 , and is 
termed oxalic ether; 2EHO + H 2 C 2 4 = E 2 C 2 4 + 2H 2 0. 

By treatment with caustic potash, the oxalic ether is decomposed, 
yielding potassium oxalate and alcohol ; thus — 

E 2 C 2 4 + 2KHO == K 2 C 2 4 + 2EHO . 

* See also American petroleum, page 473. 

f Each of these hydrides is isomeric with the radical immediately preceding it. Thus 
ethyle hydride has the same composition as methyle, and is regarded by some chemists 
as identical with it, for when the so-called methyle (or dimethyle) is treated with chlorine, 
it yields ethyle chloride precisely as ethyle hydride does. 



ETHEKS. 527 

But if oxalic ether be mixed with only half the quantity of caustic potash 
required for this decomposition, there is obtained, instead of potassium 
oxalate, a salt, crystallising in pearly scales, having the composition 
KEC 2 4 , the formation of which is easily understood — 

E 2 C 2 4 + KHO = KEC 2 4 + EHO . 

Oxalic ether. Potassium oxalovinate. 

By decomposing this salt with hydrofluosilicic acid (see page 185) to 
remove the potassium in an insoluble form, a new acid is obtained, which 
has the composition HEC 2 4 , and is called oxalouinic or oxalethylic acid, 

Most of the acids form ethers corresponding to oxalic ether ; thus, by 
distilling acetic acid with alcohol and sulphuric acid, and diluting the 
distilled liquid with water, acetic ether (EC 2 H 3 2 ) is separated, remark- 
able for its very fragrant odour, which has a share in the perfume of cider, 
perry, vinegar, and of many wines. 

The ether used in medicine under the names of sweet spirits of nitre, 
nitrous ether, and nitric ether, is essentially a solution of nitrous ether 
(C 2 H 5 )N0 2 in alcohol, and is prepared by distilling alcohol with nitric 
and sulphuric acids and copper wire, when a complex reaction takes place, 
the formation of the nitrous ether being represented by the equation — 

C 2 H 5 .HO + HN0 3 + H 2 S0 4 + Cu = C 2 H 5 .N0 2 + 2H 2 + CuS0 4 . 

Another portion of the alcohol is converted into aldehyde by the oxidising 
action of the nitric acid. 

Nitrous ether is a very volatile liquid, boiling at 62° F., characterised 
by a powerful odour of rennet-apples, and, in the pure state, decomposing 
spontaneously, evolving nitric oxide. 

Nitro-ethane is an acid liquid having the same composition as nitrous ether, and 
obtained by treating ethyle iodide with silver nitrite ; nascent hydrogen converts 
it into ethylamine. When acted on by sodium hydrate dissolved in alcohol, it forms 
an explosive compound C 2 H 4 NaN0 2 . 

True nitric ether (EN0 3 ) may also be obtained as a fragrant, heavy oily liquid, by 
distilling alcohol with nitrie acid, under certain precautions. It is decomposed with 
explosion at a temperature of about 200° F. 

By the action of nascent hydrogen upon nitric ether, a basic substance is produced, 
which has been named hydroxylamine, in allusion to its remarkable formula, lvH 3 0. 
which might be regarded as ammonia, NH 3 , in which one atom of hydrogen is 
replaced by hydroxyle ; C 2 H 5 N0 3 + H 6 = C 2 H 5 HO + H 2 + KTJ 3 0. 

In order to obtain this base, 5 parts of nitric ether are acted on by 12 parts of tin 
and 50 parts of concentrated hydrochloric acid. When the action is over, the alcohol 
is expelled by heat, the tin precipitated by hydrosulphuric acid, the solution evapo- 
rated to dryness, and the residue boiled with absolute alcohol, which leaves some 
ammonium chloride undissolved. The hydroxylamine hydrochlorate (NH 3 O.HCl) 
crystallises in long needles from the alcoholic solution. From the hydroxylamine 
sulphate, by decomposition with baryta, a solution of the base itself may be obtained, 
but pure hydroxylamine has not been isolated from the solution, since it has a ten- 
dency to decompose into ammonia, water, and nitrogen — 

3NH 3 = NH 3 + N 2 + 3H 2 0. 

Hydroxyurea, CH 3 (HO)N 2 0, or urea in which hydrogen is replaced by hydroxyle, 
has also been obtained. 

The chloric ether used for medicinal purposes is not an ether in the true sense of 
the term, but a solution of chloroform (CHC1 3 ) in alcohol. Chloroform will be more 
particularly described hereafter. 

Perchloric ether, (C 2 H 5 )C10 4 , is only interesting from the circumstance that, 
although an oily liquid, it explodes violently under a sudden blow. 

Boracic ether, which has the formula E 3 B0 3 , is formed when boron trichloride is 
decomposed by alcohol; BC1 3 + 3(EH0) = E 3 B0 3 + 3HC1, and may also be obtained 
by heating boracic anhydride with an excess of alcohol under pressure. It is lighter 



528 sulphovinic: acid. 

than water (sp. gr. 0*88), and boils at 246° F. When heated with boracic anhydride 
it is converted into E 2 0. B 2 3 , which is decomposed by heat into E 3 B0 3 and E 2 0.3B 2 3 , 
the latter being a vitreous solid. 

When silicon tetrachloride is decomposed by alcohol, the compound 2E 2 O.Si0 2 is 
produced; SiCl 4 + 4(EHO) = 2E 2 O.Si0 2 (Silicic ether) + 4HC1. This silicic ether is 
a colourless liquid, of sp. gr. 0*93, and distilling unchanged at 330° F. It has an 
ethereal odour, and burns with a brilliant flame which deposits silica. When poured 
upon the surface of water, it gradually decomposes, with separation of gelatinous 
hydrated silica ; 2E 2 0. Si0 2 + 2H 2 = 4(EHO) (Alcohol) + Si0 2 . 

When the ether is kept in a moist atmosphere, it deposits a hard transparent mass 
of silica, known as artificial quartz. 

Two other silicic ethers have been obtained, having respectively the composition 
E 2 O.Si0. 2 and E 2 0.2Si0 2 ; the former liquid, the latter viscous. 

Carbonic ether (E 2 C0 3 ) may be obtained by heating silver carbonate with ethyle 
iodide in a sealed tube ; Ag 2 C0 3 + 2EI = E 2 C0 3 + 2AgI. 

The compound 2E 2 O.C0 2 or C(OE) 4 has been obtained by the action of sodium 
upon an alcoholic solution of chloropicrine — 

CC1 3 (N0 2 ) + 4(EHO) + Na 4 = 3NaCl + NaN0 2 + j ^OOcT i + B *' 
Chloropicrine. Alcohol. Ethyle ortho-carbonate. 

When carbonic acid gas is passed through a solution of potassium hydrate in 
absolute alcohol, the potassium carbovinate is obtained in crystals having the com- 
position KEC0 3 , corresponding to KHC0 3 . 

By the action of syrupy phosphoric acid upon alcohol, the compound H 2 EP0 4 , 
phosphethylic acid, is formed, and by neutralising it with a base, a phosphethylate 
may be obtained, composed after the general formula M' 2 EP0 4 . A second acid is 
formed at the same time, having the formula HE 2 P0 4 , its salts being M'E 2 P0 4 . The 
true phosphoric ether E 3 P0 4 is also said to have been obtained. 

The true sulphuric ether (E 2 S0 4 ) may be formed by passing the vapour of anhy- 
drous sulphuric acid into ether, or by decomposing ethyle iodide with silver sulphate. 
It is an oily liquid heavier than water, and decomposed by heat, defiant gas and 
alcohol being found amongst the products. 

The fragrant liquid known as heavy oil of wine, which is formed towards the latter 
part of the preparation of ether and of defiant gas, has been found by Hartiug to 
contain ethyl-amyle ether (C 2 H 5 .C 5 H n .O), ethyl-amyle ketone (C 2 H 5 .C 5 H n .CO), and 
methyl hexyle ketone (CH 3 .C 6 H 12 .CO). 

373. When ether or alcohol is added to concentrated sulphuric acid, 
much heat is evolved, in consequence of the formation of sidphovinic or 
sidphethylic acid, HES0 4 , corresponding in composition to KHS0 4 . If 
baryta be now added to the solution, the uncombined sulphuric acid will 
be precipitated in the form of barium sulphate, but the sulphovinic acid will 
form the barium sulphovinate, which may be obtained by evaporating the 
solution, in rhombic prisms which have the formula BaE 2 (S0 4 ) 2 2Aq., and 
are easily soluble in water. By cautiously adding sulphuric acid to the 
solution of barium sulphovinate till the whole of the barium is precipitated- 
as sulphate, and evaporating the filtered liquid in vacuo, the pure sul- 
phovinic acid is obtained as a syrupy liquid liable to- spontaneous decom- 
position, and readily decomposed, when heated with water, into alcohol 
and sulphuric acid — 

HES0 4 + H 2 = H 2 S0 4 + EHO. 

Sulphovinic acid. Alcohol. 

The sodium sulphovinate, prepared by decomposing the barium salt 
with sodium carbonate, is used, medicinally in Germany. 

374. Vinic acids are not formed by monobasic acids. — It must be 
noticed that although the greater number of the acids are capable of 
forming ethers, only a few of them produce vinic acids. Indeed, only 
those acids form vinic acids which are polybasic,. .i.e., require more than 



THEORY OF FORMATION OF ETHER. 529 

one atom of a metal for the formation of a normal salt (page 250), the 
tendency to form a vinic acid depending upon the possibility of replacing 
a portion of the hydrogen in the acid by ethyl e. In the case of nitric 
acid, which is undoubtedly a monobasic acid, and does not form acid 
salts, no vinic acid can be produced ; the formula of the acid being 
HIS r 3 , the hydrogen must be entirely or not at all replaced by the 
ethyle. 

375. Theory of etherification. — When sulphovinic (or sulphethylic) 
acid is decomposed by heat, especially in the presence of excess of alcohol, 
a large proportion of ether is found among the products, and this lias 
given rise to a very general opinion among chemists, that the production 
of sulphovinic acid is an intermediate stage in the formation of ether, by 
the ordinary process of distilling alcohol with sulphuric acid. At first 
sight it would appear that the etherification of alcohol in this process was 
sufficiently explained by reference to the attraction of sulphuric acid for 
water, and consisted in a simple removal of water from the alcohol by the 
acid, for 2C 9 H 6 - H 2 = C 4 H 10 O. 

Alcohol. Ether. 

"When it is found, however, that a continuous stream of alcohol, flowing 
into heated sulphuric acid in a retort, is converted into ether and water, 
which is not retained by the sulphuric acid, but distils over with the 
ether, and that this may go on almost without limit, this explanation is 
no longer tenable. 

Accordingly, the formation of ether from alcohol by the action of sul- 
phuric acid is generally referred to the formation of sulphovinic acid, as 
soon as the alcohol and the acid are brought in contact, and the subse- 
quent decomposition of this sulphovinic acid, in the presence of alcohol, 
into sulphuric acid, water, and ether ; thus — 

HES0 4 + EHO = H 2 S0 4 + E 2 . 

Sulphovinic acid. Alcohol. Ether. 

The sulphuric acid thus set free would of course give rise to the forma- 
tion of a fresh quantity of sulphovinic acid, which would be decomposed 
in its turn, and so on without limit. 

A strong argument in favour of this view is deducible from the follow- 
ing experiment : — 

When amylic alcohol (the amylic hydrate C 5 H n HO) is mixed with 
concentrated sulphuric acid, it forms sulphamylic acid (C 5 H n )HS0 4 , 
corresponding to sulphovinic acid, and if this be heated in a retort, and 
alcohol be allowed to flow into it as in making ether, the first portion which 
distils over is found to be a true double ether molecule (C 2 H 5 .C 5 H n .O), the 
production of which would be represented by the equation — 

H(C 5 H ll )S0 4 + C 2 H 5 HO = C 2 H 5 .C 5 H lr O + H 2 S0 4 . 

Sulphamylic acid. Alcohol. Amylethylic ether. 

On continuing the distillation, nothing but ordinary ethylic ether is 
obtained. 

The existence of these double ethers might have been anticipated from 
what has been said with respect to the double radicals (page 525), but 
the mode of formation in the above instance certainly affords support to 
the view, that ether results from the decomposition of sulphovinic acid 
by alcohol in the ordinary etherifying process. 

2L 



530 CONSTITUTION OF ALCOHOL AND ETHER. 

On the other hand, this theory of etherification is shaken by the circum- 
stance, that if vapour of alcohol be passed into boiling sulphuric acid of 
sp. gr. 1*52 (boiling at 290° F.) almost the whole of the alcohol is resolved 
into water and ether, which distil over, so that either no sulphovinic acid 
is formed, or it is only formed to be immediately decomposed. If the 
acid have the sp. gr. 1*61 (boiling at 330° F.), no ether is obtained, the 
alcohol being resolved into olefiant gas and water. 

Moreover, hydrated phosphoric acid cannot be substituted for the 
sulphuric acid in the preparation of ether, notwithstanding that it also 
forms a vinic acid. 

Hence, many chemists are inclined to attribute to sulphuric acid a 
specific action by contact {catalytic action) upon alcohol, causing its 
resolution into water and ether, or olefiant gas, according to the tem- 
perature. This view receives some confirmation from the behaviour of 
sulphuric acid towards cellulose and certain other substances, in which it 
causes important transformations, without itself appearing to take part in 
the change. 

In connexion with this subject, it is remarkably interesting to observe, 
that alcohol may actually be reproduced from olefiant gas and water 
under the influence of sulphuric acid. If concentrated sulphuric acid be 
violently agitated in a vessel containing olefiant gas, the latter is absorbed, 
and on diluting the acid with water and distilling, a quantity of alcohol 
is obtained. 

376. Alcohols and ethers referred to the ivater-type. — When potassium 
or sodium is thrown into absolute alcohol, the metal is dissolved with 
disengagement of heat and rapid evolution of hydrogen, and a crystalline 
compound is formed, known as potassium ethylate or sodium ethy late, and 
containing an atom of the metal in the place of an atom of hydrogen ; the 
action of potassium upon alcohol would be thus represented — 

C 2 H 5 HO (Alcohol) + K = C 2 H 5 KO (Potassium ethylate) + H . 

Other alcohols behave in a similar manner. No one can fail to be struck 
with the similarity which exists between the action of potassium upon 
alcohol and upon water, and chemists have naturally endeavoured to refer • 
both actions to a common type. 

The decomposition of water by potassium is represented by the 
equation — 

Alcohol may be represented with equal fitness, as water in which half 
the hydrogen is replaced by ethyle (C 2 H 5 ), or EHO, and the action of 
potassium upon it may be thus expressed — 

EJ + K=|}0 + H. 

In a similar manner sodium ethylate would be formed. 

This substance has been found useful in surgery as a caustic antiseptic, 
since it is decomposed by water, when applied to a wound, yielding 
caustic soda and alcohol, to which the antiseptic action is due. 

Aluminium does not act upon alcohol, but if a little iodine be dis- 
solved in the alcohol, and the solution heated with aluminium, hydrogen 
is evolved and aluminium ethylate, A1 2 (C 2 H 5 0) 6 , is produced. Probably 



MERCAPTAN. 531 

the aluminium iodide first produced decomposes with the alcohol, forming 
aluminium ethylate and hydric iodide ; the latter, being acted on by the 
excess of aluminium, evolves hydrogen and forms more aluminium iodide, 
which decomposes a fresh portion of alcohol, and thus a small quantity 
of iodine carries on a Continuous action. Other aluminium alcohols are 
produced in a similar manner. 

Thallium-ethylate, C 2 H 5 T10, has also been obtained as a colourless liquid remark- 
able for its high specific gravity (3 "55) and great refractive and dispersive action upon 
light. Barium-ethylate, (C 2 H 5 0) 2 Ba, is obtained by the action of anhydrous baryta 
on absolute alcohol. A trace of water precipitates barium-hydrate from the solution. 
On heating the alcoholic solution, the barium-ethylate precipitates, being less soluble 
in hot alcohol. The alcoholic solution absorbs carbonic oxide at the ordinary 
temperature, yielding a salt isomeric with barium propionate; (C.,H 5 0) 2 Ba + 2CO 
= Ba(C 3 H 5 2 ) 2 . 

When sodium ethylate is heated in a sealed tube with the iodide of 
one of the alcohol-radicals, the sodium combines with the iodine, whilst 
the alcohol-radical enters into the place of the sodium, and a double 
ether is formed. 

Thus, if methyle iodide. (CH 3 I) be decomposed by sodium ethylate — 

CH 3 I + ivr, f (Sodium-ethylate) = ^Nal + nxx r {Methyl-ethylic ether). 
In a similar manner amyl-ethylic ether, ^ -X > 0, would be produced. 

Again, if ethyle iodide be decomposed by sodium-alcohol, common 
ether is obtained, and the action must in consistency be similarly ex- 
plained- 

;2 H 5 I 
'2^-5 I 



ftl + C ^l0 .. Nal + 



377. Compounds have been obtained corresponding to alcohol and ether, in which 
the place of the oxygen is occupied by sulphur, and which bear the same relation to 
hydrosulphuric acid as alcohol and ether bear to water. 

XT 

Type — Hydrosulphuric acid, „ 

Hydrosulphuric ether, C 9 H= ) x> , , ,. -, K 

(ethyle sulphide); cJhI \ S Potassi ™ sulphide, 

OH) 

Mercaptan, . . 2 tt 5 [ S Potassium hydrosulphate, y r S . 

These compounds are distinguished for their powerful odour of garlic. This is 
especially the case with mercaptan, whioh is notoriously one of the most evil-smelling 
chemical compounds. It is prepared by distilling solution of potassium hydrosul- 
phate (obtained by saturating potash with hydrosulphuric acid) with sulphovinate of 
potassium, or better, of calcium— 

KC 2 H 5 S0 4 , + § J S =-. C ^ J S + K 2 S0 4 . 

Potassium Mercaptan. 

sulphovinate. 

Mercaptan is a light, very volatile and inflammable liquid, sparingly soluble in 

water. That it is constituted after the type of hydrosulphuric acid is shown by its 

action upon metals and their oxides. Potassium acts upon it precisely as it does upon 

alcohol — 

C H ) f ' H ) 

' 2 tt° t S (Mercaptan) + K = S y 5 > S (Potassium-mercaptan)' + H . 

Its name was bestowed in allusion to its action upon mercuric oxide, when it 
forms a white crystalline inodorous compound, insoluble in water, but soluble in 
alcohol — 

2(C. 2 H 5 )HS + Hg"0 = (C 2 H s ) 2 S.Hg"S + H 2 . 
Mercaptan. Mercaptide of mercury. 



532 ARSENICAL ALCOHOL OR ALCARSIN. 

378. Hydrocyanic ether (C 2 H 5 .CN = ECy), or ethyle cyanide, is obtained by heat- 
ing ethyle iodide with silver cyanide ; C 2 H 5 I + AgCN" = C 2 H g .CN + Agl. 
Ethyle cyanide is a volatile poisonous liquid, smelling strongly of garlic. 



KAKODYLE SEKIES— ORGANO-METALLIC BODIES. 

379. One of the most pleasing results of the progress of investigation 
in chemistry is the discovery of the true position among classified com- 
pounds which is to be assigned to some substance hitherto regarded as 
anomalous, and as destroying by its presence the symmetry and complete- 
ness of an otherwise perfect classification. Such was the case, until 
within the last few years, with kakodyle, and the bodies derived from it. 
Discovered long before the science of organic chemistry was prepared to 
receive it, it taxed the ingenuity of chemists to find a place for it in their 
arrangement of organic compounds, and always occupied an anomalous 
and isolated position. Modern research has now brought to light a whole 
series of compounds, which would not have been complete without kako- 
dyle, and this hitherto incomprehensible substance has at length been 
assigned its proper place. 

When a mixture of equal weights of white arsenic and dry potassium 
acetate is submitted to distillation, a heavy poisonous liquid is obtained, 
which has a most disgusting odour of garlic, and takes fire spontaneously 
when exposed to the air. This liquid, which has long been known under 
the names of alcarsin (arsenical alcohol) and Cadet's fuming liquor, has 
the composition C 4 H 12 As 2 0, and its production may be represented (if the 
various secondary products be neglected) by the equation — 

4KC 2 H 3 2 + As 2 3 = C 4 H 12 As 2 + 2K 2 C0 3 + 2C0 2 . 

Potassium acetate. Alcarsin. 

The spontaneous combustibility of the crude product is due to the presence of 
kakodyle. 

If acetic acid be represented as derived from formic acid by the substitution of 
methyle for hydrogen, the formation of alcarsin would be easily explained. Potassium 

acetate would then be represented by the formula prr [ C0 2 , and its action upon 

arsenious anhydride might be thus expressed — 

A^O | ° + 4 CH 3 1 C0 * = A$H& | ° + 2K * C0 « + 2C0 =- 

Alcarsin. 

Alcarsin has the properties of a base ; it is capable of combining with 
the oxygen acids to form crystalline salts, and in contact with the hydro- 
gen acids it furnishes water, together with a salt of the radical of the acid. 
Thus, with hydrochloric acid, we have — 

C 4 H 12 As 2 + 2HC1 = 2As(CH 3 ) 2 Cl + H 2 . 

Alcarsin. Kakodyle chloride. 

The best method of obtaining this chloride consists in dissolving the 
alcarsin in alcohol, and adding an alcoholic solution of corrosive sublimate, 
when a white crystalline solid is obtained, composed of C 4 H 12 As 2 O.HgCl 2 ; 
and on distilling this with hydrochloric acid (out of contact with air), a 
spontaneously inflammable liquid is obtained, of insupportable odour, and 
composed of C 2 rI 6 AsCl. By distilling this chloride with zinc in an atmo- 
sphere of carbonic acid gas, a third unbearable liquid is procured, which 
has the formula C 4 H 12 As 2 , and has been named kakodyle, in allusion to 



KAKODYLE SERIES. 533 

its intolerable odour (ko.ko9, bad). This substance is obviously the radical 
from which the compounds just mentioned are immediately derived ; 
thus — 

Kakodyle, C- 4 H 12 As 2 = Kd 2 

Alcarsin, or kakodyle oxide, C 4 H 12 As 9 = Kd 2 
Kakodyle chloride, C 2 H 6 AsCl = KdCl . 

The remarkable properties of kakodyle leave no doubt as to its being 
really the radical of these compounds, in the same sense in which potas- 
sium is the radical of the oxide and chloride of that metal, for kakodyle 
enters into direct combination with chlorine and with oxygen, its attrac- 
tion for the latter being so energetic as to cause its spontaneous inflamma- 
tion in the air. 

The discovery of this radical, comporting itself in all respects like a 
metal, was of the utmost importance in its effect upon organic chemistry, 
affording very strong ground for belief in the existence of other quasi- 
metallic radicals, such as ethyle, methyle, &c, which have only recently 
been isolated. A similar service had been previously rendered to the 
science by the discovery of the compound radical cyanogen (CIST) belong- 
ing to the electro-negative class opposed to the metals, and for a long time 
these two remained the only compound radicals which had been obtained 
in a separate form. 

When kakodyle is brought gradually in contact with oxygen, it is first 
converted into kakodyle oxide ((C 2 H 6 As) 2 0), and subsequently, if water 
be present, into kakodylic acid (HC 2 H 6 As0 2 = HKd0 2 ), which forms pris- 
matic crystals, unaltered by air, and destitute of poisonous character. 
When treated with hydrochloric or hydrosulphuric acid, it yields trichloride 
(KdCl 3 ) and sesquisidphide of kakodyle (Kd 2 S 3 ).- 

The most poisonous member of this series is kakodyle cyanide 
(C 2 H 6 As.CN" = KdCy), which is easily obtained in crystals by decompos- 
ing mercuric cyanide in solution with kakodyle oxide — 

HgCy 2 + Kd 2 = HgO + 2KdCy. 

A very minute quantity of this substance diffused in vapour through the 
air has the most dangerous effect upon those inhaling it. 

The following are the most important members of the kakodyle series : — 



Kakodyle, 


(C 2 H 6 As) 9 =Kd 9 


Kakodyle oxide, 


(CoH 6 As)^0 = Kcl>0 


,, sulphate, 


(CoH 6 As)oO.S0 3 = Kd o .S0 4 


,, sulphide, 


(C 2 H fi As)oS = Kd 9 S 


,, chloride, 


C.,H fi AsCl=KdCl 


Kakodylic acid, 


HC 2 H 6 As0 2 =HKd0 2 


Silver kakodylate, 


AgC„H 6 AsOo = AgKd0 9 


Kakodyle sesquisulphide, 


(C 2 H 6 As) 2 S 3 =Kd 2 S 3 


,, trichloride, 


CoH 6 AsCl 3 =KdCl 3 



380. Organo-metcdlic compounds. — The only way of referring kakodyle 
to any known series was to regard it as an association of arsenic with 2 
atoms of methyle (CH 3 ), and this supposition necessitated the existence 
of other compounds of a similar nature, formed, that is, by the association 
of an inorganic element with a quasi-metallic radical. Accordingly, 
within the last few years, it has been discovered that by heating the 
iodides of methyle, ethyle, and amyle with zinc, compounds of those 
radicals with the metal can be obtained, and these compounds, like kako- 
dyle, are distinguished by their remarkable attraction for oxygen. 



534 



PREPARATION OF ZINC-ETHYLE. 



Nor are arsenic and zinc the only elements with which these radicals can 
be associated; boron, potassium, sodium, magnesium, aluminium, cadmium, 
tin, antimony, bismuth, lead, and mercury may be made to furnish similar 
compounds, and the principle is now fully established that the alcohol- 
radicals can enter into combination with metals to form compounds which 
are, in some cases, capable of direct union with oxygen and other electro- 
negative elements, for which they exhibit a greater attraction than the 
metals themselves. 

The members of this class of organo-metallic bodies which have been 
the subjects of some of the most important researches deserve special 
attention. 

Zinc-ethyle is prepared by the action of zinc upon ethyle iodide — 

2C 2 H 5 I + Zn 2 = (C 2 H 5 ) 2 Zn + Znl 2 . 

Eight hundred grains of bright freshly granulated and thoroughly dried zinc are 
placed in a half-pint flask (E, tig. 290), which is connected with the carbonic acid 
apparatus (A), from which the gas is passed through strong sulphuric acid in the 
bottles (B and C) where it is thoroughly dried. A second perforation in the cork of 
the flask (E) allows the passage of the tube/, which passes through the two corks in 
the wide tube F, and dips into a little mercury in D. A stream of cold water is 
kept running through the wide tube (F), being conveyed by the caoutchouc tubes t 1. 
When the whole apparatus has been filled with carbonate acid gas the cork of the 




Fig. 290. — Preparation of zinc-ethyle. 

flask (E) is removed, and 400 grains of ethyle iodide (perfectly free from moisture) are 
introduced, the cork being then replaced.* The carbonic acid gas is again passed 
for a short time, and then cut off by closing the nipper-tap (T) upon a caoutchouc 
connector, when the gas escapes through the tube (G), which dips into mercury. A 
gentle heat is then applied by a water-bath to the flask (E) till the ethyle iodide boils 
briskly, the vapour being condensed in the tube /, and running back into the flask. 
In about five hours the conversion is complete, and the iodide ceases to distil. The 
nipper-tap (T) is agaiu opened, and a slow current of carbonic acid gas is allowed to 
pass; the position of the condenser (F) is reversed (fig. 291), and the tube/ is con- 
nected by the cork K, with the short test-tube ; the longer limb of a very narrow 
siphon (I) of stout tube passes through a second perforation in the cork (K), "the 
shorter limb passing into the- very short test-tube (P), the cork of which is also 
furnished with the short piece of moderately wide tube (L). For receiving and pre- 
serving the zinc-ethyle, a number of small tubes are prepared of the form shown in 

* The process is said to be much accelerated if about z l s of zinc-ethyle is dissolved in the 
ethyle iodide. 



ZINC-ETHYLE. 535 

g. 292. The long narrow neck (E) of one of these is passed down the short tube (L) 
to the bottom of P, the other end (N) of the tube being connected with an apparatus 
for passing dry carbonic acid gas. The whole of the apparatus being filled with this 
gas, the nipper-tap is closed, and the flask (E) heated on a sand-bath, so that the zinc- 
ethyle may distil over, a slow stream of carbonic acid gas being constantly passed 
into P, the excess escaping through L. When enough zinc-ethyle has collected in 
the tube (0) a blowpipe flame is applied to the narrow tube (N), which is drawn off 




Fig. 291. — Collection of zinc ethyie. 

and sealed ; the siphon tube (I) is then gradually pushed down, so that its longer 
limb may be sufficiently mmersed in the zinc-ethyle, and the nipper-tap (T, fig. 290) 
is opened, when the pressure of 




the carbonic acid gas forces over 

a part of the zinc-ethyle into the 

tube P. By heating the tube (M) 

with a spirit-lamp, so as to expel 

part of the gas, allowing it to Fig. 2*»2. 

cool, it will become partly filled 

with zinc-ethyle, and may be withdrawn and quickly sealed by the blowpipe. The 

spontaneous inflammability of the zinc-ethyle, and its easy decomposition by water, 

render great care necessary in its preparation. If an alloy of zinc with one-fourth its 

weight of sodium be employed, the conversion may be effected in an hour. 

If any moisture were present in the materials employed, it would 
decompose a corresponding quantity of the zinc-ethyle, yielding zinc oxide 
and gaseous ethyle hydride — 

(C 2 H 5 ) 2 Zn + H 2 = 2(C 2 H 5 .H) + ZnO . 

Zinc-ethyle is a colourless liquid of powerful odour, heavier than water 
(sp. gr. 1*18), and boiling at 244° F. In contact with atmospheric air, 
it takes fire spontaneously, burning with a dazzling greenish-blue name 
which emits white clouds of zinc oxide. If a piece of porcelain be 
depressed upon the name, a deposit of metallic zinc is formed, surrounded 
by a ring of oxide, which is yellow while hot, and white on cooling. 

When oxygen is allowed to act very gradually upon zinc-ethyle, zinc 
ethylate is formed, corresponding to potassium and sodium ethylates, 
which have been already described j (C 2 H 5 ) 2 Zn + 2 = Zn(C 2 H 5 ) 2 2 . 

Under the gradual action of other electro-negative elements, zinc-ethyle 
is decomposed into compounds of zinc and ethyle with the particular 
element employed ; (C 2 H 5 ) 2 Zn + 1 4 = 2C 2 H 5 I + Znl 2 . 

Zinc-methyle (CH 3 ) 2 Zn is prepared by the action of zinc upon the 
methyle iodide (CH 3 I), and resembles zinc-ethyle in its general character ; 
it is, however, far more volatile and more energetic in its reactions than 
zinc-ethyle, and is decomposed with inflammation and explosion when 



536 ARSENAIO-TRIETH YLE. 

brought in contact with water, yielding zinc oxide and marsh gas (methyle 
hydride) ; (CH 3 ) 2 Zn + H 2 = 2(CH 3 .H) + ZnO. 

Zinc-amyle (C 5 H 11 ) 2 Zn is not so violent in its reactions; it does not 
inflame when exposed to air, but absorbs oxygen very rapidly. 

Potassium-ethyle and sodium-ethyle (C 2 H 5 .K and C 2 H 5 .IN T a) have as 
yet been obtained only in combination with zinc-ethyle, by heating this 
liquid in a sealed tube with potassium or sodium, when metallic zinc is 
separated, and the alkali-metal takes its place — 

3(C 2 H 5 ) 2 Zn + Na 2 = 2(Zn(C 2 H 5 ) 2 .NaC 2 H 5 ) + Zn. 

The double compound of sodium-ethyle with zinc-ethyle is a crystalline 
solid which decomposes water with great violence, forming soda, zinc 
oxide, and ethyle hydride.* Its behaviour with carbonic acid gas is very 
interesting and important. 

When the crystalline compound of sodium-ethyle with zinc-ethyle is 
introduced into a bulb tube through which dry carbonic acid gas is 
passed, much heat is evolved, zinc-ethyle distils off, and a white solid is 
left in the bulb, which is found to consist of the sodium propylate 
NaC 3 H 5 2 formed according to the equation — 

C 2 H 5 ¥a + C0 2 = NaC 3 H 5 2 . 

This reaction is one of very great importance, representing the first 
successful attempt to produce directly one of the organic acids from 
carbon dioxide, and indicating a general method for the formation of the 
other acids of the same series. 

Thus, if sodium-methyle be treated in the same way, it yields sodium 
acetate ; CH 3 Na + C0 2 = NaC 2 H 3 2 . 

By heating methyle iodide in a sealed tube with a compound of 
arsenic and sodium, kakodyle or arsenio-dimethyle is obtained — 

2CH 3 I + AsNa 2 = As(CH 3 ) 2 + 2NaI, 

and thus kakodyle finds its place among the organo-metallic bodies, the 
existence of which it foreshadowed. 

When ethyle iodide is treated in a similar manner, arsenio-diethyle, 
As(C 2 H 5 ) 2 , or ethylic-kakodyle, is obtained. 

381. Arsenio-trimethyle or trimethylarsine, As(CH 3 ) 3 , and arsenio- 
triethyle or triethylarsine, As(C 2 H 5 ) 3 , may be obtained by acting upon 
the iodides of methyle and ethyle with a compound of arsenic with 
3 atoms of sodium — 

3CH 3 I + AsNa 3 = As(CH 3 ) 3 + 3]S T aI; 

or by decomposing zinc-methyle or zinc-ethyle with arsenic chloride; 
3Zn(C 2 H B ) 2 + 2 AsCl 3 = 2 As(C 2 H 5 ) 3 + 3ZnCl 2 . 

Arsenio-triethyle has a kakodylic odour, but does not take fire when 
exposed to air, although it oxidises with great rapidity. Like kakodyle, it 
is capable of producing a base by combination with oxygen, which has 
the formula As(C 2 H 5 ) 3 0, and is called arsenic triethoxide. Similar com- 
pounds have been obtained in which the oxygen is replaced by chlorine, 
iodine, and sulphur. 

Other arsenical compounds of ethyle and methyle have been produced 

* Strange to say, when this compound of sodium-ethyle with zinc-ethyle is heated, it 
leaves metallic sodium and zinc. 



ALUMINIUM ETHIDE — TPJBORETHYLE. 537 

containing four atoms of the alcohol-radical, but the oxide of tetrethyl- 
arsonium [As(C 2 H 5 ) 4 ] 2 and its congeners are really substances belonging 
to the ammonium family, and they will be again alluded to elsewhere. 

Stibethyle, Sb(C 2 H 5 ) 3 , or stibiotriethyle, and stibiotriniethyle, Sb(CH 3 ) 3 , 
are obtained by processes similar to those which furnish the corresponding 
compounds of arsenic, which they much resemble. 

Stibethyle has a powerful odour of onions, and takes fire spontaneously 
in air. It combines with oxygen, chlorine, iodine, and sulphur with great 
energy. So powerful is its attraction for chlorine, that it displaces hydrogen 
from concentrated hydrochloric acid — 

Sb(C 2 H 5 ) 3 + 2HC1 = Sb(C 2 H 5 ) 3 . Cl 2 (Stibethyle dichloride) + H 2 . 

Stibethyle oxide is a basic substance. The iodide of tetrethylstibonium, 
Sb(C 2 H 5 ) 4 I, belongs to the ammonium family. 

Mercuric methide Hg(CH 3 ) 2 and ethide Hg(C 2 H 5 ) 2 are formed by the 
action of zinc-methyle and zinc-ethyle upon mercuric chloride — 

Zn(C 2 H 5 ) 2 + HgCl 2 = ZnCl 2 + Hg(C 2 H 5 ) 2 . 

The methyle compouud is the heaviest liquid (except metallic mercury) 
which is known; its specific gravity is 3*07, so that glass floats upon its 
surface. 

Aluminium ethide, A1 2 (C 2 H 5 ) 6 , is obtained by decomposing mercuric 
ethide with aluminium, 3HgE 2 + Al 2 = Hg 2 + A1 2 E 6 . It is a colourless 
liquid, spontaneously inflammable, and decomposed by water. The 
corresponding methyle compound, A1 2 (CH 3 ) 6 , solidifies at a little above 
32° F. into a transparent crystalline mass. 

Triborethyle, B(C 2 H 5 ) 3 , has been obtained by the action of zinc-ethyle 
upon boracic ether — 

2E 3 B0 3 + 3ZnE 2 = 2BE 3 + 3ZnE 2 2 

Boracic ether. Zinc-etlnle. Tribor-ethyle. Etliylate of zinc. 

It distils over as a very light (sp. gr. 0'69) colourless liquid, which has 
an irritating odour, and is insoluble in water. It inflames spontaneously 
in air, burning with a beautiful green flame, and explodes when brought 
in contact with pure oxygen. By gradual oxidation it is converted into 
the compound BE 3 2 , which may be distilled in vacuo without decom- 
position. When this liquid is mixed with water it is decomposed, yield- 
ing alcohol, and a volatile white crystalliue body, BH 2 E0 2 — 

BE 3 2 + 2H 2 - BH 2 E0 2 + 2(EHO). 

This substance has an agreeable odour, and a most intensely sweet 
taste ; it is very soluble in water, alcohol, and ether. 

Boric methide, B(CH 3 ) 3 , is formed by the action of a strong ethereal 
solution of zinc-methyle upon boracic ether — 

2E 3 B0 3 + 3ZnMe 2 = 2BMe 3 + 3ZnE 2 0, 

Boracic ether. Zinc-methyle. Boric methyde. Zinc etliylate. 

Boric methide is a heavy (sp. gr. 1*93) colourless gas, having an intoler- 
ably pungent tear-exciting odour, and capable of liquefaction under a 
pressure of three atmospheres at 50° F. When it issues very slowly into 
the air from a tube, it undergoes partial oxidation, and produces a lam- 
bent blue flame, invisible in daylight, and incapable of burning the 
fingers ; but when it comes rapidly into contact with air, it burns with a 
bright green hot flame, remarkable for the immense quantity of large 



538 



BORIC METHIDE— SILICIUM-ETHYLE. 



flakes of carbon which it disperses through the air, apparently because 
the B 2 3 produced envelopes them and prevents their combustion. 
Eoric methide combines with an equal volume of ammonia gas, producing 
a white, volatile compound NH 3 .BMe 3 , which is deposited in fine crystals 
from its ethereal solution, and may be sublimed without decomposition. 
Its vapour, like that of sal-ammoniac, occupies four volnmes instead of 
two. Water absorbs very little boric methide, but alcohol dissolves it 
readily. Solutions of the alkalies and alkaline earths also absorb it, and 
potash decomposes the ammonia compound, but the combinations of boric 
methide with the alkalies do not crystallise, and are decomposed even by 
carbonic acid gas. 

Silicium-ethyle, SiE 4 , results from the decomposition of silicon tetra- 
chloride with zinc-ethyle; it is not decomposed by water or by solution of 
potash, is lighter than water, and burns with a bright flame. Silicium- 
ethyle is especially interesting as the source of a new alcohol in which a 
part of the carbon appears to be replaced by silicon. The formula of this 
alcohol is said to be SiC 8 H, O, which may be represented as the (missing, 
see page 518) alcohol C 9 H. 20 O (nonyle-alcohol), in which an atom of carbon 
is replaced by an atom of silicon. 

Silicium-hexethyle, Si 2 E 6 , corresponding in composition to aluminium 
ethide, is also an inflammable liquid, the vapour of which has the high 
specific gravity 7*96. 

Silicium-methyle, Si(CH 3 ) 4 , is obtained by the action of SiCl 4 upon 
methyle iodide in the presence of zinc. It is a liquid which burns with 
a luminous flame, producing white fumes of silica. 

382. The following table exhibits the composition of the principal com- 
pounds of alcohol-radicals with inorganic elements which have yet been 
analysed, omitting some of the compound ammonias, which will be noticed 
hereafter : — 



Compounds of alcohol-radicals 


Form ul el 


Inorganic 


with inorganic elements. 




Type. 


Sodium-ethyle, .... 


NaE 


NaCl 


Magnesiivm-ethyle, 






MgE, 


MgCl 2 


Aluminium-ethyle, 






ale; 


A1 2 C1 6 


Zinc- methyle, 






ZnMe 2 


ZnCl 2 


Zinc-ethyle, . 






ZnE 2 ~ 


ZnClo 


Zinc-amyle, . 






ZnAyl 2 


ZnCU 


Stan-methyle, 






SnMe 


SnCl 2 


Stan-ethyle, . 






SnE 2 


SnCi; 


Sesquiethide of tin, 






Sn 2 E 6 


Sn 2 3 


Diethiodide of tin, 






Sn,E 4 I 


Sn 0, 


Stannic ethide, 






SnE 4 


SnCl 4 


Stannic ethjdom ethide, . 






SiiE.,Me.,* 


SnCl 4 


Stannic iodethicle, 






SnE 2 I 2 " 


SnCl 4 


Bismuthous ethide, 






BiE 3 " 


BiCl 3 


Bismnthous dichlorethide, 






BiECU 


BiCl 3 


Plumbic ethide, 






PbE, 


Pb0 2 


Mercuric ethide, . . . 






Hg,E 


HgCl 2 


Mercuric methide, 






HgMe 2 


HgCl 2 


Stibethyle, . . • . 






SbE 3 


SbCl 3 


Antimonic triethoxide, . 






SbE 3 


SbCl 5 



* Formed by the action of zinc-methyle upon the stannic iodethide, ZnMe 2 + SnEo 
= SnEoMeo + Znl 2 . 



CONSTITUTION OF ORGANO-METALLIC BODIES. 



539 



Compounds of alcohol-radicals 


Form ul ji 


Inorganic 


with inorganic elements. 




Type. 


Iodide of tetrethyl-stibonium, 


SbE 4 I 


SbCl 5 


Kakodyle, ..... 


AsMe 2 


As 2 S, 


Kakodyle oxide, .... 


As 2 Me 4 


As 9 3 


Arsenious oxymethide, . 


AsMeO 


AsCl 3 


Trimethyl-arsine, .... 


AsMe 3 


AsClg 


Monomethyl arsenic oxide, 


AsMe0 2 


ASC1 5 


Kakodylic acid, .... 


HAsMeoO., 


HAs0 3 (?) 


Sulphokakodylic acid, . 


(AsMe 2 ) 2 S 3 


AS 2 Og 


Kakodyle trichloride, . 


AsMe.,Cl s 


AsCl 5 


Ethyl- kakodylic acid, . 


(AsE 2 ) 3 3 


As 2 5 


Arsenic triethoxide, 


AsE 3 


AsCl 5 


Tetrethylarsonium oxide, 


(AsE 4 ) 2 


As 2 5 


Dimethyl-diethylarsoriium oxide, . 


(AsMe o E.,),0 


As 2 O g 


Triborethyle, 


BE 3 


BOl 3 


Boric methide, .... 


BMe 3 


BC1 3 


Silicium-ethyle, .... 


SiE 4 


SiCl 4 


Silicium-methyle, . 


SiMe 4 


SiCl 4 



These compounds are evidently formed upon the types of the inorganic 
combinations of the respective elements. Those elements which combine 
in only one proportion with oxygen or sulphur, also combine in one pro- 
portion with an alcohol-radical; whilst those which form more than one 
compound with oxygen and sulphur also generally form corresponding 
compounds with alcohol-radicals. 

Thus zinc, which combines with only 2 atoms of chlorine or bromine, 
also associates itself with 2 of methyle, ethyle, or amyle. Aluminium 
also combines only in one proportion with the alcohol-radicals, but that 
proportion corresponds with the composition of alumina, the only oxide 
of aluminium. 

Tin, on the other hand, forms three distinct series of compounds with 
the alcohol-radicals, composed according to the types of SnO, Sn 2 3 and 
Sn0 2 , respectively. And it must be observed that as long as the type is 
adhered to, the particular radical occupying a place in the compound 
appears to be a matter of indifference; thus we find, in the bodies com- 
posed after the type of Sn 2 3 , one in which the places of the 3 atoms of 
oxygen are occupied by ethyle, and another in which only two of the 
places are occupied by ethyle (an electro-positive or quasi-metallic or 
lasylous radical), whilst the third is filled by iodine (an electro-negative 
or chlorous radical). 



ORGANIC ALKAKOIDS— AMMONIA DERIVATIVES. 

383. The attraction which the vegetable alkaloids have always possessed 
for the chemical inquirer is easily accounted for; composing, as they do, so 
very small a portion of the plants in which they are found, and yet repre- 
senting, in many cases, the whole virtue and activity of such plants in 
their action upon the animal body, it is very natural that their composi- 
tion should have been very carefully studied, with a view to explain the 
changes by which they are produced in the plants, and, if possible, to 
imitate those changes in order to obtain these valuable remedies by arti- 
ficial means. In this study, however, the chemist has to contend with 
difficulties of no insignificant character; for even in the determination of 
the ultimate composition of these alkaloids, their high molecular weights 



540 



COMPOSITION OF THE ALKALOIDS. 



and comparatively small proportion of hydrogen render the exact determin- 
ation of this element a matter of great difficulty, so that even at the 
present time the composition of some of the less known alkaloids can 
hardly be said to be definitely established. 

The following table includes the most important of those alkaloids 
which are extracted from plants : — 



Alkaloid. 


Source. 


Formula. 


Morphine 


Opium 


C 17 H 19 N0 3 


Codeine 


5 J 


C 18 H 21 N0 3 


Narcotine 


, , 


C 22 H 23 N0 7 


Papaverine 




C 20 H 21 NO 4 


Quinine 


Cinchona bark . 


C 20 H 24 N 2 O 2 


Cinchonine 


,, ... 


C 20 H 24 N 2 O 


Quinidine 


,, ... 


C 20 H 24 N 2 O 2 


Quinamine 


5 3 ... 


C 19 H 24 N 2 2 


Caffeine 
Theine 


Coffee .... 
Tea 


j C 8 H 10 N 4 O 2 


Theobromine 


Cacao-nut .... 


C 7 H 8 N 4 2 


Strychnine 


Nux vomica 


C 21 Ho 2 N 9 2 


Brucine 


,, .... 


C 23 H; fi N 2 4 


Nicotine 


Tobacco . 


^10"-14^2 


Solanine 


Potato -shoots 


C 43 H 71 N0 16 


Atropine 


Deadly-nightshade 


| C 17 H 23 N0 3 


Daturine 


Stramonium 


Cocaine 


Coca-leaves .... 


C ]7 H n N0 4 


Hyoscyamine 


Henbane .... 


c 15 h; 3 no 3 


Emetine 


Ipecacuanha 


C 30 H 41 N 2 O 4 


Aconitine 


Aconite . 


C 27 H 39 NO 10 


Vera trine 


White hellebore . 


C 32 H 52 N 2 8 


Coniine 


Hemlock . 


C 8 H 15 N 


Piperine 


Pepper . . . . 


C 17 H 19 N0 3 


Capsicine 


Cayenne pepper . 




Sparteine 


Common broom . 


^15^26^2 


Curarine 


Curara poison 


^10^15^ 


Pilocarpine 


Jaborandi leaves . 


C u H 16 N 8 O a 


om this table it i 


3 seen that the alkaloids invs 


iriably contain nitr 



and though this element generally forms a comparatively small part of the 
weight of the alkaloid, not exceeding 31 per cent, in theobromine, which 
is the richest in nitrogen, and falling as low as 3 "4 per cent, in narcotine, 
which is the poorest, it is from this element that chemists have always started 
in their speculations upon the constitution of these important bodies. 

The earliest view of any importance respecting the constitution of the 
alkaloids was that of Berzelius, who, resting upon the constant presence 
of nitrogen and hydrogen in these substances, regarded them as compounds 
of certain neutral substances (then unknown in the separate state) with 
ammonia, to which they owed their alkaline characters, and this opinion 
was much strengthened when it was discovered that certain organic bases 
(though not those actually found in plants) could be produced by the 
direct combination of ammonia with neutral substances ; thus oil of 
mustard (C 4 H 5 NS), when combined with ammonia (NH 3 ), yields the base 
thioslnnamine (C 4 H S N 2 S). 

To this view it was objected, that ammonia could not be detected in 
these organic bases, and as the doctrine of the displacement of one element 
by another, or by a quasi-element, gained ground, it was suggested that 
the organic bases might be really constituted in the same manner as 



ETHYL ATED AMMONIAS. 541 

ammonia itself, the place of a portion of the hydrogen being occupied by 
a group composed of carbon and hydrogen, or of carbon, hydrogen, and 
oxygen. This view of the constitution of the alkaloids, therefore, would 
at once propose ammonia as the type of this large class. 

In the earlier attempts to refer the organic bases to ammonia as their 
type, it was said that just as that substance is composed of 4 atoms (1 
of nitrogen and 3 of hydrogen), so are the organic bases, but that these 
contain only 2 separate hydrogen atoms, the place of the third atom of 
that element being occupied by a compound which discharges the 
functions of that third atom of hydrogen, and does not destroy the alka- 
line character of the original ammonia type. 

To apply this view to one of the least complex of the organic bases, 
aniline (C 6 H 7 ^T), we might represent it as ammonia (NH 3 ), in which the 
third atom of hydrogen had been displaced by the hypothetical compound 
radical phenyle (C 6 H 5 ) for CgH^N = NH 2 .C 6 H 5 , phenylamiTie. 

This view of the constitution of aniline was supported by the fact, that 
aniline may be obtained by the action of heat upon ammonium phenate, 
thus; NH 4 .C 6 H 5 {Ammonium phenate) — H 2 = XH 2 . C 6 H 5 {Aniline)', and 
as the substances derived from ammoniacal salts by the loss of a mole- 
cule of water were called amides (being supposed to contain amidogen, 
jN'By this theory was spoken of as the amide-theory of the constitution 
of organic bases. 

Later research has only extended this theory, having proved that 
ammonia is the type of at least the greater number of organic bases, and 
that not only one, but all three of the hydrogen-atoms, are movable, and 
may be displaced by compound radicals, whilst even the nitrogen of the 
type also admits of replacement by other elements of the same chemical 
family, viz., by phosphorus, arsenic, and antimony. 

A more instructive example of the elasticity of a type cannot be given. 

384. Ethylated ammonias and their derivatives. — When ethyle iodide 
(C 2 H 5 I) is heated in a sealed tube with an alcoholic solution of ammonia, 
in the proportion of single molecules, a crystalline compound is formed, 
which might at first be regarded merely as a combination of the two 
bodies employed to produce it (C 2 H 5 LNH 3 ) ; but when this substance is 
distilled with potash, it furnishes, instead of ammoniacal gas, a vapour 
which condenses, under the ordinary pressure, in a receiver cooled by 
ice, to a very light colourless liquid which boils at 65° '6 F., and has a 
powerful ammoniacal odour. By analysis, this liquid is found to have 
the composition C 2 H 7 jN", being, in fact, ammonia in which one-third of the 
hydrogen has been displaced by ethyle. That this is the true view of its 
constitution does not admit of a doubt, since it so nearly resembles 
ammonia in all its characters, that it might easily be mistaken for that 
substance. The ethyl-ammonia or ethylia, or ethylamine, has not only the 
modified odour of ammonia, but it is powerfully alkaline, and combines 
readily with acids, forming salts, many of which may be crystallised. It 
is, as might be expected, more inflammable than ammonia. 

The crystalline compound formed by the action of ethyle iodide upon 
ammonia is the ethylamine hydriodate — 

( H I C,H, 

C 2 H,I + N.' H = 2s T { H V.HI, 
IH I H ' 



542 TETRETHYLIUM. 

the hydrogen expelled from the ammonia having taken the place of the 
ethyle in the iodide, forming hydriodic acid, which remains in combina- 
tion with the ethylamine. 

Ethyle chloride and bromide, when heated with ammonia, yield, 
respectively, the hydrochlorate 'and hydrobromate of ethylamine, but 
the ethyle iodide is preferred for this and similar experiments, as being 
less volatile, and therefore more manageable in sealed tubes. 

If ethylamine be again acted upon by ethyle iodide, a second atom of 
hydrogen may be displaced by ethyle, and the hydriodate of diethyla- 
mine is obtained — 

2 H 5 ) ( C 2 H 5 ] 

H \ + C 2 H 6 I = s\ C 2 H 6 >.HI, 
H ) ( H j 

Ethylamine. iodidp Diethylamine hydriodate. 

and from the hydriodate the diethylamine is obtained by distillation with 
potash, as a colourless and inflammable liquid, strongly ammouiacal, and 
having a much higher boiling-point than ethylamine (134° "6 F.). In its 
chemical relations diethylamine is a decided ammonia. 

In order to remove the third atom of hydrogen, it is only necessary to 
subject diethylamine to the action of ethyle iodide — 

IQfii) (C 2 H 5 ) 

^C 2 H 5 l + C 2 H 6 I = N^C 2 HA.HI, 
I Hj (C 2 Hj 

Diethylamine. iodide Triethylamine hydriodate. 

When this last hydriodate is distilled with potash, the triethylamine is 
obtained as a colourless liquid, presenting the strongest evidence of its 
relationship to ethylamine and diethylamine as well as to ammonia. It 
is powerfully alkaline, and boils at a higher temperature than diethylamine. 

But the action of ethyle iodide does not stop here, for if triethylamine 
be again heated with it, a molecule of that base combines with a mole- 
cule of the iodide to form the compound N(C 2 H 5 ) 3 .C 2 H 5 I, which may be 
represented as triethylamine hydriodate, in which the place of the hydrogen 
in the hydriodic acid is occupied by ethyle. 

But it will be remembered that the hydriodate of ammonia (NH 3 .HI) 
is regarded as the iodide of a hypothetical compound metal ammonium 
(NH 4 ), and it would appear admissible to view the above compound as 
ammonium iodide (NH 4 I), in which the 4 atoms of hydrogen are displaced 
by ethyle ; it would then be called iodide of tetrethylammonium (NE 4 I), 
or tetrethylium iodide. 

That this is the true view of the compound has been inferred from the 
circumstance that the salt, obtained by the action of ethyle chloride on 
dimethylamine, is identical with that resulting from methyle-chloride with 
diethylamine. Its formula must therefore be NE 2 Me 2 Cl, whereas if it 
were formed upon the type of NH 3 .HC1, the former reaction would have 
given the salt NMe 2 E.ECl, and the latter, NE 2 Me. MeCl. 

Unlike the preceding compounds, tetrethylium iodide may be boiled 
with solution of potash without decomposition, but if a solution of this 
substance be treated with silver oxide, silver iodide is formed, and when 
the solution is filtered and evaporated in vacuo over sulphuric acid, it 
deposits needle-like crystals having the composition N(C 2 H 5 ) 4 HO. This 



AMMONIA BASES. 543 

substance, which is called the tetrethylium hydrate, is exactly similar in 
properties to the hydrates of potassium and sodium; it is deliquescent, 
absorbs carbonic acid gas eagerly from the air, is exceedingly alkaline 
and caustic, expels ammonia from its salts,, forms soap with the fats, and 
behaves in every respect like a fixed alkali. Its taste is very bitter as 
well as alkaline. 

It is obviously not an ammonia, but is composed after the type of 
caustic potash (KHO), and contains, in place of the potassium, the 
hypothetical radical tetrethylium N(C 2 H 5 ) 4 , or ammonium (2s H 4 ), in 
which the 4 atoms of hydrogen have been displaced by ethyle. 

The action of oxide of silver upon the tetrethylium iodide is now 
intelligible — 

2NE 4 I + Ag 2 + H 2 --= 2NE 4 HO + 2AgI . 

Tetrethylium iodide. Tetrethylium hydrate. 

The new alkali is easily decomposed; eveu at a temperature below the 
boiling-point of water, it is resolved into triethylamine, olefiant gas, and 
water ; N(C 2 H 5 ) 4 HO = N(C 2 H 5 ) 3 + C 2 H 4 + H 2 0. 

It will be remembered that the solution of ammonia in water may be 
regarded as containing ammonium hydrate, NH 3 + H 2 = NH 4 HO, which 
latter would be the true type of tetrethylium hydrate, but so great is 
the want of stability in this case, that all attempts to isolate ammonium 
hydrate have resulted in the production of ammonia and water. 

Like potash, tetrethylium hydrate is capable of forming salts with the 
acids — 

Potassium sulphate, . . K 2 S0 4 

Tetrethylium sulphate, . . (JS"E 4 ) 2 S0 4 . 

It would naturally be expected that by the action of the iodides of 
other alcohol-radicals upon ammonia, compounds should be obtained 
corresponding to those belonging to the ethyle series; thus we have — 
( Type ; ammonia NH 3 ). 

Diamylamine, NH.(C s H n ) 2 



Trimethylamine, N(CH S ) 3 
Triethylamine, N(C 2 H 5 ) 3 
Triamylamine,T JST(C 5 H n ) 3 



Methylamine, 

Ethylamine, 

Amylamine, 

Dimethylamine, NH^CHjg 

Diethylamine, NH.(C 2 H 5 ) 2 

{Type ; imaginary ammonium hydrate, NH 4 HO). 

Hydrate of — 

Tetramethylium, N(CH 3 ) 4 HO 

Tetrethylium, N(C 2 H 5 ) 4 HO 

Tetramylium, N(C 5 H la ) 4 HO . 

But even here, the elasticity of the types and the replacing power of 
the alcohol-radicals are not exhausted. 

If methylamine (NH 2 .Me) be acted upon by ethyle iodide, the hydrio- 
date of metliyl-ethylamine is formed — 

NH 2 .Me + EI = NHMeKHI, 

and by distilling this with potash, the methyl-ethylamine, much resem- 
bling the other ammonia bases, is obtained. 

* Methylamine, which is a gas at the ordinary temperature, is far more soluble in water 
than any other gas ; water dissolves 1150 volumes of methylamine, the solution exactly 
resembling that of ammonia, 

+ Even the hypothetical hydrocarbon cetyle (C 16 H 33 ), the radical of ethal, has been sub- 
stituted for the nitrogen in ammonia. The base tricetylamine, N(C 16 H 33 ) 3 , which is thus 
formed, contains only 2 per cent, of nitrogen. 



544 PHENYLAMINE. 

Again*, on subjecting this base to tbe action of amyle iodide, and dis- 
tilling the product with potash, a new ammonia base is procured, in which 
all 3 atoms of hydrogen are replaced by different radicals ; this base is 
called methyl-ethyl-amylamine, and its composition is represented by the 
formula N(CH 3 ) (C 2 H B ) (CgH^) = NMeEAyl. 

If we had started with aniline (phenylaraine, NH 2 .C 6 H 5 ) in the above 
experiment, treatment with methyle iodide would have furnished methyl- 
aniline or raethyl-phenylamine, iS"H.C 6 H 5 CH 3 ; and by treating this with 
ethyle iodide, we should obtain ethyl-methyl-phenylamine, NC 6 H 5 .CH 3 . 
C 2 H 5 ; the action of amyle iodide upon this last ammonia would give 
methyl-ethyl-amylo-phenylium iodide, and on decomposing this with silver 
oxide, there would be obtained methyl-ethyl-am ylo-phenvlium hydrate 
N(CH 3 ) (C 2 H 5 ) (C 5 H n ) (C 6 H 5 )HO, a base formed upon the hypothetical 
type of ammonium hydrate, in which each of the 4 atoms of hydrogen is 
replaced by a different radical. 

This complex substance affords an excellent example of the difference 
between an empirical and a rational formula ; its empirical formula, 
C 14 H 25 NO, which simply shows the result of its ultimate analysis, teaches 
nothing with respect to its constitution, which is at once clear when the 
rational formula as above written is placed before us. 

Phenylamine, NH 2 (C 6 H 5 ), is found among the products of the destructive distilla- 
tion of rosanillne (page 461), whilst ethyle-rosaniline (aniline-violet) yields ethyl- 
phenylamine or ethyl-aniline, NH(C 6 H 5 ) (C. 2 H 5 ), and phenyl rosaniline (aniline blue) 
yields di-phenylamine ox phenyl aniline, NH(C 6 H 5 ) 2 . 

Diphenylamine has also been obtained by digesting aniline hydrochlorate with 
free aniline at a high temperature, when diphenylamine hydrochlorate is obtained, 
which is decomposed by a large excess of warm water, the diphenylamine rising to 
the surface as an oil which solidifies on cooling. The change may be. expressed, by 
the following equation : — 

NK,(C 6 H 5 ).HC1 + NH 2 (C 6 H 5 ) = NH(C 6 H 5 ) 2 .HC1 + NH 3 . 
Aniline hydrochlorate. Aniline. ^oSStef 

By boiling diphenylamine with benzyle chloride, benzyldiphenylamine is ob- 
tained — 

NH(C 6 H 5 ) 2 + C 7 H 7 C1 = NC 7 H 7 (C 6 H 5 ) 2 + HC1 . 

By heating the new product with hydrochloric and arsenic acids, it is converted into 
a fine green dye, known as viridine or alkali-green. 

Ditoluylamine, NH(C 7 H 7 ) 2 , may be procured in a similar way by digesting toluidine 
hydrochlorate with toluidine. 

Phenyl-toluylamine, NH(C 6 H 5 ) (C 6 H 7 ), is formed by the action of aniline on 
toluidine hydrochlorate, or by that of toluidine on aniline hydrochlorate. 

Under the action of nitric acid, di-phenylamine gives rise to di-nitro-diphenyla- 
mine, NH[C 6 H 4 (N0 2 )] 2 , in which the same type is preserved though nitric peroxide 
(N0 2 ) is substituted for one-fifth of the hydrogen in the phenyle. The intense blue 
colour which is produced renders the diphenylamine a most delicate test for nitric 
acid. 

When heated with benzoyle chloride (C 7 H 5 0.C1), diphenylamine yields diphenyl- 
benzoylamine, N(C 6 H 5 ) 2 (C 7 H 5 0). 

It will be observed that certain of these bases derived from the alcohols 
have the same empirical formulae as those derived from coal-tar and other 
sources, with which, however, they are by no means identical. Thus, tolui- 
dine (C 7 H 9 N) has the same composition as methyl-aniline (NH.C 6 H 5 .CH 3 ) ; 
but the former is a crystalline solid, and the latter an oily liquid. 
Again, when ethyle iodide acts upon toluidine, an atom of hydrogen is 
displaced by ethyle, and ethylo-toluidine is obtained. The composition 
of this base, C r H s (C 2 H 5 )N, is the same as that of methyl-ethyl-aniline, 



POLY-AMMONIAS. 545 

X(CH 3 )(C 2 H 5 ) (C 6 H 5 ), and as that of cuinidine (C,H 13 X) ; but in their 
chemical properties these bodies exhibit such a difference as would be 
expected from the difference in their constitution. 

385. Investigation of the constitution of the alkaloids. — It will be 
evident that the principles developed in the experiments just described 
may be applied in investigating the constitution of the bases extracted 
from plants. Let it be supposed that ethylamine (C 2 H r X) was a vege- 
table alkali of unknown constitution ; when it was found that by the 
action of ethyle iodide 2 out of the 7 atoms of hydrogen could be dis- 
placed, it would be at once inferred that these 2 atoms occupied a very 
different position from the other 5, and that the constitution of the 
compound would be more properly expressed by writing the formula 
C 2 H 5 .H 2 X. On applying the same principle to the examination of the 
natural alkaloid coniine (C 8 H ]5 N), it was found possible, by the action of 
methyle iodide, to remove only 1 atom of the hydrogen, so that the 
formula C 8 H U .HX would more correctly represent the constitution of 
coniine, which might be then regarded as ammonia in which 2 atoms of 
the hydrogen have been displaced by the group C 8 H U , or in which 
each of these atoms has been displaced by the group C 4 H 7 . 

If we were acquainted with an iodide of this group, we have every 
reason to expect that its action upon ammonia would lead us to the artificial 
formation of coniine. 

Xicotine, morphine, and codeine, when acted upon by the iodides of 
alchohol-radicals, yield iodides upon the type XH 4 I, from which may be 
obtained fixed alkalies resembling tetrethylium hydrate. Thus we have — 

Methyl-morphyl-ammonium hydrate, X(C lV H 19 3 )'''(CH 3 )HO 
Ethyl-codyl-ammonium „ X(0 18 H 21 O 3 )'"(C 2 H 5 )HO 

Ethyl-nicotyl-ammonium „ X(C 5 H r )'"(C 2 H 5 )HO . 

Monamines, as the bases formed on the type of one molecule of ammonia 
are called, are classified as primary, secondary, and tertiary monamines, 
accordingly as one, two, or three of the hydrogen atoms of the ammonia 
have been replaced by another radical They may be distinguished by 
heating their hydrochlorates with silver nitrite. 

A primary monamine then yields the corresponding alcohol; thus 
NH 2 C 2 H 5 .HC1 (ethylamine kydrochlorate) + AgN0 2 = C 2 H 5 OH (ethyle- 
alcohol) + AgCl + H 2 + N 2 . 

A secondary monamine yields a " nitroso-compound ;" XH(C 2 H 5 ) 2 .HC1 
(di-ethylamine hydrochlorate) + AgX0 2 = X(C 2 H 5 ) 2 XO (nitroso-diethy- 
lamine) + AgCl + H 2 0. 

A tertiary monamine is not decomposed by silver nitrite. 

386. Poly ammonias. — In speculating upon the constitution of the 
vegetable bases, it must not be forgotten that some of them contain 
2 atoms of nitrogen; this is the case, for example, with cinchonine 
(C 20 H 24 X 2 O), quinine (C 20 H 24 X 2 O 2 ), and strychnine (C 21 H 22 X 2 2 ). If 
the whole of the nitrogen in these bases be due to the ammonia type, 
they must be composed after the type of a double atom of ammonia, 
X 2 H 6 . In the case of strychnine, it is found that the action of ethyle 
iodide fails to remove any portion of the hydrogen, so that if the base be 
really composed after the ammonia type, it must be represented by 2 atoms 
of ammonia (X 2 H 6 ), in which the whole of the hydrogen has been dis- 

2 M 



546 DIAMINES. 

placed by the group (C 21 H 22 2 ), when its formula would be N 2 (C 21 H 22 O a ) v1 , 
the replacing group in this case being hexatomic, or equivalent to 6 atoms 
of hydrogen. That it is by no means necessary for each atom of hydrogen 
to be displaced by a single group or radical, is seen in a great many organic 
compounds; thus, in chloroform (CH)C1 3 , we have the triatomic group 
CH (commonly called formyle) occupying the position of 3 atoms of 
hydrogen which would be required to combine with the 3 atoms of 
chlorine ; again, in Dutch liquid (C 2 H 4 )C1 2 , we have the diatomic group 
C 2 H 4 (ethylene) occupying the place of 2 atoms of hydrogen. 

If the view above explained with respect to the constitution of some of 
the natural alkaloids be correct, it ought to be possible to form artificially 
a base in which 2 or 3 atoms of hydrogen have been displaced by means 
of a diatomic or triatomic radical. 

387. Diamines. — When olefiant gas or ethylene, C 2 H 4 , is brought in 
contact with bromine, the compound C 2 H 4 Br 2 , corresponding to Dutch 
liquid (C 2 H 4 C1 2 ), is obtained, and from the action of ammonia upon this 
ethylene dibromide, there is derived a new alkaline base, having the 
composition N 2 H 4 (C 2 H 4 )", or 2 molecules of ammonia (N 2 H 6 ), in which 
the diatomic ethylene replaces 2 atoms of hydrogen. Such bases, formed 
upon the double ammonia type, are called diamines. The base above men- 
tioned is named ethylene-diamine. The diamines, like the double molecule 
of ammonia from which they are derived, are capable of combining with 
2 molecules of hydrochloric or any similar acid, which is implied by 
stating that they are diacid. 

"When Dutch liquid {ethylene dichloridc (C. 2 H 4 )"C1 2 ) is heated to 300° F. with strong 
ammonia in a sealed tube, an action takes place corresponding to that of a double 
molecule of hydrochloric acid (H 2 C1 2 ) upon a double molecule of ammonia (N" 2 H 6 ), 
which would give rise to a double molecule of NH 4 C1 ; in the produet of the action of 
Dutch liquid upon ammonia (N 2 H 4 (C. 2 H 4 ) 2 "C1 2 ), the places of 4 atoms of hydrogen 
are occupied by 2 of the diatomic group (C 2 H 4 ). But here the correspondence ceases, 
for whilst the ammonium chloride, when decomposed with silver oxide, would yield 
ammonia and silver chloride, the new compound, when thus treated, yields a fixed alka- 
line base, resembling caustic potash, and having the composition N 2 H 4 (C 2 H 4 ). 2 ".H 2 0. 2 , 
which represents a double molecule of the hypothetical ammonium hydrate 2(NH 4 HO), 
in which 4 atoms of hydrogen have been displaced by 2 of the diatomic ethylene. 
The name diethylene-diammonium hydrate expresses the composition of this substance, ■ 
which is remarkable for its stability, a temperature above 300° F. being required to 
effect its decomposition, when it furnishes a volatile alkali, having the composition 
N" 2 H 2 (C 2 H 4 ) 2 ", and called diethylene-diamine, being evidently formed from a double 
molecule of ammonia, in which four atoms of hydrogen are replaced by two of the 
diatomic ethylene. Its production may be explained by the equation — 

N 2 H 4 (C 2 H 4 ) 2 "H,0 2 - N 2 H 2 (C 2 H 4 ) 2 " + 2H 2 . 

By acting upon the new ammonia with ethyle iodide (C 2 H 5 I), the 2 atoms of hydrogen 
may be displaced by ethyle, yielding diethyl-diethylene-dianiine, N 2 (C 2 H 5 ) 2 (C 2 H 4 ) 2 '', or 
a double molecule of ammonia (N 2 H 6 ), in which H 2 are replaced by two of ethyle, 
and H 4 by two of ethylene. 

By treating phenylamine (aniline), NH 2 (C 6 H 5 ), with ethylene dichloride (Dutch 
liquid), the diphenyl-diethylene-diamine, N 2 (C 6 H 5 ) 2 (C. 2 H 4 ) 2 ", is obtained, which repre- 
sents a double molecule of ammonia (N 2 H 6 ), in which H 2 are replaced by two of 
phenyle, and H 4 by two of ethylene. By the action of chloroform upon aniline, 
formyle-diphcnyl-diaminc, N 2 (CH)'"(C 6 H 5 ) 2 H, has been obtained, in which H 3 are re- 
placed by the triatomic formyle (CH), and H 2 by phenyle. 

It has been seen that phenylamine is produced by the deoxidising action of ferrous 
acetate upon nitrobenzene (C (i H 5 lSr0 2 ). When di-nitrobenzene is treated in a similar 
way, %)henylenc-diainine, N 2 H 4 (C 6 H 4 )'', is obtained, which is evidently derived from a 
double molecule of ammonia, in which H 2 are replaced by the diatomic group plicny- 
lene (C 6 H 4 ), which bears the same relation to phenyle (C 6 H 5 ) as ethylene (C 2 H 4 ) 



TRTAMINES OR TRIPLE AMMONIAS. 547 

bears to ethyle (C 2 H 5 ). By treating di-nitrotoluene and di-nitrocumene with ferrous 
acetate, tolylene- diamine and cumylme- diamine are obtained, which are diammonias, 
in which H 2 are replaced by the diatomic radicals tolylene (C 7 H 6 )" and cumylene 
(C 9 H l0 )". These three diamines are called the aromatic diamines, since the diatomic 
groups phenylene, tolylene, and cumylene are closely connected, through benzene 
(C 6 H 6 ), toluene (C 7 H 8 ), and cumene (C 9 H 10 ), with the aromatic acids, benzoic 
(C 7 H 6 2 ), toluic (C 8 H 8 2 ), and cuminic (C 10 HJoO 2 ). 

Paraniline (C 12 H 14 N' 2 ) is obtained as a secondary product in the manufacture of 
aniline, with which it is polymeric. Its properties are very different from those of 
aniline, for it is solid at the ordinary temperature, forming silky needles which melt 
when heated, and boil beyond the range of the thermometer, distilling unchanged. 
It combines with acids, forming beautiful crystalline salts, the study of which proves 
it to be a diamine. 

388. Triamines. — The triamines are formed upon the type of a treble 
molecule of ammonia (N 3 H 9 ), in which the hydrogen is replaced 
either entirely or in part by other radicals. Thus, diethylene-triamine, 
]N" 3 H 5 (C 2 H 4 ) 2 ", and triethylene-triamine, N 3 rT 3 (C 2 H 4 )'' 3 , are obtained by 
the action of ethylene di-bromide (C 2 H 4 Br 2 ) upon ammonia. They are 
powerfully alkaline liquids, which are capable of absorbing carbonic acid 
gas from the air. The triamines are generally capable of forming three 
classes of salts, the monacid, diacid, and triacid salts, containing respec- 
tively one, two, and three molecules of acid. 

Di-ethylene-di-ethyl-triamine, N 3 H 3 (C 2 H 4 )./(C 2 H 5 ) 2 , is produced by the joint action 
of ethylamine and ammonia upon ethylene dibromide — 

2(C 2 H 4 )Br 2 + 3NH 2 (C 2 H 5 ) + NH 3 
= N 3 H 3 (C 2 H 4 ). 2 "(C 2 H 5 ) 2 .3HBr + NH 2 (C 2 H 5 ).HBr . 

It forms splendidly crystallised salts, and is evidently derived from 3 molecules of 
ammonia (N 3 H 9 ), by the substitution of (C 2 H 4 ) 2 " for H 4 , and of (C 2 H 5 ) 2 for H 2 . 

Carbotriamine (guanidine), N 3 H 5 C iv , is a treble molecule of ammonia, in which 
4 atoms of hydrogen are replaced by 1 atom of tetratomic carbon. It is formed by 
heating ammonia with ethyl subcarbonate in a sealed tube to about 300° F. 

2(C 2 H 5 ) 2 O.C0 2 + 3NH 3 + H 2 = N 3 H 5 C.H 2 + 4(C 2 H 5 .HO). 

The change is more clearly explained by representing the ethyle subcarbonate as 
formed upon the type of 4 molecules of water (H 8 4 ) in which H 4 are replaced by 
(C 2 H 5 ) 4 , and the remaining H 4 by C . 

(C 2 Hg/ J ^ + 3XHs + jj^q = ^^oj^o + (C 2 H 5 ) 4 J Q ^ 

Ethyle subcarbonate. Guanidine. 4 mols. alcohol. 

Guanidine may also be obtained by heating chloropicrine in a sealed tube, with an 
alcoholic solution of ammonia, to 212° F., when the following reaction ensues — 

2CC1 3 (N0 2 ) + 6NH 3 = 2(N 3 H g C.HCl) = + 4HC1 + K>0 3 + H 2 . 

Cloropicrine. Guanidine hydrochlorate. 

It will be remembered that ethyle subcarbonate itself is obtained by the action of 
sodium upon an alcoholic solution of chloropicrine (page 528). 

Guanidine is also formed by heating ammonium sulphocyanide for two hours to 
190°-200° C. 

3NH 4 CNS = N 3 H 5 C. HCNS {Guanidine sulphocyanate) + 2NH 3 + CS 2 . 

Melaniline, C W H 13 ;N" 3 , a crystalline base, produced by the action of cyanogen 
chloride upon aniline, may be regarded as diphenyl- guanidine, N 3 H 3 (C 6 H 5 ) 2 C, or 
guanidine in which two of phenyle have replaced two of hydrogen. 

The beautiful aniline dyes appear to be salts of certain triamines formed by the 
replacement of the hydrogen in a treble molecule of ammonia by hydrocarbon 
radicals. 

According to Hofmann, rosaniline, the base of the aniline red produced by the 
action of oxidising agents upon aniline containing toluidine, is possibly phenylene- 
ditolylene-triamine, is" 3 (C 6 H4)"(C 7 H 6 ) 2 "H 3 .H 2 0, the phenylene being derived from the 
aniline, NH 2 (C 6 H 5 ), and the tolylene from the toluidine, NH 2 (C 7 H 7 ). Aniline bine, 
formed by the action of aniline upon aniline red, would be pJienylene-ditolyleneo 



548 TETRAMINES. 

triphenyl-triaminc, N 3 (C 6 H 4 )"(C 7 H 6 ). 2 "(C 6 H 5 ) 3 .H 2 0, having been formed from rosani- 
line by the substitution of three of phenyle for H 3 . Aniline violet, the result of 
the action of ethyle iodide upon rosaniline, would be phenylene-ditolylcne-triethyl- 
triamine, N 3 (C 6 H 4 )"(C 7 H 6 ) 2 "(C 2 H 5 ) 3 .H 2 0, or rosaniline containing three of ethyle in 
place of H 3 . 

The trichloride of diethylene-triammonium, N 3 (C 2 H 4 )./H 8 .C1 3 , has also been ob- 
tained. 

389. Tetramines are formed upon the type of 4 molecules of ammonia, 
and therefore contain 4 atoms of nitrogen, and are able to combine with 4 
molecules of a hydrogen acid. Thus, if ethylene dibromide be allowed to 
act upon ethylene-diamine in the presence of hydrobroniic acid, the hydro- 
bromate of triethylene-tetramine is obtained — 

(C 2 H 4 )"Br 2 + 2N 2 (C 2 H 4 )''H 4 + 2HBr = ¥ 4 (C 2 H 4 ) 3 ''H 6 .4HBr 

Ethylene dibromide. Ethylene-diamine. Triethylene-tetramine hydrobromate, 

and if this be decomposed with silver oxide, a strongly alkaline solution 
is obtained, which contains triethylene-tetramine, N 4 (C 2 H 4 ) 3 "H fi , or a 
quadruple molecule of ammonia (N 4 H 12 ), in which half of the hydrogen 
is replaced by three of diatomic ethylene. 

By acting on C 2 H 4 Br 2 with ethylamine, a salt is obtained, having the composi- 
tion !Sr 4 (C 2 H 4 ) g "(C 2 H 5 ) 4 H 2 ,Br 4 , representing 4 molecules of ammonium bromide 
(N 4 H lfi Br 4 )", in which H 10 are replaced by 5(C 2 H 4 )", and H 4 by (C 2 H 5 ) 4 . From this 
bromide a strongly alkaline base, pentethylene-tetrethyl-teirammonium hydrate 
[N 4 (C 2 H 4 ) 5 "(C 2 H 5 ) 4 H 2 ]H 4 4 is obtained, which is formed upon the type of 4 molecules 
of the imaginary ammonium hydrate (JSTH 4 HO). 

The aetion of ethyle iodide (C.,H 5 I) upon this base replaces each of the remaining 
atoms of hvdrogenby ethyle, yielding (N 4 (C 2 H 4 ) g "(C 2 H 6 ),H]H 4 4 , and [N 4 (C 2 H 4 ) 5 " 
(C a H 5 ) 6 ]H 4 b 4 . 

When diethylamine NH(C 2 H 5 ) 2 acts upon ethylene dibromide, the bromide of 
tri-ethylene-oetethyl-tetrammonium, N 4 (C 2 H 4 ) 3 "(C 2 H 5 ) 8 H 2 .Br + . is obtained, which also 
furnishes a powerfully alkaline base [N 4 (C 2 H 4 ) 3 "(C 2 H 5 ) 8 H 2 ]H 4 4 . 

390. We are not entirely dependent upon purely artificial processes for 
the ammonia bases containing alcohol-radicals. Many processes of putre- 
faction furnish certain of these bases which had hitherto been overlooked 
in consequence of their resemblance to ammonia. Thus, putrefying flour 
yields ethylamine, trimethylamine, and amylamine ; trimethylamine is also 
found in the roe of herrings, as also in putrefied urine and in the Cheno- 
podium vulvaria ; it may also be obtained by distilling ergot of rye with 
potash. Methy famine, ethylamine, propylamine (NH 2 .C 3 H 7 ), hutylamine 
(NH 2 .C 4 H 9 ) or petinine, and amylamine, are found among the products of 
the destructive distillation of bones. 

Trimethylamine is obtained in quantity by distilling the refuse or vinasses of the 
French beet-sugar refineries. It is used for converting potassium chloride into 
potassium carbonate by a process resembling the ammonia-soda process (p. 264), 
which depends on the fact that bicarbonate of soda is less soluble in water than sal- 
ammoniac ; but bicarbonate of potash has about the same solubility as sal-ammoniac, 
so that trimethylamine, whose hydrochlorate is much more soluble than that of 
ammonia, is substituted for the latter. The hydrochlorate of trimethylamine is 
used as a source of rnethyle chloride, which is obtained from it by distillation ; 
3NMe 3 HCl = 2MeCl + 2NMe 3 + NH 2 Me + HCl. The MeCl comes off as a gas which 
is condensed b}' a pressure of about four atmospheres into an ethereal liquid, 
boiling at - 23°*C. 

It is used for making aniline colours and for producing artificial cold. 

By the action of trimethylamine on ethylene oxide in the presence of water, a 
strongly alkaline base is obtained, which is known as choline or neurine, and 
was originally found in bile, but is extracted in larger quantity from the brain ; 
N(CH 3 ) 8 + C 2 H 4 + H 2 = C 5 H 15 N0 2 {neurine). 



TRIETHYLPHOSPHINE. 549 

391. Ammonias and ammonium bases containing phosphorus, arsenic, 
and antimony. — It might be expected that the ammonia type was not 
susceptible of any further modifications, but it has been found that even 
the nitrogen of that type may be represented by other elements which are 
chemically related to it. 

Antimony, arsenic, and phosphorus, it will be remembered, all form 
compounds with 3 atoms of hydrogen, SbH 3 , AsH 3 , and PH 3 , which may 
be regarded as formed upon the ammonia type. Neither of these sub- 
stances, however, possesses any alkaline character, the last alone being 
capable of combining with certain acids (hydrobromic and hydriodic). 

Mention has already been made of the circumstance that compounds 
corresponding to antimonietted, arsenietted, and phosphuretted hydrogen 
may be obtained, in which the place of the hydrogen is occupied by cer- 
tain alcohol-radicals ; but in these cases the hydrogen does not admit of 
partial replacement, only those compounds which correspond to triethyla- 
mine and trimethylamine having been obtained. 

Triethylstibine, Sb(C 2 H 5 ) 3 , and triethylarsine, As(C 2 H 5 ) 3 , have already 
been noticed amongst another class of bodies to which they seem properly 
to belong, since they are not capable of forming salts corresponding to 
those of ammonia (see page 536). 

With triethylphosphine, however, the case is different ; this substance, 
P(C 2 H 5 ) 3 , is a true ammonia, capable of forming salts with the acids, like 
ethylamine, although exhibiting, unlike that body, a very powerful ten- 
dency to combine directly with an atom of oxygen or sulphur, to form 
compounds resembling those of the arsenic and antimony series (see 
page 536), and formed upon the type of phosphoric chloride (PC1 5 ). 
Thus we have — 

Triethylphosphine oxide, . . PE 3 
Sulphide, PE 3 S, 

and the corresponding compounds containing methyle. 

Triethylphosphine is obtained by the action of phosphorus trichloride 
upon zinc-ethyle, 2PC1 3 + 3ZnE 9 = 2PE 3 + 3ZnCl 2 . It is a volatile liquid 
of a very peculiar powerful odour, the vapour of which, when mixed 
with oxygen, explodes with great violence at a temperature far below 
212°. 

By acting upon triethylstibine, or stibio-triethyle, with ethyle iodide, 
an iodide is obtained which, when decomposed by silver oxide, yields 
tetrethylstibonium hydrate (SbE 4 HO), formed after the type of ammonium 
hydrate (NH 4 HO). 

In a similar manner there are obtained tetrethylarsonium hydrate 
(AsE 4 HO) and tetrethylphosphonium hydrate (PE 4 HO), and their corre- 
sponding methyle compounds. 

These substances are precisely similar in properties to tetrethylium 
hydrate, being powerfully caustic alkalies bearing a close resemblance to 
caustic potash. 

A very remarkable base has also been obtained, composed after the type 
of a double molecule of the imaginary ammonium hydrate (N 2 II 8 H 2 2 ), 
in which 1 atom of nitrogen has been replaced by phosphorus, and the 
other by arsenic, whilst, of the hydrogen, 2 atoms are replaced by the 
diatomic radical ethylene (C 2 H 4 )", and the remainder by ethyle. This 
base has been styled ethylene-hexethyle-diphospharsonium hydrate, and 
its formula is PAs(C 2 H 4 )"(C 2 H 5 ) 6 H 2 02. It combines with 2 molecules 



550 AMIDES. 

of acids to form salts, and behaves in every respect as a double molecule 
of caustic potash would do. 

By acting upon triethylphosphine with chloroform (CHC1 3 ) containing 
the triatomic radical formyle (CH)'", a chloride has been obtained which 
is composed upon the type of 3 molecules of ammonium chloride (3NH 4 C1 
= N 3 H 12 C1 3 ), in which one-fourth of the hydrogen is replaced by formyle 
and the rest by ethyle ; the composition of this chloride is therefore 
(P 3 (CH)'"(C 2 H 5 ) 9 C1 3 ) ; from this compound various salts have been ob- 
tained, containing the corresponding oxide combined with 3 molecules of 
the acids, but the hydrate itself has not been obtained — 

3P(C 9 H 5 ) 3 + (CH)'"C1 3 = P 3 (CH)"'(C 2 H 5 ) 9 C1 3 

Triethylphosphine. Chloroform. ^^osX^ 6 ^ 

392. The insight into the constitution of the bases derived from ammonia, which 
has been acquired in the researches detailed above, has induced chemists to endeavour 
to apply the same principles to certain inorganic bases derived from ammonia by the 
action of metallic salts. 

Thus, by the action of platinous chloride upon ammonia (see page 396), a compound 
is obtained which may be regarded as simply PtCl 2 (NH 3 ) 2 , but when this is treated 
with silver oxide, the CI is removed in the form of silver chloride, and a caustic 
alkaline base is separated, which has the formula PtO. (NH 3 ) 2 , or rather, viewed 
upon the type of ammonium oxide, N 2 H 6 PtO, platammonium oxide. 

By employing ethylaniine instead of ammonia, there would be obtained N 2 H 4 E 2 PtO, 
ethyloplatammonium oxide. 

When the compound PtCl 2 (NH 3 ) 2 (or rather N 2 H 6 Pt. Cl 2 , platammonium chloride) 
is again treated with ammonia, it yields N 2 H fi Pt.Cl 2 (NH 3 ) 2 , and when this is decom- 
posed with silver oxide, another caustic alkali is obtained, having the composition 
N 2 H 6 Pt(NH 3 ) 2 H 2 2 , which may be regarded as ]ST 2 H 4 Pt(NH 4 ) 2 H 2 2 , platammon- 
ammonium hydrate (diplatosamine hydrate) ; it would then become a double mole- 
cule of ammonium hydrate (NH 4 HO), in which 2 atoms of hydrogen are replaced by 
platinum and 2 by ammonium. 

Very remarkable and beautiful crystalline compounds have also been obtained, which 
are formed after the type of platammonium chloride, but contain either phosphorus, 
antimony, or arsenic, in place of nitrogen, and ethyle in place of hydrogen ; these 
are — 

Plato-tricthyl-diphosphonium chloride, . P 2 Pt(C 2 H 5 ) 6 . Cl 2 

arsonium ,, . As 2 Pt(C 2 H 5 ) 6 .Cl 2 

stibonium ,, . Sb 2 Pt(C 2 H 5 ) 6 .Cl 2 . 

Corresponding salts have also been obtained containing gold in the place of 
platinum, and forming beautiful colourless crystals. 

In some bases, chlorine, bromine, and even nitric peroxide (N0 2 ) have 
been introduced in the place of hydrogen into the alcohol-radical, but in 
all these cases the basic energy is diminished by such substitution, and in 
some altogether destroyed. 

Thus, in the aniline (phenylamine) series, we have — ■ 

Chloraniline, . . . NH 2 (C 6 H 4 C1), weak base. 

Dichlorauiline, . . . NH o (C 6 H 3 Cl ), weaker base. 

Trichloraniline, . . . NH (C 6 H 2 C1 3 ), neutral. 

Nitraniline, . . . NH o [C 6 H 4 (N0,)], weak base. 

Dinitraniline, . . . NH 2 [C 6 H 3 (N0 2 ) 2 ], neutral. 

393. Amides. — When ammonium oxalate (NH 4 ) 2 C 2 4 is subjected to 
distillation, a white, crystalline, sparingly soluble substance is obtained, 
which has been named oxamide, and is represented by the formula 
(ISrH 9 ) 2 2 . This substance is derived from the ammonia-salt by the 
loss of 2 molecules of water (NH 4 ) 2 C 2 4 - 2H 2 = (NH 2 ) 2 C 2 2 , and its 
close relationship to ammonium oxalate is shown by the circumstance 
that it is reconverted into that salt, if heated with water in a sealed tube 



XITRILES. 551 

to 436° F., or by simply boiling it with water to which a little acid or 
alkali has been added. 

Oxamide is more readily prepared by decomposing oxalic ether with 
ammonia, when it is obtained as a white crystalline precipitate — 

(C 2 H 5 ) 2 C 2 4 + 2XH 3 = 2C 2 H 5 HO + (XH 2 ) 2 C 2 2 

Oxalic ether. Alcohol. Oxamide. 

If one of the compound ammonias, such as ethylamine and aniline, be 
employed instead of ammonia, ethyloxamide and oxanilide are produced — 

(C 2 H 5 ) 2 C 2 4 + 2(XH 2 .C 2 H 5 ) = 2C 2 H 5 HO + (XH.C 2 H 5 ) 2 C 2 2 

Oxalic ether. Ethvlamine. Ethvloxamide. 

(C 2 H 5 ) 2 C 2 4 + 2(NH 2 .C 6 H 5 ) = 2C.H 5 HO + (XH.C 6 H 5 ) 2 C 2 2 

Aniline. Oxanilide. 

Oxamide is the representative of a large class of bodies, known as the 
amides, which may be denned as substances capable of being converted, 
by the assimilation of the elements of water, into the ammonium-salts from 
which they are derived. 

Some other interesting members of this class are here enumerated, 
together with the corresponding ammonium-salts — 



Formamide, . . . XH 2 .CHO Ammonium formiate, (XHJ.CHO 



Acetanride, . . . XH o .CoH 3 
Butvramide, . . . NH 2 .C 4 H 7 

Benzamide, . . . XFCC-H 5 



acetate, (XH 4 ) 
butvrate, (XH 4 ).C 4 H-Oo 
benzoate, (XH 4 ).C r H 5 2 

It is evident that these amides may be regarded as derived from ammonia 
by the substitution of a compound group for one of the 3 atoms of 
hydrogen. 

\Yhen hydro-ammonic oxalate (XH 4 HC 2 4 ) is distilled, at a moderate 
heat, a solid acid substance is left in the retort, which is known as oxamic 
acid, XH. 7 .HC 3 , and forms soluble crystallisable salts with lime and 
baryta, both which bases yield insoluble salts with oxalic acid. 

When the solution of oxamic acid in water is boiled, it is reconverted 
into the original oxalate; XH 2 HC 2 3 + H 2 = NH 4 HC 2 4 . 

Oxamic acid is the representative of a limited class of acids formed in a 
similar manner. 

394. NitrUes. — TThen ammonium oxalate is mixed with phosphoric 
anhvdride and distilled, it loses 4 molecules of water, leaving cvanogen 
(XHJ 2 C 2 0,-4H 2 = 2CX. 

In a similar manner, ammonium benzoate yields benzonitrile — 

XH 4 C 7 H 5 2 {Ammonium benzoate) — 2H 2 = C 7 H 5 X {Benzonitrile). 
The new compound is an oil which has a powerful odour of bitter 
almonds, and is reconverted into ammonium benzoate by boiling with 
dilute acids or alkalies. 

The term nitrite is applied to all similar substances which are derived 
from ammoniacal salts by the loss of 2 molecules of water, and are capable 
of reconversion into those salts. Many of these nitriles are isomeric with 
the cyanides of the alcohol-radicals, from which they may, sometimes be 
obtained by the action of a high temperature. 

Oxalonitrile, XC = Oy, cyanogen. 
Formonitrile, XCH = HCy, hydrocyanic acid. 
Acetonitrile, XC 2 H 3 = CIL.CX, methvle cyanide. 
Propionitrile, XCJS'- = C H 5 .CX, ethyle 
Benzonitrile, XC-H 5 = C\IL.CX, phenvle „ 



552 IMIDES. 

The nitriles are distinguished by their ready tranformation into 
ammonia and an acid containing the same number of carbon-atoms as the 
nitrile, under the influence of caustic alkalies; thus — 

C 3 H 5 ¥ + KHO + H 2 = JS T H 3 + KC s H 5 2 

Propionic ile. Potassium propionate. 

Again, diluted acids have little action upon the nitriles, whilst the 
cyanides of the alcohol radicals (or carbamines) are converted into formic 
acid, and an ammonia in which the alcohol radical is substituted for 
hydrogen: thus — 

C 2 H 5 .CN + HC1 + 2H 2 = CH 2 2 + is T H 2 .C 2 H 5 .HCl, 

Ethyle cyanide. Formic acid. Ethylamine hydrochlorate, 

a reaction corresponding to that of hydrocyanic acid with hydrochloric 
acid • HCN + HC1 + 2H 2 = CH 2 2 + NH S .HCL 

A by no means numerous class of substances, frequently spoken of as 
the imides* are obtained by the action of heat upon the acid ammonium 
salts of certain dibasic acids, by the loss of 2 molecules of water, thus — 

NH 4 HC 10 H 14 O 4 - 2H 2 = KttC w H M 0, 

Hydro-ammonic camphorate. Camphorimide. 

395. If the amides be regarded, as immediately derived from ammonia by substi- 
tution, their want of alkaline properties must be ascribed to the introduction of an 
electro-negative radical in place of the hydrogen. 

Thus, if oxalic acid be regarded as H 2 (C. 2 2 )0 2 , then oxamide may be viewed as a 
double molecule of ammonia, in which 2 atoms of hydrogen have been displaced by 

(CA) ; n 2 j ( C A)" 

Again, if benzoic acid and salicylic acid, respectively, be regarded as (C 7 H 5 0)HQ 
and (C 7 H 5 2 )HO, then their amides would be represented as — 

Benzamide, N j (^gO)' Salicylamide, N j ( C r**A)' 

and it should be possible to procure them from ammonia by processes similar to that 
which furnishes ethylamine, &c. It is found that when benzoyle chloride is heated 
with ammonia, benzamide is really produced — 

C 7 H 5 0.C1 {Benzoyle chloride) + 2^H 3 = XH 2 .C 7 H 5 (Benzamide) + KH 4 C1. 

But we ought also to be able to carry the substitution farther by displacing the 
remaining hydrogen ; accordingly, when benzamide and salicylamide are heated 
together, ammonia is disengaged, and benzoyl-salicylamide obtained — 

( C 7 H 5 ( C 7 H 5 0, ( C 7 H 5 

N \ H + N \ H - = N \ C 7 H 5 2 + XH 3 
( H ( H ( H 

Benzamide. Salicylamide. Benzoyl-salicylamide. 

Amides have even been obtained in which the 3 atoms of hydrogen in ammonia are 
displaced by different radicals. 

It is evident that the imides might be regarded as ammonia in which 2 atoms of 
hydrogen have been replaced by a diatomic radical, thus — 



Camphorimide, N j ( C iogiA)" 



and the nitriles, as ammonias in which all the hydrogen has been replaced by a 
triatomic radical, but experimental evidence is scarcely in favour of these views. 

If the amides, be really derivatives from ammonia, it would be expected that 
similar bodies should be derived from phosphine (PH 3 ). An example of these is fur- 
nished by tribenzoi/l-phosphide, P(C 7 H 5 0) 3 , which is obtained by the action of benzoyle 
chloride upon phosphine — 

PH 3 + 3(C 7 H 5 0.C1) = P(C 7 H 5 0) 3 + 3HC1. 

* This designation was originally employed upon the supposition that these bodies eon- 
tain the imaginary radical imidogen, NH ; and, in a similar manner, the amides were 
supposed to contain amidogeu, NH 2 . 



METAL- AMIDES — DERIVATIVES OF THE ALCOHOLS. 553 

396. Metal-amides. — The possibility of substituting metals for the 
hydrogen in ammonia has only recently been fully established, though it 
had long been known that when potassium and sodium were heated in 
gaseous ammonia, hydrogen was evolved, and potassamide and sodamide 
were produced, NH 3 + K = NH 2 K + H. When potassamide is heated, 
ammonia is evolved, and tripotassamide (NK 3 ) produced, 3(NH 9 K) 
= NK 3 + 2NH 3 . 

If ammoniacal gas be passed into an ethereal solution of zinc-ethyle, 
ethyle hydride is evolved, and a white amorphous precipitate of zincamide 
separates; 2NH 3 + (C 2 H 5 ) 2 Zn = (NH 2 ) 2 Zn + 2(C 2 H 5 .H). When zincamide 
is brought in contact with water, it is decomposed with evolution of heat, 
yielding zinc hydrate and ammonia — 

(NH 2 ) 2 Zn + 2H 2 = 2NH S + Zn(HO) 2 . 

The decomposing action of zinc-ethyle upon the bases derived from 
ammonia is parallel with that upon ammonia itself. Thus, with aniline ; 
2(NH 2 .C 6 H 6 ) + (C 2 H 5 ) 2 Zn = (NH) 2 Zn(C 6 H 6 ) 2 + 2(C 2 H 5 H) ' 

Aniline. Zinc-ethyle. Zinc-phenylirnide. Ethyle hydiide. 

When the zinc-phenylimide is treated with water, of course aniline is 
reproduced. 

When diethylamine is treated with zinc-ethyle — 

2N(C 2 H 5 ) 2 H + (C 2 H 5 ) 2 Zn = N 2 (C 2 H 5 ) 4 Zn + 2(C 2 H 5 .H) . 

Diethylamine. Diethylzincamine. 

When zincamide is heated above 400° F., it is decomposed into am- 
monia and zinc nitride (N 2 Zn 3 ), which represents 2 atoms of ammonia, 
in which the 6 atoms of hydrogen are replaced by zinc — 

3(NH 2 ) 2 Zn {Zincamide) = N 2 Zn 3 (Zinc nitride) + 4NH 3 . 

The zinc nitride is a grey powder, which is unaffected by a red heat 
if air be excluded. If it be moistened with water it becomes red hot, 
being decomposed with great violence, according to the equation — 

¥ 2 Zn 3 + 6H 2 = 2NH 3 + 3Zn(OH) 2 . 

It might be anticipated that if the amides be truly formed after the 
ammonia-type, they should behave towards zinc-ethyle in the same manner 
as ammonia and aniline. 

By heating oxamide with zinc-ethyle, 2 of its atoms of hydrogen may 
be replaced by zinc — 

X 2 H 4 .C 2 2 + Zn(C 2 H 5 ) 2 = lS T 2 H 2 Zn.C 2 2 + 2(C 2 H 5 .H). 

Oxamide. Zinc-oxamide. 

In a similar manner acetamide (NH 2 C 2 H 3 0) is converted into zinc- 
acetamide N 2 H 2 Zn(C 2 H 3 0) 2 . These bodies are reconverted into their 
corresponding amides and zinc oxide, when treated with water. 

Derivatives of the Alcohols. 

397. Chloroform. — Among the useful substances prepared from members 
of the alcohol series, chloroform (CHC1 3 ) occupies a prominent position. 

It is prepared by distilling 1 part of alcohol (sp. gr. -834) with 10 parts 
of chloride of lime, and 40 parts of water, at 65° C., until about 1| part 
has passed over ; the distilled liquid, consisting chiefly of water and 
chloroform, separates into two layers, the heavier being chloroform 
(sp. gr. 1*5). The upper aqueous layer having been drawn off by a 



554 CHLOROFORM. 

siphon, the chloroform is shaken with oil of vitriol to remove certain 
volatile oils, which have distilled over with it, and as soon as it has 
risen to the surface of the oil of vitriol, it is drawn off and rectified by 
distillation, until it boils regularly at 61° C. (142° R). 

The chemical change involved in the preparation of chloroform is 
expressed in the equation 2C 2 H 6 + 4Ca(C10) 2 = 2CHC1 3 {chloroform) 
+ Ca(CH0 2 ) 2 {calcium formiate) + CaCl 2 + 2Ca(HO) 2 + 2H 2 0. 

Chloroform is remarkable for its very fragrant odour, and for the power 
of its vapour to produce insensibility to pain, for which purpose it is 
often used in surgical operations. This property is not peculiar to chloro- 
form, but is possessed in different degrees by most other liquids of power- 
ful ethereal odour, such as ordinary ether, carbon disulphide, carbon 
tetrachloride, &c. Chloroform is also used for dissolving caoutchouc, 
which it takes up more readily and abundantly than any other liquid, 
and is employed for extracting the poisonous alkaloids (particularly 
strychnine), when mixed with organic matters. The name chloroform 
has been conferred upon this substance on the supposition that it con- 
tained the radical of formic acid (formyle CH), and it is sometimes styled 
the trichloride of formyle. This belief is encouraged by its behaviour 
with an alcoholic solution of potash, when it yields potassium formiate 
and potassium chloride — 

CHC1 3 + 4KHO = KCH0 2 + 3KC1 + 2H 2 0. 

Chloroform. Potassium formiate. 

But the processes by which it may be formed would lead us to regard it 
as a substitution-product from marsh gas (methyle hydride, CH 3 .H). If 
marsh gas be diluted with an equal volume of carbonic acid gas and to 1 
volume of this mixture at least 1 J volume of chlorine be added, chloro- 
form is slowly produced; CH 4 + Cl 6 = 3HC1 + CHG 3 . Chloroform is also 
formed by the action of chlorine upon methyle chloride — 

CH 3 C1 + Cl 4 = CHC1 3 + 2HC1 . 

Wood-spirit (methyle hydrate) may be employed instead of alcohol for 
the preparation of chloroform. 

If chloroform be distilled in a current of chlorine, it is converted into 
carbon tetrachloride, CHC1 3 + Cl 2 = CC1 4 + HC1. When chloroform is 
heated with potassium amalgam, acetylene (C 2 H 2 ) is disengaged, which is 
polymeric with the hypothetical radical formyle CH. 

On heating chloroform with aniline (phenylamine) and alcoholic solu- 
tion of potash, phenyle-carbamine (C 6 H 5 NC) is produced, and may be 
recognised by its most remarkable odour, which permits the detection of a 
very minute quantity of chloroform — 

HCC1 3 + H 2 jS t C 6 H 5 + 3KOH = C 6 H 5 NC + 3KC1 + 3H 2 0. 

Chloroform. Phenylamine. Phenyle-carbamine. 

When chloroform is heated with sodium ethylate, it yields tribasic formic 
ether — 

HCC1 3 + 3NaOC 2 H 5 = 3KaCl + (CH)0 3 (C,H 5 ) 3 . 

Bromoform (CHBr 3 ) and Iodoform (CHI 3 ) have no j)ractical interest. 

The production of iodoform is sometimes turned to account in testing 
for alcohol ; a little potash being dissolved in the suspected liquid, and 
some iodine added; on heating the solution, the iodoform is recognised 



CHLORAL. 555 

by its odour, resembling chloroform ; if there be much iodoform it forms 
a yellow precipitate. Iodoform is sometimes used in medicine. 

Chloral (C 2 HC1 3 0), which has been mentioned as resulting from the 
action of chlorine upon alcohol, may be regarded as aldehyde (C 2 H 4 0), in 
which 3 atoms of hydrogen are replaced by chlorine. 

It is prepared by passing thoroughly dried chlorine into absolute 
alcohol, which must be placed in a vessel surrounded by cold water at 
the commencement, because the absorption of chlorine is attended by 
great evolution of heat. The passage of chlorine is continued for many 
hours, and when the absorption takes place slowly, the alcohol is gradu- 
ally heated to boiling, the chlorine being still passed in until the liquid 
refuses to absorb it. The principal reaction is C 2 H 6 (alcohol) + Cl 8 
= C 2 HC1 3 (chloral) + 5TLC1.* But a secondary reaction takes place 
between the hydrochloric acid and the alcohol; (C 2 H 5 )HO (alcohol) 
+ HC1 = H 2 + (C 2 H 5 )C1 (hydrochloric ether). The water thus formed 
combines with the chloral, forming a heavy oily liquid which solidifies 
on standing to a white crystalline mass of chloral hydrate, C 2 HC1 3 0.H 2 0. 
To obtain chloral itself, this must be distilled with twice its volume of 
oil of vitriol to remove the water, and with quicklime to remove the 
hydrochloric acid. 

In the preparation of chloral hydrate on the large scale, chlorine is 
passed into alcohol of at least 96 per cent, for twelve or fourteen days. 
The crude product is heated with an equal weight of strong sulphuric 
acid in copper vessels lined with lead. Hydrochloric acid escapes at first, 
and the chloral distils over at about 212° F. The distillate is rectified, 
and mixed with water in glass flasks, when chloral hydrate is formed, 
which is poured into large porcelain basins where it solidifies. 

Chloral is a colourless liquid, with a peculiar pungent odour exciting 
to tears. Its sp. gr. is 1*5, and it boils at 201° F. It makes a greasy 
mark on paper, and mixes with water, alcohol, and ether. 

When mixed with a small quantity of water, combination takes place, 
with evolution of heat, and the crystallised hydrate is produced. Ex- 
posed to moist air, it absorbs water and forms the hydrate. The chloral 
hydrate itself readily absorbs water from the air; it may be sublimed 
without decomposition, though its vapour undergoes dissociation. 

When kept, chloral surfers a change somewhat resembling that of alde- 
hyde, becoming an opaque white mass, insoluble chloral, insoluble in 
water, alcohol, and ether, and reconvertible into liquid chloral by distilla- 
tion. Left in contact with water, it becomes gradually converted into 
chloral hydrate. Chloral is decomposed by solution of potash ; C 2 HC1 3 
(chloral) + KHO = KCH0 2 (potassium formiate) + CHC1 3 (chloroform). 

Chloral hydrate has been lately much used medicinally for procuring 
sleep. The distillation of starch or sugar with hydrochloric acid and 
manganese dioxide furnishes chloral together with other products. 

If aldehyde be cooled, saturated with chlorine, heated to 100° C. and again saturated 
with chlorine at that temperature, it is con-verted into croton- chloral — 

2C 2 H 4 (Aldehyde) + Cl 6 = C 4 H 3 C1 3 (Croton-chloral) + H 2 + 3HC1. 

Croton-chloral is derived from C 4 H 6 croton-aldehydc (crotonic acid, C 4 H 6 2 , is obtained 

* An intermediate compound of chloral and alcohol, C 2 HC1 3 0.C 2 H 6 0, also appears to be 
formed._ It is a solid crystalline body, fusing at 115° F., boiling at 234° F., and difficultly 
soluble in water, which distinguishes it from chloral hydrate. Heat decomposes it into 
chloral and alcohol. 



556 PERFUME-ETHERS — ALDEHYDES. 

rom croton oil). Croton-chloral is an oily liquid of a pungent smell, boiling at 164° 
C. It combines with water to form a hydrate which dissolves in hot water, and 
crystallises, on cooling, in plates which have a very irritating odour. It has been 
used in medicine. 

398. Perfume ethers — Fruit essences. — Certain of the compound ethers, 
formed by the acids of the acetic series, are employed in perfumery and 
confectionery. 

Thus, ethyle butyrate or butyric ether (C 2 H 5 .C 4 H 7 2 ), prepared "by dis- 
tilling potassium butyrate with alcohol and sulphuric acid, has a decided 
flavour, of pine apples. Formic ether is used for flavouring rum and arrack. 
Amyle acetate (C 5 H u .C 2 H 3 2 ) has a very strong resemblance in taste and 
smell to the jargonelle pear ; it is obtained by distilling fousel oil (amyle 
hydrate) with sodium acetate and sulphuric acid. 

The amyle valerianate, which has the flavour of apples, and is known 
as apple oil, is obtained by distilling fousel oil with sulphuric acid and 
potassium dichromate, when the chromic acid of the latter oxidises one 
portion of the amyle hydrate (C 5 H n .HO), converting it into valerianic 
acid C 5 H 10 O 2 ), which then forms amyle valerianate (C 5 H u .C 5 H 9 2 ). 

399. Aldehydes — Vinic or acetic aldehyde. — It has been already 
noticed (p. 499) that a considerable loss of alcohol has occasionally taken 
place in the manufacture of vinegar, in consequence of the formation of 
aldehyde (C 2 H 4 0) instead of acetic acid (C 2 H 4 2 ) by partial oxidation 
of the alcohol. In order to prepare aldehyde in quantity, alcohol is dis- 
tilled with sulphuric acid and manganese dioxide, or with sulphuric 
acid and potassium dichromate, or it may be oxidised by chlorine in the 
presence of water. 

Three parts of bichromate of potash, in crystals free from powder, are placed in a 
flask or retort surrounded by ice (or by a mixture of sulphate of soda crystals with 
half their weight of hydrochloric acid), and a mixture of 2 parts ordinary alcohol, 4 
parts sulphuric acid, and 12 parts of water, also previously cooled in ice, is added. 
The flask or retort is then connected with a Liebig's condenser containing iced water, 
and the refrigerating mixture removed, when the whole of the aldehyde will generally 
be distilled over by the heat attending the reaction. 

In these processes the alcohol is oxidised according to the equation — 

C 2 H 6 (Alcohol) + = C 2 H 4 (Aldehyde) + H 2 . 

In the first process the oxygen is derived from the manganese dioxide, 
leaving manganous sulphate (MnO.S0 3 ) in the retort ; in the second 
process, the dichromate furnishes the oxygen, chromium sulphate 
Cr 2 (S0 4 ) 3 being formed. As might be expected, a portion of the alcohol 
is oxidised to a higher degree, and converted into acetic acid (C 2 H 4 2 ), 
so that some acetic ether comes over together with the aldehyde. Another 
product, acetal, is also found in the distillate, which has the composition 
C 6 H 14 2 , and may be regarded as resulting from the union of ether, formed 
by a secondary action of the sulphuric acid upon the alcohol, with aldehyde 
(((; 2 H 5 ) 2 O.C 2 H 4 0). 

By redistilling the aldehyde with an equal weight of fused calcium chloride in a 
gently heated water-bath, it may be freed from most of the water and alcohol, which 
are left behind in the retort, the boiling-point of aldehyde being only 67° "8 F. After 
rectification, it may be separated from the acetic ether and acetal, by taking advan- 
tage of its property of combining with ammonia to form a compound which is 
insoluble in ether ; the rectified aldehyde is mixed with twice its volume of ether, 
placed in a bottle surrounded by ice, and saturated with gaseous ammonia (page 125), 
when white needle-like crystals of aldehyde ammonia (NH 3 .C 2 H 4 0) are deposited. 



ALDEHYDE. 



557 



By distilling this compound with diluted sulphuric acid, and condensing the vapour 
in a thoroughly cooled receiver, pure aldehyde is obtained, from which the last por- 
tions of water may be removed by standing over fused calcium chloride and a final 
distillation. 

Aldehyde may be recognised by its peculiar acrid odour, which affects 
the eyes, as well as by its volatility and inflammability. It absorbs 
oxygen from air even at the ordinary temperature, and is gradually con- 
verted into acetic acid. Its attraction for oxygen enables it to reduce the 
salts of silver to the metallic state, and a characteristic test for aldehyde 
consists in adding a little silver nitrate and a trace of ammonia ; on 
heating, the silver is deposited as a mirror on the sides of the test-tube. 
In contact with potassium hydrate, aldehyde undergoes decomposition, 
yielding a brown substance (resin of aldehyde) and a solution of acetate 
and formiate of potassium. By distilling a mixture of these two salts, alde- 
hyde may be reproduced — 



KC 2 H 3 0. 2 

Potassium acetate. 



+ KCH0 2 = 

Potassium formiate. 



K 9 C0, + 



C 2 H 4 

Aldehyde. 



These reactions lend some support to the opinion, that aldehyde should 
be represented as being framed upon the model of a molecule of hydrogen 
(HH), in which the place of 1 atom of hydrogen is occupied by acetyle 
(C 2 H 3 0), the hypothetical radical of acetic acid. For if potassium 
formiate be distilled with caustic potash, it yields potassium carbonate 
and 2 atoms of hydrogen, KCH0 2 + KHO = K 2 C0 3 + HH ; and if potassium 
acetate be employed instead of the hydrate, aldehyde is obtained instead 
of hydrogen, KCH0 2 4- K(C 2 H 3 0)0 = K 2 C0 3 + (C 2 H 3 0)H. 

On this view it is easy to explain the tendency of aldehyde to undergo 
oxidation, forming acetic acid, just as hydrogen is converted into water 
by oxidation. 



Type. — Molecule of water, H 2 
Acetic acid, (C 2 H 3 0)HO 



Type. — Molecule of hydrogen, H.H 
Aldehyde, C 2 H 3 O.H 

As might be anticipated, it is found that when vapour of aldehyde is 
passed over heated caustic potash (mixed with lime) it yields potassium 
acetate and hydrogen, C 2 H 3 O.H + KHO = H.H + K(C 2 H 3 0)0. 

By the action of potassium, the atom of hydrogen may be displaced 
from the aldehyde, and the compound (C 2 H 3 0)K obtained. 

In contact with water and sodium amalgam, aldehyde combines with 
the nascent hydrogen, and produces alcohol. Chlorine displaces three- 
fourths of the hydrogen from aldehyde, producing chloral, C 2 C1 3 H0, 
wdiich has been already noticed as yielding chloroform when acted on by 
alkalies. 

Perfectly pure aldehyde can be kept unchanged ; but in the presence of a very 
small quantity of hydrochloric or sulphurous acid, or carbon oxychloride, it undergoes 
a polymeric transformation into paraldehyde (or elaldehyde), C 6 H l2 3 , which crystallises 
in prisms when cooled to 10° C, and boils at a much higher temperature than aldehyde, 
into which it maybe reconverted by distillation with sulphuric or hydrochloric acid. 
If aldehyde be cooled in a freezing mixture, and a few bubbles of hydrochloric or 
sulphurous acid passed in, metaldehyde crystallises out. This body may be recon- 
verted into aldehvde by distillation with diluted sulphuric acid, or by heating in a 
sealed tube to 240° F. 

PC1 5 converts aldehyde into ethylidene dichloride C 2 H 4 C1 2 , which is isomeric with 
Dutch liquid, but not identical with it. 

In contact with moderately strong hydrochloric acid, aldehyde gradually becomes 
converted into aldol C 4 H 8 2 , which possesses some of the chemical properties both of 



558 ALDEHYDES. 

an aldehyde and an alcohol. The action appears to take place in two stages ; in the first, 
the HC1 converts the aldehyde into a chlorhydrin ; CH 3 .CH0 + HC1 = CH 3 .CH(0H)C1 ; 
in the second, the chlorhydrin is acted on by the aldehyde, forming aldol and hydro- 
chloric acid ; CH 3 .CH(OH)Cl + CH 3 .CHO=:HCl + CH 3 .CH(OH).CH 2 .CHO. 

When aldehyde is treated with a saturated solution of sodium bisul- 
phite (NaHSOg), it forms a crystalline compound which is soluble in 
water, but insoluble in the saline solution, and contains the elements of 2 
molecules of the aldehyde and 1 molecule of the bisulphite. 

If the view above referred to be correct, which represents aldehyde as 
the hydride of acetyle (the radical of acetic acid), each of the acids 
belonging to the acetic series would be expected to have a corresponding 
aldehyde. Accordingly, just as calcium acetate, when distilled with 
calcium formiate, yields acetic aldehyde, so valerianic, cenanthic, and 
caprylic aldehydes may be obtained by distilling the corresponding calcium 
salts with calcium formiate. 

The chief aldehydes of this series which have at present been examined 
are — 



Acetic aldehyde, . 


. C 2 H 4 0* 


Caprylic aldehyde, . 


. C 8 H 16 


Propionic aldehyde, 


. C 3 H 6 


Rutic aldehyde, 


• C 10 H 20 O 


Butyric aldehyde, . 


. C 4 H 8 


Euodic aldehyde, 


• C u H M 


Valeric aldehyde, . 


. C 5 H 10 O 


Laurie aldehyde, 


• C 12 H 24 


(Enanthic aldehyde, 


. C 7 H 14 







The radicals corresponding to acetyle, which may be regarded as asso- 
ciated with hydrogen in these aldehydes, have not, for the most part, been 
isolated ; a substance having the same composition as butyryle (C 4 H 7 0), 
the supposed radical of butyric acid (C 4 H 8 2 ), has, however, been obtained 
from that acid by an indirect process. 

Acetic, propionic, and butyric aldehydes have been found among the 
products of the oxidising action of a mixture of manganese dioxide and 
sulphuric acid upon fibrine, albumen, and caseine. 

Valeric aldehyde is obtained, like acetic aldehyde, by distilling the 
corresponding alcohol (amyle-alcohol, C 5 H 12 0) with sulphuric acid and 
potassium dichromate. 

Capric (rutic), euodic, and lauric aldehydes arc found in essential oil of 
rue. The higher aldehydes of the series are not so easily oxidised as those 
containing a lower number of carbon atoms. 

When an aldehyde is heated with one of the bases derived from 
ammonia by the substitution of an alcohol-radical for 1 atom of hydro- 
gen, the other 2 atoms of hydrogen of the ammonia are replaced by the 
diatomic hydrocarbon of the aldehyde ; thus — 

2NH 2 C 6 H U + 2C 7 H 14 = 2H 2 + N 2 (C 5 H n ). 2 (C 7 H I4 ) 2 ". 

. , . 03nantliic Di-oenanthvlene-di- 

Amylamine. aldehyde. amylamine. 

This reaction has been recommended for the determination of the re- 
placeable (or typical) hydrogen in organic bases. 

400. Acetones or Ketones. — If the calcium salts of the acids of the 
acetic series, instead of being distilled with calcium formiate, as for the 
preparation of the aldehydes, be distilled alone, or with quicklime, in an 

* It will be remarked that these aldehydes are polymeric with the compound ethers 
formed by their acids ; thus, acetic aldehyde is polymeric with acetic ether, for — 

2C 2 H 4 = C 2 H 5 .C. 2 H 3 2 , 
but the sp. gr. of aldehyde vapour (1*53) is only half that of acetic ether vapour (3*06). 



ACETONES OR KETONES. 559 

iron tube placed in a combustion furnace (page 84) and heated gradually 
from back to front, a series of homologous products is obtained, each of 
which is isomeric with the aldehyde of the series next below it in the table, 
though totally different from that aldehyde in properties. 

Thus, by distilling calcium acetate with lime, the liquid acetone or 
pyro-acetic spirit (C 3 H 6 0) is obtained, which has been already noticed 
among the products of the distillation of wood — 

Ca(C 2 H 3 2 ) 2 (Calcium acetate) = CaC0 3 + C 3 H 6 (Acetone). 

The ketones bear the same relation to the secondary monatomic alcohols 
(p. 517) as the aldehydes bear to the primary alcohols, and may be ob- 
tained from them by oxidation in a similar manner. Propyle alcohol, 
when oxidised, yields propyle aldehyde — 

C 2 H 5 .H 2 .OH + = C 2 H 5 .H.O + H 2 

"c c" 

Propyle-alcohol. Propyle-aldehyde. 

But isopropyle-alcohol, which is a secondary alcohol, yields acetone — 
CH 3 .CH 3 .H.OH + = CH s -CH- 8 + H 2 0. 



C 

Isopropyle-alcohol. 

When the ketones are treated with water and sodium- amalgam (to yield 
nascent hydrogen), they give secondary alcohols, whilst the aldehydes give 
primary alcohols. 

The ketones form crystalline compounds with acid sodium sulphite, but 
do not reduce silver-nitrate like the aldehydes. 

By distilling a mixture of two salts of acids of the acetic series, double 
ketones are obtained. Thus, if potassium acetate be distilled with potas- 
sium propionate, acetone-propione is obtained — 

KC 2 H 3 2 + KC 3 H 5 2 - C 4 H 8 + K 2 C0 3 . 

Posassium acetate. Potassium propionate. Acetone-propione. 

The constitution of a ketone may be inferred from the products of its 
oxidation by chromic acid or by potassium hydrate ; thus acetone yields 
acetic (C 2 H 4 2 ) acid and formic (CH0 2 ), ethyl-amyle ketone yields valeric 
(C 5 H 10 O 2 ), and propionic (C 3 H 6 2 ). 

It will be seen that the ketones form a homologous series of which the odd 
members are single ketones, and the even members are double ketones — 



Acetone, 



C 3 H 6 
C 4 H 8 
C 5 H 10 O 
C 6 H 12 
C 7 H 14 



Acetone-propione, . 
Propione, 

Propione-butyrone, 
Butyrone, 
and so on. 

Acetone may be obtained by the action of zinc-methyle on carbon oxy- 
chloride — 

COCl 2 + Zn(CH 3 ) 2 = ZnCl 2 + CO(CH 3 ) 2 

Carbon oxychloride. Zinc-methyle. Acetone. 

Acetone may also be prepared by distilling sugar with eight times its 
weight of quicklime, when it is accompanied by another liquid, metacetone, 
C 6 H 10 O, which differs from acetone in being insoluble in water. 



560 OIL OF BITTER ALMONDS AN ALDEHYDE. 

401. The description above given of the properties of aldehyde will 
have recalled those of some of the essential oils containing oxygen. Thus 
essential oil of bitter almonds (CyHgO), when exposed to air, absorbs 
oxygen, and is converted into benzoic acid (C 7 H 6 2 ), just as aldehyde 
(C 2 H 4 0) passes into acetic acid (C 2 H 4 2 ). Moreover, oil of bitter almonds 
forms a crystalline compound with sodium disulphite, similar to that 
formed by aldehyde, and its conversion into this compound is sometimes 
resorted to in order to obtain the pure oil. 

In constitution, also, oil of bitter almonds (benzoyle hydride, C 7 H 5 O.H) 
closely resembles aldehyde (acetyle hydride, C 2 H 3 O.H), and just as the 
latter may be obtained by distilling potassium acetate with potassium 
f ormiate, so benzoic aldehyde (oil of bitter almonds) may be obtained from 
potassium benzoate — 

KC 7 H 5 2 + KCH0 2 = K a CO s + C 7 H 5 O.H 

Potassium benzoate. Potassium formiate. Benzoic aldehyde. 

Oil of bitter almonds is produced, together with some aldehydes of the 
acetic series of acids (page 558), when certain albuminous bodies are oxi- 
dised by sulphuric acid and manganese dioxide. 

When benzoic aldehyde is acted on by an alcoholic solution of potash, 
an oily liquid is obtained, which stands in the same relation to benzoic 
aldehyde as alcohol bears to acetic aldehyde — 

2(C 7 H 5 O.H) + KHO = K(C 7 H 5 0)0 + C 7 H 8 

Benzoic aldehyde. Potassium benzoate. Benzoic alcohol. 

The conversion of bitter almond oil into benzoic alcohol may also be 
effected by the action of water and sodium amalgam (to furnish nascent 
hydrogen) ; whereas, by treatment with zinc and hydrochloric acid, it is 
converted into liydrobenzoine (C 7 H 7 0). 

The hydrochloric ether of benzoic alcohol, C 7 H 7 C1, is sometimes called 
benzyle chloride, the radical benzyle, C 7 H 7 , being supposed to have the 
same relation to the benzoic series as ethyle has to the acetic series. By 
the action of ammonia upon benzyle chloride, benzylamine, NH 2 (C 7 H 7 ), 
andtri-benzylaminc, N(C 7 H 7 ) S , have been obtained; the former is isomeric 
with toluidine, but is by no means identical with it; for benzylamine is 
a liquid having basic properties far more powerful than those of toluidine, 
and it is very readily soluble in water, which dissolves but little of the 
latter base. 

By distilling benzyle chloride with potassium cyanide, phenylaceto- 
nitrile, C 6 H 5 .CH 2 .CN, is obtained. This liquid forms the principal part 
of the oil of cress and oil of nasturtium, 

The benzoic acetone or benzone (C 13 H 10 O) has been obtained by the 
distillation of calcium benzoate. It is often called benzoplienone, being 
regarded as an association of benzoyle with phenyle, C 7 H 5 O.C 6 H 5 ; for 
when distilled with potash, it yields potassium benzoate and benzene 
(phenyle hydride) ; C 7 H 5 O.C 6 H 5 + KHO = K(C 7 H 5 0)0 + C 6 H 5 .H 

Benzophenone. Potassium benzoate. Benzene. 

Oil of cinnamon (page 482), or cinnamyle hydride (C 9 H 7 O.H), is the 
aldehyde of cinnamic acid (C 9 H 8 2 ) ; and essential oil of cummin contains 
the aldehyde (C 10 H n O.H) of cuminic acid (C 10 H 12 O 2 ), and yields cuminic 
alcohol (C 10 H 14 O) when treated with alcoholic solution of potash. Oil of 
spiraea or salicyle hydride (C 7 H 5 2 .H) is the aldehyde of salicylic acid 
(C 7 H 6 3 ). Anisyle hydride (C 8 H 7 2 .H), obtained by the oxidation of 



POLYATOMIC ALCOHOLS. 561 

oil of aniseed, is the aldehyde of anisic acid (C 8 H 8 3 ), and of anisic 
alcohol (C 8 H 10 O). These aldehydes allow their associated atom of hydro- 
gen to be displaced by chlorine more readily than the aldehydes of the 
acetic series, to form chlorides of their respective radicals (page 481). 

Glycol — Polyatomic Alcohols. 

402. It has been already shown (page 530) that alcohol may be con- 
veniently regarded as composed after the fashion of a molecule of water 
(H 2 0) in which half the hydrogen has been displaced by ethyle (C 2 H 5 ) ; 
according to this view alcohol is represented by the formula H(C 2 H 5 )0 ; 
and it is a monatomic alcohol, for it contains the monatomic radical, 
(C 2 H 5 )'. But if, following the same plan, .a diatomic radical, such as 
ethylene (C 2 H 4 )", were to displace half the hydrogen in water, the dis- 
placement could not be effected in less than 2 molecules of water (H 4 2 ), 
and a diatomic alcohol would result. 

Glycol (C 2 H 6 2 ) is the representative of the diatomic alcohols, and may 
be regarded as 2 molecules of water, in which half the hydrogen is 
replaced by ethylene (H 2 (C 2 H 4 )"0 2 ). It is obtained by heating 50 
grammes of ethylene dibromide with 40 grammes of potassium carbonate, 
and 100 grammes of water for eighteen hours in a flask provided with 
a reversed condenser (fig. 290); C 2 H 4 Br 2 + K 2 C0 3 + H 2 = C 2 H 4 (OH) 2 
+ 2KBr + C0 2 . 

Glycol was originally obtained by the action of ethene di-iodide (formed 
by the absorption of oleflant gas by iodine) upon silver acetate — 

2AgC 2 H 3 2 + C 2 H 4 I 2 = 2AgI + C 2 H 4 (C 2 H 3 2 ) 2 

Silver acetate. Ethene di-iodide . " Glycol diacetate. 

The glycol diacetate thus formed corresponds to the acetic ether 
((C 2 H 5 )C 2 H 3 2 ) derived from common alcohol ; but since ethene is 
diatomic, it displaces the hydrogen in 2 molecules of acetic acid. When 
the result of this action is distilled, the glycol diacetate passes over 
as a colourless liquid, which sinks in water, and boils at 365° F. 
(197°C.).* 

Glycol can be obtained from the diacetate by digesting it with potash 
for some time at 360° F., and distilling, when the glycol passes over, its 
boiling-point being 387° F. It is a colourless liquid, having a sweet taste, 
whence it derives its name (yXvKvs, sweet). Like common alcohol, it 
mixes with water in all proportions, and may be distilled without decom- 
position. It also gives an inflammable vapour, and has never been frozen ; 
but, unlike alcohol, it is heavier than water (sp. gr. 1*125), and does not 
mix with ether, though alcohol dissolves it readily. 

The action of hydrochloric acid upon glycol does not perfectly corre- 
spond with its action upon common alcohol, for instead of yielding 
ethene dichloride, it gives a compound of hydrochloric acid with ethene 
oxide; C 2 H 4 (OH) 2 + HC1 = C 2 H 4 (0H)C1 + H 2 0. 

Glycol. Chlorhydrine of glycol. 

By decomposing this compound with potash, the ethene oxide (C 2 H 4 )"0 
is obtained, as a colourless liquid, which boils at 56° F., and is, therefore, 

* A liquid isomeric with binacetate of glycol, but boiling at 336° F. , is obtained by heat- 
ing aldehyle in a sealed tube with acetic anhydride. 

2 N 



562 GLYCOL. 

not identical with aldehyde (which boils at 68° F.), though it has the 
same composition. It is obvious that glycol might be represented as 
(C 2 H 4 )".H 2 2 , ethene hydrate, and this view is favoured by the cir- 
cumstance that glycol may be formed by heating ethene oxide with water 
in a sealed tube : but, on the other hand, when glycol is treated with zinc 
chloride, to dehydrate it, ordinary aldehyde (C 2 H 4 0), and not the ethene 
oxide, is produced. 

By the action of phosphoric chloride upon glycol, the ethene dichloride, 
or Dutch liquid, is obtained — 



C 2 H 4 (OH) 2 + 2PC1 5 = (C 2 H 4 )C1 2 + 2HC1 + 2POC1 



It will be observed that this equation is the exact counterpart of 
that which represents the action of phosphoric chloride upon water, 
substituting diatomic ethene for monatomic hydrogen— 

H 2 (OH) 2 + 2PC1 5 = (H 2 )"C1 2 + 2HC1 + 2P0C1 3 . 

Sodium acts upon glycol in the same manner as upon ordinary alcohol, 
but in consequence of the diatomic character of glycol, the reaction 
takes place in two stages, producing, successively, mono-sodium glycol, 
HNa(C 2 H 4 )"0 2 , and di-sodium glycol, Na 2 (C 2 H 4 )"0 2 , both which are 
solid. 

When glycol is exposed to the action of oxygen in the presence of 
platinum-black, or when it is cautiously oxidised with nitric acid, it 
becomes converted into glycolic acid, C 2 H 4 3 , which bears the same rela- 
tion to it as acetic acid bears to common alcohol, as will be evident from 
the following equations : * — 

C 2 H 5 OH -t- 2 = (C 2 H 3 0)OH + H 2 

Alcohol. Acetic acid. 

C 2 H 4 (OH) 2 + 2 = (C 2 H 2 0)(OH) 2 + H 2 0, 

Glycol. Glycolic acid. 

in which the change consists, in both cases, in the substitution of for 
H 2 in the radical of the alcohol, acetic acid being formed upon the type 
of a molecule of water (H 2 0) in which H is replaced by C 2 H 3 0, and gly- 
colic acid upon the type of 2 molecules (H 4 2 ), in which H 2 are replaced 
by C 2 H 2 0. If the oxidation with nitric acid be carried farther, the 
remainder of the hydrogen in this last radical is replaced by oxygen, and 
oxalic acid is produced — 

(C 2 H 2 0)(OH) 2 + 2 = (C 2 2 )(OH) 2 + H 2 0. 

Glycolic acid. Oxalic acid. 

By the action of nascent hydrogen upon oxalic acid, the in the 
radical may be again displaced by H 2 , so that glycolic acid is repro- 
duced. 

Glycolic acid forms a syrupy liquid which resembles lactic acid, but is 
distinguished from it by giving a precipitate with lead acetate. Unlike 
oxalic acid, glycolic is a monobasic acid, only 1 atom of its hydrogen 
being replaceable by a • metal. Glycolic acid is found together with 
oxalic acid among the products of the action of nitric acid upon alcohol 

* The aldehyde of glycol, glyoxal, C. 2 H 2 2 , is found among the products of the decom- 
position of nitrous ether in contact with water. 



LACTIC SERIES OF ACIDS. 



563 



in the preparation of mercuric fulminate, which is easily accounted for 
by the connection between alcohol and ethylene, which is best exhibited 
by writing the formula of alcohol (C 2 H 4 ).H 2 0. 

Glycolic acid is the first member of a series of homologous acids, of 
which the most important is lactic acid, these acids standing in the same 
relation to the glycols in which the members of the acetic series stand to 
the alcohols. 

Lactic Series of Acids. 



Name. 


Formula. 


Source. 


Glycolic acid, 
Lactic acid, . 
Butylactic acid, . 

Valerolactic acid, 

Leucic acid, . . 


C 2 H 4 0-3 
C 3 H 6 3 
C 4 H 8 3 

C 5 Hio°3 
C 6 H 12 3 


Oxidation of glycol and of alcohol. 

Fermentation of cane and milk sugars. 

Oxidation of butyl-glycol. 
j Decomposition of bromo-valerianic 
/ acid with silver oxide. 

Action of nitric acid on leucine. 



It will be observed that these acids are intermediate, with respect to 
the number of atoms of oxygen which they contain, between the acetic 
and the oxalic series of acids; thus — 



Acetic acid, 
Glycolic „ 
Oxalic ,, 



C 2 H 4 2 
C,H 4 3 
C 2 H 2 4 



Propionic acid, 
Lactic ,, 

Malonic 



C 3 H 6 2 
C 3 H 6 3 

c 3 HA 



These three series of acids, therefore, present a relation to each other 
similar to that between the three series of alcohols, represented by — 



Yinic alcohol, 
Glycol, . 
Glycerine, 



C 2 H 6 
C 2 H 6 2 

C 3 H 8 3 



The reaction is rendered intelligible if the two acids be 



C 2 H 2 4 



Just as acetic and glycolic acids are formed by the oxidation of alcohol 
and glycol, so the oxidation of glycerine by nitric acid furnishes glyceric 
acid, C 3 H 6 4 . 

The transition from the oxalic series to the lactic series of acids has 
been effected in the case of leucic acid, which has been artificially formed 
from oxalic acid, by converting it into oxalic ether, and acting upon this 
with zinc-ethyle, when leucic ether is obtained, from which leucic acid is 
easily prepared 
thus formulated — 

Oxalic acid 

Leucic „ C 2 H 2 (C 2 H 5 ) 2 3 , 

from which it appears that, neglecting intermediate stages, the zinc 
of the zinc-ethyle removes an atom of oxygen from the oxalic acid, 
leaving ethyle in its stead, so that leucic acid may be regarded as dieth- 
oxalic acid, or oxalic acid containing two of ethyle instead of one of 
oxygen. If methyle oxalate be substituted for ethyle oxalate in this 
experiment, methyle leucate, CH 3 .C 6 H n 3 , is obtained, and when this 
is decomposed by baryta, and the barium leucate treated with sulphuric 
acid, fine crystals of leucic acid are obtained, which are readily soluble in 
water, alcohol, and ether, and sublime slowly at the ordinary tempera- 



564 POLYATOMIC ALCOHOLS. 

ture.* By the reaction between methyle iodide, methyle oxalate, 
and amalgamated zinc, dimethoxalic acid, C 2 H 2 (CH 3 ) 2 3 , has been obtained, 
which may be regarded as oxalic acid containing two of methyle in the 
place of an atom of oxygen. Dimethoxalic acid is isomeric with butylactic 
or acetonic acid (C 4 H 8 3 ); it crystallises in prisms resembling those of 
oxalic acid, which may be sublimed at 122° F., and volatilise slowly even 
at the ordinary temperature. 

From the other hydrocarbons of the olefiant gas series (page 521), glycols 
may be prepared by processes similar to that which furnishes ethene- 
glycol. Thus propene (C 3 H 6 ) yields propene-glycol, (C 3 H 6 )"(OH) 2 ; 
butene (C 4 H 8 ), bidene-glycol (C 4 H 8 )"(OH) 2 ; amylene (C 5 H 10 ), amylene- 
glycol, (C 5 H 10 )"(OH) 2 ; it is a very remarkable circumstance that the 
boiling-points and specific gravities of these liquids decrease as the 
complexity of the formula increases, which is quite contrary to ordinary 
experience ; thus amylene-glycol (C 5 H 12 2 ) has the sp. gr. 0*987, and 
boils at 351° F., whilst propylene-glycol (C 3 H 8 2 ) has the sp. gr. 1*051, 
and boils at 371° F. 

When propylene-glycol is slowly oxidised, it is converted into lactic 
acid, exactly as glycol is converted into glycolic acid — 

(C s H 6 )"(OH) 2 + 2 = (C 3 H 4 0)"(OH) 2 + H 2 0. 

Propylene-glycol. Lactic acid. 

The difference between the diatomic character of glycol and the mona- 
tomic character of ordinary alcohol, is strongly marked in their behaviour 
with the organic acids, for whilst the monatomic alcohol yields (with 
monobasic acids) only one series of compound ethers derived from one 
molecule of acid, the diatomic glycol yields two series derived respectively 
from one and two molecules of acid; thus we have glycol monacetate 
(C 2 H 4 )".HO.(C 2 H 3 0)0 and glycol diacetate (C 2 H 4 )".(C 2 H 3 0) 2 .G 2 . In 
the last series, it is not necessary that the two molecules should con- 
sist of the same acid, as may be seen in the acetobutyrate of glycol, 
(C 2 H 4 )".C 2 H 3 O.C 4 H 7 0.0 2 . 

Just as polyatomic ammonias are formed upon the type of several 
molecules of ammonia, so polyatomic alcohols may be produced by the- 
substitution of compound radicals for hydrogen in a multiple alcohol 
type. Thus, by heating glycol in a sealed tube with ethene oxide, di- 
ethene tri-alcohol, H 2 (C 2 H 4 )" 2 3 , is produced, which is formed upon the 
type of three molecules of alcohol, H 3 (C 2 H 5 ) 3 3 . In a similar manner, 
tri-ethylene tetralcohol, H 2 (C 2 H 4 ) 3 "0 4 , is formed upon the quadruple 
alcohol type, H 4 (C 2 H 5 ) 4 4 . 

It will be seen hereafter that glycerine (C 3 H 8 0^), the sweet principle 
of oils and fats, is a triatomic alcohol, formed upon the type of three 
molecules of water (H 6 3 ), in which half the hydrogen is replaced by 
the triatomic radical (C 3 H 5 )'", glyceryle, the formula of glycerine being 
H 3 (C 3 H 5 )"'0 3 or(C 8 H 5 )'"(OH) 3 ._ 

It is easy to convert a diatomic into a monatomic alcohol; for example, 
if the chlorhydrine of glycol be treated with sodium amalagam in the 
presence of water, it becomes converted into ordinary (monatomic) alco- 
hol; C 2 H 5 C10 + H 2 + Na 2 = C 2 H 6 + NaHO + NaCl . 

Chlorhydrine Alcohol 

of glycol. Alcohol. 

* It is said that this leucic acid, though closely resembling that obtained from oxalic 
ether, is not identical with it. 



WATER-TYPE VIEW OF POLYATOMIC ALCOHOLS. 565 

The relation of the alcohols to water as their primary type is here 
exhibited — 

IT 1 

Type, one molecule of water, H 2 = tt \ 

IT \ 

Vinic alcohol, C 2 H 6 = /r H V I ^ 

TT \ 

Type, two molecules of water, H 4 2 = tx 2 f 2 

Glycol, C 2 H 6 2 = (c j*^,, j 2 

H 2 V 
= H VO„ 



Type, three molecules of water, H 6 0, 



hJ 



TT \ 

Diethylene-trialcohol, C 4 H 10 O 3 = , r yA/' ( n 

(C 2 H 4 )"j 
TT ) 
Glycerine, C 3 H 8 3 = (C TlV j ° 3 

TT ) 

Type, four molecules of water, H 8 4 = tt 2 \ 4 

TT ) 

Triethylene-tetralcohol, C 6 H 14 4 = /p tt 2 \" f Qt 

The compounds formed by the action of acids upon these alcohols would 
then be represented by such formulae as the folio wiug : — 



Acetic ether, 


(W>)'l 
(c 2 h 5 )' j 


Glycol monacetate, . 


. (C 2 H 3 0)'H^ 


,, diacetate, 


(C 2 H 3 0) 2 ') 
(C 2 H 4 )"} U s 




(C 2 H 3 0)' ) 
. (C 4 H 7 0)' \0 2 


„ acetobutyrate, 




(C 2 H 4 )" ) 


Monacetine, 


C 2 H 3 0)'H 2 l 
• (C 3 H 5 )"'/ U 3 


Diacetine, 


(C 2 H 3 0) 2 H'l 
• (C 3 H 6 )'" / Us 


Triacetine, 


(C 2 H 3 0) 3 ') 



ACETIC ACID— THE EATTY ACID SEKIES. 

403. The most useful of the acids belonging to the acetic series (see 
page 519) is acetic acid itself, the preparation of which has been already 
described (page 471). 

Many of its salts are extensively employed in the arts. Aluminium 
acetate is used as a mordant by the dyer and calico-printer. Lead acetate 
or sugar of lead, Pb(C 2 H 3 2 ) 2 3Aq,, is prepared by dissolving litharge 



566 ACETONE. 

(PbO) in an excess of acetic acid, when the solution deposits prismatic 
crystals of the acetate, which are easily dissolved by water and alcohol. 

On the large scale, hot acetic acid vapour is passed through copper 
vessels with perforated shelves on which litharge is placed. 

Goulard's extract, or tribasic lead acetate, is prepared by dissolving 
litharge in solution of lead acetate ; it may be obtained in needle-like 
crystals, which have the composition Pb(C 2 H 3 2 ) 2 2PbO.H 2 0. 

Verdigris, or basic copper acetate, Cu(C 2 II 3 2 ) 2 .Cu0.6H 2 0, is pre- 
pared by piling up sheets of copper with layers of fermenting husks of 
grapes (the marc of the wine-press), when the copper oxide, formed at 
the expense of the oxygen of the air, combines with the acetic acid fur- 
nished by the oxidation of the alcohol. 

Sodium acetate dissolved in water is used in foot-warmers for railway 
carriages, on account of the continuous evolution of heat during its 
crystallisation. It is four times as effective as an equal volume of 
water. 

Acetone (C 3 H 6 0) is obtained by the destructive distillation of calcium 
acetate, Ca(C 2 H 3 2 ) 2 = CaC0 3 + C 3 H 6 0, a decomposition which possesses 
some genera] interest, since the calcium salts of the other acids of the 
acetic series yield ketones in a similar manner (see page 559). 

The acetone thus obtained is an ethereal liquid lighter than water, boil- 
ing at 133° F., and burning with a luminous flame. It is easily miscible 
with water, but separates when potassium hydrate is added, rising to the 
surface. 

Under the action of chlorine, acetic acid loses an atom of hydrogen, 
taking chlorine in its place, and forming chlor acetic acid, H.C 2 H 2 C10 2 ; * 
and if the action be promoted by sun-light, trichloracetic acid may be 
formed, H.C 2 C1 3 2 , which may be crystallised. This latter acid has a 
peculiar interest on account of its being concerned in the production of 
acetic acid from inorganic materials, which was one of the first examples 
of the actual synthesis of organic compounds. 

The synthesis of acetic acid has been effected by the action of carbon 
oxychloride upon marsh gas, when hydrochloric acid and acetic oxychloride 
are formed ; CH 4 + COCl 2 = (C 2 H 3 0)C1 (Acetic oxychloride) + HC1. ' 

When the acetic oxychloride is decomposed by water, acetic acid is pro- 
duced ; (C 2 H 3 0)C1 + H 2 = H(C 2 H 3 0)0 + HC1. 

This appears to be an example of a general method of synthesis of the 
volatile fatty acids, starting from the marsh gas hydrocarbons derived from 
them; thus, amyle hydride, C 5 H 12 , treated in a similar manner, yields 
caproic acid, HC 6 H n 2 . 

404. Anhydrides of organic acids — Acetic anhydride. — The course of 
investigation by which, of late years, much light has been thrown 
upon the true constitution of acetic acid, and therefore of many other 
organic acids, is of a very instructive character. The strongest acetic 
acid which can be prepared (see p. 471) is known as glacial acetic 
acid, from its crystallising in icy leaflets at about 55° P. This acid has 
the composition C 2 H 4 2 , and may be regarded as a molecule of water in 
which half the hydrogen is replaced by the hypothetical radical acetyle, 
C 2 H 3 0. 

When this acid is distilled with phosphorous chloride, a colourless, very 

* Dichloracetic acid, H.CHCLO.,, has also been obtained. 



ACETIC ANHYDRIDE. 567 

pungent liquid is obtained, which is commonly spoken of as acetic oxy- 
chloride, C 2 H 3 0C1— 

2H(C 2 K s O)0 + PC1 3 = HC1 + HP0 2 + 2(C 2 H 3 0)C1. 
That this acetic oxychloride (or acetyle chloride) really bears a very 
close relationship to acetic acid, is shown by the action of water, which 
acts with explosive violence and reproduces the acetic acid — 

(C 2 H 3 0)C1 + H 2 = H(C 2 H 3 0)0 + HC1. 
If potash be allowed to act upon the chloride of acetyle — 
(C 2 H s O)Cl + KHO = H(C 2 H 3 0)0 + KC1. 
But if potassium acetate (KC 2 H 3 2 ) be employed instead of potassium 
hydrate; (C 2 H 3 0)C1 + K(C 2 H 8 6)0 = C 2 H 3 O.C 2 H 3 0.0 + KC1. 

Acetic oxychloride. Potassium acetate. Acetic anhydride. 

Glacial acetic acid may be used instead of the potassium salt. 

Acetic anhydride has also been obtained by heating dry acetate of lead 
or of silver with carbon disulphicle in a sealed tube to about 326° P. for 
several hours, the tube being occasionally opened to relieve the pressure 
of the carbonic acid gas evolved — 

2Pb(C 2 H 3 0) 2 2 + CS 2 = 2PbS + C0 2 + 2(C 2 H 3 0) 2 . 

The acetic anhydride is a neutral oily liquid which may be distilled off 
in the above experiment. Its smell recalls that of acetic acid, but affects 
the eyes strongly. It sinks in water, but dissolves slowly, with evolution 
of heat and formation of acetic acid.* 

The most convincing proof that this anhydride is really formed after the 
type of a molecule of water, is obtained by acting upon the acetate of 
potash with the benzoic instead of the acetic oxychloride — 

(C r H 5 0)Cl + K(C 2 H 3 0)0 = KC1 + C 7 H 5 O.C 2 H 3 0.0, 

Benzoic Potassium Benzo-acetic 

oxychloride. acetate. anhydride. 

and the true nature of this double anhydride is seen by its conversion 
into a mixture of benzoic and acetic acids when left in contact with 
water. 

By methods similar to that employed for acetic acid,. the anhydrides of 
many other organic acids may be obtained. 

Peroxides of organic radicals. — Considerable support has been offered 
to that view of the constitution of the organic acids, which represents 
them as composed after the type of water, by the discovery of certain 
compounds which bear the same relation to the anhydride as peroxide of 
hydrogen bears to water. 

When barium dioxide is acted on by hydrochloric acid, barium chloride 
and hydric peroxide are formed — 

Ba0 2 + 2HC1 = BaCl 2 + H 2 2 . 
If barium dioxide be acted on by benzoic oxychloride (benzoyle chloride), 
the products are barium chloride and benzoic peroxide (benzoyle 
peroxide) — 

Ba0 2 + 2(C 7 H 5 0)C1 = BaCl 2 + (C 7 H 5 0) 2 2 . 

* If acetic anhydride be heated with an excess of barium dioxide, it yields barium 
acetate, carbon dioxide, and methyle gas (page 526) — 

2(C 2 H 3 0) 2 + Ba0. 2 = Ba(C. 2 H 3 2 ) 2 + 2CH 3 + 2C0 2 . 
By absorbing the carbon dioxide with potash, the pure methyle gas is easily obtained. 



568 FOKMIC ACID. 

The benzoic peroxide may be obtained in fine crystals from its ethereal 
solution, but, likehydric peroxide, it is easily decomposed at about 212° F. 
with explosive violence. By the action of alkalies it is resolved into 
benzoic acid and oxygen, just as hydric peroxide yields water and 
oxygen — 

(C 7 H 5 0) 2 2 + 2KHO = 2K(C 7 H 5 0)0 + + H 2 0. 

By acting upon acetic anhydride with barium dioxide, the acetic peroxide 
(or acetyle peroxide) is obtained — 

Ba0 2 + 2(C 2 H 3 0) 2 = Ba(C 2 H 3 2 ) 2 + (C 2 H 3 0) 2 2 

Barium acetate. Acetic peroxide. 

The acetic peroxide is an oily liquid, insoluble in water, and exploding 
with great violence when heated. It has the powerful oxidising pro- 
perties which would be expected from its chemical resemblance to hydric 
peroxide. 

Ethyle peroxide (C 2 H 5 ) 4 3 has been obtained by the action of ozone on 
ether. It forms a syrupy liquid which explodes when heated, and is 
decomposed by water, forming alcohol and hydric peroxide. 

405. Formic acid (H.CH0 2 ) is regarded with great interest by the 
chemist, from its occurring both in the animal and vegetable kingdoms, 
and from the ease with which it may be artificially obtained. This acid 
is found in the leaves of stinging-nettles, and was originally obtained by 
distilling the red ants [Formica rufa), whence it derives its name. 

It has long been prepared in laboratories by the oxidation of various 
organic substances, particularly by distilling starch with manganese 
dioxide and sulphuric acid. Another more modern process, which yields 
it more abundantly, consists in distilling oxalic acid with enough glycerine 
to cover it, when it is resolved into carbonic acid gas and formic acid ; 
H 2 C 2 4 (Oxalic acid) = HCH0 2 (Formic acid) + C0 2 . 

The glycerine appears to act by producing an unstable compound with 
the formic acid (analogous to the stearines and acetines, see p. 565) which 
is afterwards decomposed. The solution thus obtained contains 75 per 
cent, of formic acid. If dried oxalic acid be heated in the aqueous 
formic acid, and the solution allowed to crystallise, the oxalic acid retains 
the water, and when the liquid is decanted from the crystals and distilled, 
pure formic acid is obtained, and may be crystallised at a low temperature. 

But the most remarkable method of obtaining formic acid is that in 
which it is formed from inorganic materials. When formic acid is heated 
with strong sulphuric acid, it is resolved into water and carbonic oxide, 
HCH0 2 = H 2 + CO. It might, therefore, be expected to be reproducible 
by the combination of those two substances, and accordingly, if moistened 
caustic potash be heated for some hours to 212° F. in a flask filled with 
carbonic oxide, the gas is absorbed, and potassium formiate produced, from 
which the formic acid may be obtained by distillation with diluted sulphuric 
acid ; KHO + CO = KCH0 2 (Potassium formiate). 

This is a far simpler example of the synthesis of an organic compound 
from inorganic materials than that of the acetic acid above referred to, 
and since the carbonic oxide may be prepared by heating barium carbonate 
with metallic iron, this method of synthesis is quite independent of any 
organic source of carbon. Sodium ethylate, NaC 2 H 5 0, also absorbs 
carbonic oxide, forming sodium ethyl-formiate NaC(C 2 H 5 )0 2 , isomeric with 
sodium propionate, a little of this salt also being formed. 



FURFUROLE — BUTYRIC ACID. 569 

In properties, formic acid bears a great general resemblance to acetic 
acid, but has a more powerful action upon the skin when in the concen- 
trated form. It is employed in the manufacture of one of the blue colours 
derived from coal-tar. 

Furfurole or furfural (C 5 H 4 2 ), or oil of ants, accompanies the formic acid ob- 
tained by distilling amylaceous matters with manganese dioxide and sulphuric acid. 
It is prepared in quantity by distilling bran (freed from starch and gluten by steep- 
ing in a cold weak solution of potash) with half its weight of sulphuric acid (pre- 
viously diluted with an equal bulk of water), a current of steam being forced through 
the mixture ; the furfurole distils over with the water, from which it may be sepa- 
rated by fractional distillation. Furfurole has also been obtained by the action of 
steam at 100 lbs. pressure upon wood. It is a colourless oily substance, smelling of 
bitter almonds, becoming brown when exposed to the air, and but slightly soluble in 
water. Strong sulphuric acid dissolves it to a purple liquid, from which water pre- 
cipitates it unchanged. Furfurole resembles the aldehydes in its property of reducing 
silver oxide, and in forming a crystalline compound with sodium disulphite. It is 
convertible by oxidation into pyromucic acid (C 5 H 4 3 ), the acid obtained by distil- 
ling the mucic acid derived from the oxidation of gum or milk-sugar. The systematic 
name for furfurole, therefore, would be pyromucic aldehyde. 

Just as oil of bitter almonds (benzoic aldehyde), when acted on by ammonia, is 
converted into hydrobenzamide, so furfurole yields furfuramide — 

3C 7 H 6 (Oil of bitter almonds) + 2NH 3 = C 21 H 18 N 2 (Hydrobenzamide) +3H 2 
3C 5 H 4 2 (Furfurole) + 2NH 3 = C 15 H 12 X 2 3 (Furfuramide) + 3H 2 . 

And, just as hydrobenzamide, when boiled with solution of potash, yields the iso- 
meric base amarine or benzoline (C 21 H 18 ]S!" 2 ), so furfuramide when boiled with potash 
gives furf urine (C 15 H 12 N 2 3 ), which is isomeric with it. 

Butyric acid (HC 4 H 7 2 ) is found not only in rancid butter, but in 
the juice of muscular flesh, and is a frequent product of fermentation. 
Indeed, the best mode of obtaining this acid consists in exciting fermen- 
tation in sugar by contact with cheese; the liquid soon becomes acid, in 
consequence of the formation of lactic acid (the acid of sour milk), and if 
it be neutralised from time to time with chalk, this fermentation continues 
until the whole is converted into a pasty crystalline mass of calcium 
lactate Ca(C 3 H 5 3 ) 2 . The formation of lactic acid from sugar becomes 
intelligible on comparing the formula — 

1 molecule cane-sugar, C 12 H 22 O n ; 4 molecules lactic acid, C 12 H 24 12 . 

After a time the mass becomes more fluid, at the same time evolving 
bubbles of gas, which contain carbonic acid gas and hydrogen, for the 
calcium lactate is undergoing a fermentation, by which it is converted 
into butyrate — 

2Ca(C 3 H 5 3 ) 2 + H 2 = Ca(C 4 H 7 2 ) 2 + CaC0 3 + 3C0 2 + H 8 . 

Calcium lactate. Calcium butyrate. 

By distilling the butyrate with dilute hydrochloric acid, an aqueous solu- 
tion of butyric acid is obtained, and on saturating this w r ith calcium 
chloride, the acid collects as an oily layer upon the surface. It is remark- 
able for its powerful odour of rancid butter.* 

Synthetical formation of acids of the acetic series. — By a very remark 
able process of substitution, butyric acid has been derived from acetic 
acid. When sodium is heated with acetic ether, it is gradually dissolved, 
and the liquid solidifies, on cooling, to a crystalline mass containing, 

* Butyric acid and some of its homologues (as valerianic and caproic) appear to be present 
in the perspiration of the skin, and to cause the disagreeable odour of close rooms. 



570 SYNTHESIS OF ACIDS OF THE ACETIC SERIES. 

among other products, sodacetic ether, or acetic ether, in which 1 atom of 
the hydrogen has been displaced by sodium. The reaction appears to 
take place in two stages — 

(1) 3(C 2 H 5 .C 2 H 3 0.0) + Na 4 = 3(C 2 H 5 .Na.O) + Na(C 2 H 8 0) s 

Acetic ether. Sodium-alcohol. Sodium-tviacetyle. 

(2) C 2 H 5 NaO + C 2 H 5 .C 2 H 3 0.0 = C 2 H 5 .H.O + C 2 H 5 .C 2 (H 2 ¥a)0.0 

Sodium-alcohol. Acetic ether. Alcohol. Sodacetic ether. 

By digesting the sodacetic ether with ethyle iodide for several hours in 
a close vessel, at 212° F., the atom of sodium is exchanged for ethyle, and 
ethacetic ether, or butyric ether, is produced — 

C 2 H 6 .C 2 (H 2 Na)0 2 + C 2 H 5 I = Nal + C 2 H 5 .C 2 H 2 (C 2 H 6 )0 2 

Sodacetic ether. Ethyle iodide. Ethacetic or butyric ether. 

From this ether the ethacetic acid, C 2 H 3 (C 2 H 5 )0 2 , has been prepared, and 
found to be identical with butyric acid, C 4 H 8 2 . The connexion thus 
established between butyric acid and the ethyle series helps to explain 
the production of that acid in the fermentation of sugar. 

But butyric ether has also been obtained by another process. The 
substitution of sodium for hydrogen in acetic ether may extend to 2 
atoms of hydrogen, and if the disodacetie ether so produced be digested 
with methyle iodide, butyric ether is obtained — 

C 2 H5.C 2 (HNa 2 )0 2 + 2CH 3 T = 2NaI + C 2 II 5 .C 2 H(CH 3 ) 2 2 

Disodacetie ether. Methyle iodide. Dimethacetic or butyric ether. 

So that butyric acid may be regarded, according to the method by which 
it is produced, either as ethacetic acid, formed from acetic acid by the 
substitution of an atom of ethyle for one of hydrogen, or as dimethacetic 
acid, resulting from the substitution of two atoms of methyle for two of 
hydrogen. 

When disodacetie ether is acted on by ethyle iodide, it yields dieth- 
acetic ether — 

C 2 H 5 .C 2 HNa 2 2 + 2C 2 H 5 I - 2NaI + C 2 H 5 .C 2 H(C 2 H 5 ) 2 2 

Disodacetie ether. " Ethyle iodide. Diethacetic ether. 

This ether has an odour resembling peppermint, and its composition is 
the same as that of caproic ether C 2 H 5 .C 6 H n 2 ; but the diethacetic acid 
prepared from it, though isomeric with caproic acid (C 6 H 12 2 ), is not 
identical with it. 

The acid next in the series, oenanthic (HC 7 H 13 0) 2 , may be obtained 
from the ether produced by the action of amyle iodide upon sodacetic 
ether; C 2 H 5 .C 2 (H 2 Na)0 2 + C 5 H 1; I - ffal + C 2 H 5 .C 2 H 2 (C 5 H n )0 2 . 

Sodacetic ether. Amyle iodide. " Amyl-acetic ether. 

From this ether, the amyl-acetic acid, H.C 2 H 2 (C 5 H n )0 2 , which appears 
to be identical with oenanthic acid, has been obtained. 

These reactions help to explain the production of several of the alcohols 
corresponding to the acetic series of acids, during the fermentation of 
grape husks (marc of the wine-press). 

Among the products of the action of sodium and ethyle iodide upon acetic ether, is 
a liquid having the composition C 8 H 14 3 , which when distilled with barium hydrate 
yields ethylated acetone, C 3 H 5 (C o H 5 )0, isomeric with propione; C 8 H 14 3 + Ba(HO)o 
= C 5 H 10 O + O 2 H 6 O + BaCO 3 . 

Another liquid produced by the action of ethyle iodide upon disodacetie ether has 
the composition C 10 H 18 O 3 , which furnishes Methylated acetone, C 3 H 4 (C 2 H 5 ) 9 0, when 
distilled with baryta water ; Ci H 18 O 3 + Ba(HO) 2 = C 7 H 14 O + C 2 H 6 b + BaCO 3 ! 

Diethylated acetone is a liquid smelling of camphor, and boiling at 280° F. It is 



VALERIANIC ACID. 571 

isomeric with butyrone, which boils at 290° F., and with cenanthic aldehyde or 
oenan thole, which boils at 312° F. 

By treating acetic ether with sodium and methylic iodide, the corresponding 
methylated acetones may be obtained. 

Methylated acetone, C 3 H 5 (CH 3 )0, has the odour of chloroform, and is identical with 
the ethyl-acetyle, C 2 H 3 O.C 2 H 5 , obtained by the action of zinc-ethyle upon acetyle 
chloride. 

Dimethylated acetone, C 3 H 4 (CH 3 ) 2 0, has an odour of parsley. 

Valerianic acid (H.C 5 H 9 2 ) derives interest from the circumstance 
that some of its salts, particularly the zinc valerianate, are used medi- 
cinally. This acid is found in valerian root and in the berries of the 
guelder-rose. It is one cause of the peculiar odour of decaying cheese, 
and of whale and seal oils. 

Artificially, it is best obtained by distilling fousel oil (amylic alcohol, 
C 5 H 12 0) with sulphuric acid and potassium dichromate, when the oxygen 
of the chromic acid converts part of the amylic alcohol into valerianic 
acid; C 5 H 12 {Fousel oil) + 2 = C 5 H 10 O 2 ( Valerianic acid) + H 2 0. 

The distilled liquid is really a mixture of valerianic acid and amyle 
valerianate (C 5 H 11 .C 5 H 9 2 ), but when treated with caustic potash, the 
latter is decomposed, yielding fousel oil and potassium valerianate — 

C 5 H n .C 5 H 9 2 + KHO = C 6 H n .HO + K.C 5 H 9 2 

Amyle valerianate. Fousel oil. Potassium valerianate. 

Ey distilling potassium valerianate with sulphuric acid, the valerianic 
acid is obtained as an oily liquid of very remarkable odour, which recalls 
that of butyric acid. 

406. The separation of the volatile acids belonging to the acetic series 
is a problem which frequently presents itself to the chemist, and is 
effected by a very instructive process of partial saturation, founded upon 
the principle, that when a mixture containing two acids with different 
boiling-points is partially neutralised by an alkali and distilled, the more 
volatile of the two acids (i.e., that having the lower boiling-point) will 
pass over, whilst the other remains in combination with the alkali. 

In applying this method, for example, to a mixture of valerianic acid 
(boiling at 347° F.) and butyric acid (boiling at 315° F.), in unknown 
proportions, the liquid would be divided into two equal parts, one of 
which would be exactly neutralised with potash and then distilled to- 
gether with the other half. If there were just enough valerianic acid to 
combine with the potash, pure potassium valerianate would be left in the 
retort, and the more volatile butyric acid would pass over. If there were 
more valerianic acid than would be required to combine with the potash, 
the excess of that acid would distil over, together with the butyric acid, 
whilst potassium valerianate alone would be left in the retort. By distil- 
ling this salt with sulphuric acid, the pure valerianic acid would be ob- 
tained, and the separation of the rest of the valerianic from the butyric 
acid would be effected by one or two repetitions of the process. 

If the valerianic acid present in the mixture were not in sufficient 
quantity to combine with the potash added, then potassium butyrate, as 
well as valerianate, would be left in the retort, and pure butyric acid would 
distil over. By distilling the mixture of potassium valerianate and buty- 
rate with sulphuric acid, a mixture of the two acids would be obtained 
which would require a repetition of the process. Iii any case, it will be 
observed that this process must yield one of the acids in a state of purity. 



572 CHEMISTKY OF SOAP. 

The same principle applies to the separation of three or more volatile 
acids, but the process involves, of course, a greater number of distillations. 

407. Soap. — The manufacture of soap affords an excellent instance of 
a process which was in use for centuries before anything was known of 
the principles upon which it is based, for it was not till the researches of 
Chevreul were published, in 1813, that any definite ideas were entertained 
with respect to the composition of the various fats and oils from which 
soaps are made. 

The investigations of Chevreul are conspicuous among the labours 
which have contributed in so striking a manner to the rapid advancement 
of chemistry during the present century ; undertaken when the chemistry 
of organic substances had scarcely advanced beyond the dignity of an art, 
when the principles of classification were almost entirely empirical, and 
hardly any research had been published which would serve as a model, 
these researches reflect the remarkable sagacity and accuracy of their author. 

The sense of our obligation to this eminent chemist is further increased, 
when we remember that the ultimate analysis of organic substances was 
then effected by a very difficult and laborious process, whilst the doctrine 
of combining proportions was so imperfectly understood, that it could 
afford but little assistance in confirming or interpreting the results of 
analysis. 

All soaps result from the action of the alkalies upon the oils and fats. 

In the manufacture of soap, potash and soda are the only alkalies em- 
ployed, the former for soft, the latter for hard soaps. 

The fatty matters employed by the soap-maker are chiefly tallow, palm 
oil, cocoa-nut oil, and kitchen stuff, for hard soaps, and seal oil and whale 
oil for soft soaps. 

In the manufacture of hard soap, the alkali is prepared by decomposing 
or caustifying sodium carbonate (soda-ash) with slaked lime, ]Sra 2 C0 3 
+ Ca(HO) 2 = CaC0 3 + 2]STaHO, the clear solution of sodium hydrate, or 
soda-ley, being drawn off from the insoluble calcium carbonate. 

The tallow is at first boiled with a weak soda-ley,* because the soap 
which is formed is insoluble in a strong alkaline solution, and would, 
enclose and protect a quantity of undecomposed tallow; in proportion 
as the saponification proceeds, stronger leys are added, until the whole 
of the grease has disappeared. In order to separate the soap which is 
dissolved, advantage is taken of the insolubility of soap in solution of salt ; 
a quantity of common salt being thrown into the boiler, the soap rises to 
the surface, when the spent ley is drawn off from below, and the soap 
transferred to iron moulds that it may harden sufficiently to be cut up 
into bars. 

In order to understand the chemistry of this process, it is necessary to 
know that tallow contains two fatty substances, one of which stearine^ 
(C 57 H 110 O 6 ), is solid, and the other, oleine (C 57 H 104 O 6 ), liquid, the quantity 
of stearine being about thrice that of oleine. 

"When these fats are acted upon by soda, they undergo decomposition, 
furnishing stearic and oleic acids, which combine with the soda to form 
soap, whilst a peculiar sweet substance, termed glycerine, passes into 



is now sometimes made "by the action of the sodium carbonate upon the fat, thai- 
saving the expense of caustifying (Morfit's process). 
■f 2,Teap, tallow. 



ACTION OF ALKALIES ON FATS. 573 

solution; the nature of the decomposition in each case will be understood 
from the following equations : — 

C 3 H 5 .(C 18 H 35 0) 3 .03 + 3NaHO = 3Na(C 18 H 35 0)0 + C 3 H 8 3 , 

Stearine. Sodium stearate. Glycerine. 

C 3 H 5 .(C 18 H 33 0) 3 .0 3 + 3^aHO = 3Na(C 18 H 33 0)0 + C 3 H 8 3 , 

Oleine. Sodium oleate. Glycerine. 

so that the soap obtained by boiling tallow with soda is a mixture of the 
sodium stearate with about a third of its weight of sodium oleate and 
20 to 30 per cent, of water. 

Palm oil is composed chiefly of palmitine (C 51 H 98 6 ), a solid fat which 
is resolved, by boiling with soda, into sodium palmitate (palm oil soap) 
and glycerine — 

C 3 H 5 .(C 16 H 31 0) 3 3 + 3NaH0 = 3Na(C 16 H 31 0)0 + C 3 H 8 3 . 

Palmitine. Sodium palmitate. Glycerine. 

In the fish oils the predominant constituent is oleine, so that, when 
boiled with potassium hydrate, they yield potassium oleate (KC 18 H 33 2 ), 
which composes the chief part of soft soap. 

Castile soap is made from olive oil, which contains oleine and a solid fat 
known as margarine. The latter appears to be really composed of palmi- 
tine and stearine, so that the Castile soap is a mixture of oleate, palmitate, 
and stearate of sodium. 

The peculiar appearance of mottled soap is caused by the irregular dis- 
tribution of a compound of the fatty acid with oxide of iron, which 
arranges itself in veins throughout the mass. If the soap contained too 
much water, so as to render it very fluid when transferred to the moulds, 
this iron compound would settle down to the bottom, leaving the soap 
clear, so that the mottled appearance is often regarded as an indication 
that the soap does not contain an undue proportion of water ; it is imi- 
tated, however, by stirring into the pasty soap some ferrous sulphate and 
a little impure ley containing sodium sulphide, so as to produce the dark 
sulphide of iron by double decomposition.* 

In the manufacture of yellow soap, in addition to tallow and palm oil, 
a considerable proportion of common rosin (see page 476) is added to the 
soap shortly before it is finished. 

Soft soap is not separated from the water by salt like hard soap, but is 
evaporated to the required consistency. 

Transparent soaps are obtained by drying hard soap, dissolving it in hot 
spirit of wine, and pouring the strong solution into moulds after the greater 
part of the spirit has been distilled off. 

Silicated soap is a mixture of soap with silicate of soda. 

Glycerine soap is prepared by heating the fat with alkali and a little 
water to about 400° F. for two or three hours, and running the mass at 
once into moulds. It is, of course, a mixture of soap and glycerine. 

The proportion of water in soaps is very variable, some specimens con- 
taining between 70 and 80 per cent. The smallest proportion is about 30 
per cent. 

The theory of saponification, stated above, has received the strongest 
confirmation within the last few years, by the synthetic production of the 
fats from glycerine and the fatty acids formed in their saponification. 

* A soap which contains much more than 30 per cent, of water is said not to admit of 
mottling. 



574 STEAKIC AND OLEIC ACIDS. 

Preparation of the fatty acids. — All the soaps, when mixed with acids, 
undergo decomposition, their alkalies combining with the acid added, 
whilst the fatty acids separate, either in the solid form (in the case of 
stearic and palmitic acids), or as an oily liquid (in the case of oleic acid). 
Thus, if soap obtained by boiling tallow with soda be dissolved in hot 
water, and mixed with an excess of tartaric acid, an oil rises to the surface 
which concretes into a buttery mass on cooling. This mass, composed of 
stearic and oleic acids, is submitted to pressure in order to separate the 
greater part of the liquid oleic acid, and the stearic acid which is left is 
purified by crystallisation, first from alcohol, and afterwards from ether. 

Stearic acid is thus obtained in transparent colourless plates which have 
the composition HC 18 H 35 2 ; they are, of course, insoluble in water, but 
dissolve in hot alcohol, the solution being acid to test-papers. 

By repeated distillation under pressure, stearic acid is completely de- 
composed into H 2 and C0 2 , and hydrocarbons of the paraffin (C„H 2 2 ) 
and olefine C„H 2n ) series. 

All the stearates are insoluble in water except those of the alkalies, so 
that if a solution of common soap (containing sodium stearate) be mixed 
with a solution of calcium or magnesium, a stearate of calcium or mag- 
nesium is separated in the insoluble form, and it will be remembered that 
this decomposition of soap is produced by the action of hard waters 
(page 45). 

408. Candles. — Since tallow fuses at about 100° F., and stearic acid 
not below 159°, it is evident that, independently of other considerations, 
the latter would be better adapted for the manufacture of candles, for such 
candles would never soften at the ordinary atmospheric temperature in 
any climate, and would have much less tendency to gutter in consequence 
of the excessive fusion of the fuel around the base of the wick. The 
gases furnished by the destructive distillation of stearic acid in the wick 
of the candle burn with a brighter flame than those produced from tallow. 
Accordingly the manufacture of stearine (or more correctly, stearic acid) 
candles* has now become a very important and instructive branch of 
industry. 

The original method of separating the stearic acid from tallow on the 
large scale consisted in mixing melted tallow with lime and water, and 
heating the mixture for some time to 212° by passing steam through it. 

The tallow was thus converted into the insoluble stearate and oleate of 
calcium, which was drained from the solution containing the glycerine, 
and decomposed by sulphuric acid. The mixture of stearic and oleic acids 
thus obtained was cast into thin slabs, which were packed between pieces 
of cocoa-nut matting, and well squeezed in a hydraulic press, which forced 
out the oleic acid, leaving the stearic and palmitic acids in a fit state for 
the manufacture of candles. 

The separation of the solid fatty acids from tallow and other fats may 
also be effected by the action of the sulphuric acid,- a process extensively 
applied in this country to palm and cocoa-nut oils. These fats are mixed 
in copper boilers with about one-sixth of their weight of concentrated sul- 
phuric acid, and heated by steam to about 350° F. for some hours, when 
part of the glycerine is converted into sulphoglyceric acid (C 3 H 8 3 .S0 3 ), 
and the remainder is decomposed by the sulphuric acid, carbonic and sul- 

* Composite candles are made of a mixture of stearic and palmitic acids. 



DECOMPOSITION OF FATS BY SULPHURIC ACID. 575 

ptmrous acid gases being disengaged, whilst a dark-coloured mixture of 
palmitic, stearic, and oleic acid is left. A part of the oleic acid becomes 
converted in this process into elaidic acid, which has the same composition, 
but differs from oleic acid in fusing at about. 113° F., so that the amount 
of solid acid obtained by this process is much increased. This mixture is 
well washed from the adhering sulphuric and sulphoglyceric acids, and 
transferred to a copper still into which a current of steam is passed, 
which has been raised to about 600° F. by passing through hot iron pipes. 
These fatty acids could not be distilled alone without decomposition, but 
under the influence of a current of steam they pass over readily enough, 
leaving a black pitchy residue in the retort, which is employed in making- 
black sealing-wax, and for other useful purposes. 

The distilled fatty acids are broken up and pressed, between cocoa-nut 
matting to remove the oleic acid. 

One great advantage of this process, which is commonly, though incor- 
rectly, styled the saponification by sulphuric acid, is its allowing the con- 
version of the worst kinds of refuse fat into a form fit for the manufacture 
of candles ; thus the fat extracted from bones in the manufacture of glue, 
and that removed from wool in the scouring process, may be turned to 
profitable account. 

It will be remarked that in this process the palmitic, stearic, and oleic 
acids are formed from the palmitine, stearine, and oleine existing in the 
fats, by the assimilation of the elements of water and the subsequent 
separation of glycerine, just as in the ordinary process of saponification by 
means of alkalies. 

Strictly speaking, the action appears to consist of two stages ; for when 
concentrated sulphuric acid is allowed to act upon the natural fats in the 
cold, it combines with each of their ingredients, forming the acids known 
as sulphostearic, sulphopalmitic, sulpholeic, and sulphoglyceric, which 
are soluble in water, though not (with the exception of the last) in water 
containing sulphuric acid. 

The second stage consists in the decomposition of the sulpho-fatty acids 
by the high temperature in contact with steam, the sulphoglyceric acid 
having been in great measure decomposed into secondary products before 
the distillation is commenced. 

Within the last few years the extraction of the solid acids from the 
natural fats has been effected by a process known as saponification by 
steam, which allows the glycerine also to be obtained in a pure state. It 
is only necessary to subject the fat, in a distillatory apparatus, to the action 
of steam, at a temperature of about 600° F., to cause both the fatty acids 
and the glycerine to distil over ; the former may be separated as usual 
into solid and liquid portions by pressure, whilst the glycerine, which is 
obtained in aqueous solution below the layer of fatty acids, is concentrated 
by evaporation, and sent into commerce as a very sweet colourless viscid 
liquid. The saponification of palmitine, for instance, by steam, would be 
represented by the equation — 

C 3 H 5 .(C 16 H 31 2 ) 3 + 3H 2 = 3(H.C 16 H 31 2 ) + C 3 H 5 (HO) 3 . 

Palmitine. Palmitic acid. Glycerine. 

409. In the artificial formation of natural fats, this change has been 
reversed, for by heating 3 molecules of stearic, palmitic, or oleic acid with 
1 molecule of glycerine, in a sealed tube for several hours, to about 500° 



576 SYNTHESIS OF NATURAL FATS. 

F., 3 molecules of water are eliminated, and stearine, palmitine, or oleine 
is produced. 

By a similar process, compounds have been formed from glycerine with 
1 and 2 molecules of the fatty acids, so that we are acquainted, in the 
stearine series, for example, with — 







Stearic acid. Glycerine. 




Monostearine, 


• C 21 H 42 4 = 


^18^36^2 + C 3 H 8 3 


- H 2 


Bistearine, . 


. C 39 H 76 5 == 


2 ( C 18 H 36°2) + C 3 H 8°3 


- 2H 2 


Terstearine, . 


• C 57 H 110 O 6 = 


3(C 18 H 36 2 ) + C 3 H 8 3 


- 3H 9 



The last representing stearine as it exists in the natural fats. 

Nor is it only with the fatty acids, properly so called, that glycerine 
will furnish glycerides, as these bodies are termed, similar compounds 
having been obtained with acetic and benzoic acids. 

By heating together molecular weights of glycerine and boracic acid as 
long as steam is evolved, Barff obtained boro-glyceride C 3 H 5 B0 3 as a hard 
glacial mass soluble in water, and very efficacious for preserving milk and 
flesh. 

The hydrogen-acids are also capable of acting upon glycerine in a similar manner. 
Thus, when glycerine (C 3 H 8 3 ) is acted on by hydrochloric acid, an oily liquid, 
chlorhydrine C 3 H 5 (H0) 2 C1 is obtained. 

Dichlorhydrine C 3 H 5 (H0)C1 2 , and trichlorhydrine (C 3 H 5 C1 3 ), have also been ob- 
tained. 

By the action of silver oxide in presence of water, the chlorhydrines may be 
reconverted into glycerine. The examination of these chlorhydrines has pointed out 
the method of effecting the conversion of a triatomic alcohol (glycerine) into a diatomic 
alcohol (glycol), for if chlorhydrine be acted on by sodium dissolved in mercury, in 
the presence of water, it is converted into the glycol of propylene — 

C 3 H 5 (H0) 2 C1 + H 2 + Na 3 = C 3 H fi (HO) 2 + NaHO + NaCl . 
Chlorhydrine. Propyl-glycol. 

This tendency of glycerine to form compounds with the acids, the 
formation of which is attended (like that of the ethers from alcohol) with 
separation of the elements of water, has led chemists to look upon glyce- 
rine as an alcohol — a view which is also supported by its combining with 
sulphuric and phosphoric acids to form sulphogly eerie (C 3 H 5 (HO) 2 HS0 4 
and phosplioglycerie acids, just as alcohol forms sulphethylic and phos- 
phethylic acids. A compound has even been obtained, which is believed 
to stand to glycerine in a relation similar to that which ether bears to 
alcohol; the formula of this gly eerie ether, as it is called, is (C 3 H 5 ) 2 3 , 
differing from 2 molecules of glycerine (C 6 H 16 6 ) by the elements of 3 
molecules of water. 

Gylceric aldehyde, C 3 H 6 3 , is said to be obtained by electrolysing a 
mixture of glycerine with dilute sulphuric acid. 

Monosodium glyceride C 3 H 7 ]N"a0 3 , and disodium glyceride C 3 H 6 Na 2 3 , 
have been obtained by the action of sodium on glycerine. 

The formation of stearine from stearic acid and glycerine is quite 
analogous to that of acetic ether, for example, from acetic acid and alcohol, 
as will be seen by comparing the two equations— 

H.C 2 H 3 2 + C 2 H 5 .HO = C 2 H 5 .C 2 H 3 2 -1- H 2 

Acetic acid. Alcohol. Acetic ether. 



3(H.C 18 H 35 2 ) + C 3 H 5 .H 3 3 = C 3 H 5 .3C 1S H 35 2 + 3H 2 



Stearic acid. 



GLYCEKINE. 577 

The only difference between the two reactions is, that in the latter, 3 
molecules of acid are concerned, and 3 molecules of water are formed, 
This circumstance, taken together with some other features of glycerine, 
has induced those chemists who consider alcohol as formed upon the type 
of a molecule of water, to look upon glycerine as derived in a similar 
manner from 3 molecules of water, in which half the hydrogen is replaced 
by the triatomic radical, glyceryls (C 3 H 5 )'" ; thus — 



Type, 


H 
H 


Alcohol, 


C 2 H 5 
H 


Ether, 


C 2^5 
C 2 H 5 



Type, 



H 3 
H 3 



q Glyceric alcohol, (C 3 H 5 )'" ) q 

or glycerine, H 3 ) 3 

Glyceric ether, ffi^t, 1 °s 

410. Glycerine is obtained on the small scale by boiling olive oil with 
litharge and water, until the stearic, oleic, and palmitic acids are converted 
into their lead-salts (lead plaster), which are insoluble, whilst the glyce- 
rine, together with a little lead oxide, pass into solution. The lead is 
precipitated by hydrosulphuric acid, and the filtered liquid concentrated 
by evaporation. 

The chief uses of glycerine as an application to the skin, and a remedy 
in cases of deafness, depend upon its oily consistency, and its want of 
volatility, which preserves surfaces to which it is applied in a moist and 
supple condition. 

Glycerine boils at 290° C, but cannot be distilled alone without 
decomposition, though it has been seen to be capable of distillation 
in a current of highly heated steam. When decomposed by distilla- 
tion, it evolves very irritating vapours of acroleins (C 3 H 4 0), which 
is a constant product of the destructive distillation of fats containing 
glycerine, and gives rise to the peculiar disgusting odour of a smouldering 
tallow candle ; composite candles, being made of stearic and palmitic 
acid (without glycerine) do not emit this odour of acroleine when blown 
out. 

Acroleine is obtained in the pure state by distilling glycerine with 
phosphoric anhydride, which removes 2 molecules of water (C 3 H 8 3 
- 2H 2 = C 3 H 4 0). It may also be prepared by strongly heating 100 grms. 
of glycerine with 50 grms. of hydropotassic sulphate, in a 1500 c.c. flask, 
and distilling into a receiver placed in ice. It is a colourless liquid, 
distinguished by its intensely irritating vapour, which affects the eyes 
very strongly. From a chemical point of view it is interesting, as being 
the aldehyde of the allyle series (see p. 486), and, therefore, another link 
connecting that series with glycerine. By treatment with silver oxide, 
acroleine is converted into acrylic acid (C 3 H 4 2 ). bearing the same relation 
to acroleine (C 3 H 4 0) that acetic acid (C 2 H 4 2 ) bears to ordinary aldehyde 
(C 2 H 4 0). Allyle iodide and allylic alcohol have been already noticed 
(page 486). 

The allyle series, therefore, is perfectly parallel with the ethyle 
series, and it seems very probable that allylic alcohol is a member of 
a homologous series of alcohols having the general formula C M H 2n O, 
with a series of acids corresponding to the acetic series, but having 
the general formula C n H 2 „_ 2 2 , of which the following members are 
known : — 

2o 



578 



ACIDS OF THE ACRYLIC SERIES. 



Acrylic Series of Acids. 



Acid. 


Formula. 


Source. 


Acrylic, . 


C 3 H 4 2 


Oxidation of acroleine. 


Crotonic, 


C 4 H 6 2 


Croton-seed oil. 


Angelic, 


C 5 H 8 2 


Angelica root. 


Pyroterebic, . 


C^Hio^ 


Turpentine. 


Damaluric, 


C 7 H 12 2 


Cow's urine (8d/xa\os, a calf). 


Campholic, 


Ci H 18 O 2 


Camphor. 


Cimicic, . 


^14H 2 60 2 


Tree-bug. 


Moringic, 


C15H2802 


Moringa aptera (oil of ben). 


Hypogeic, 


[ C 16 H 30 O 2 


[ Oil of ground nut. 


Physetoleic, . 


| Sperm-whale oil (Physeter rnacrocephalus). 


Oleic, . 


^18 "34^2 


Most oils. 


Doeglic, 


Ci9H 3fi 2 


Doegling train oil. 


Brassic, 


j C 22 H 4 . 2 2 


K Mustard seed (fixed) oil. 


Eracic, . 


( Colza oil (Brassica olcifera). 



These acids are monobasic, their salts being formed by the replacement of 1 atom 
of hydrogen by a metal. Each of these acids, when fused with potassium hydrate, 
yields potassium acetate together with the potassium salt of some other member of 
the acetic series ; C 3 H 4 2 (acrylic) + 2KHO = KC 2 H 3 2 (acetate) + KCH0 2 (formiate) 
+ H 2 . In a similar way, crotonic acid yields two molecules of the acetate ; angelic 
yields acetate and propylate ; oleic yields acetate and palmitate. 

The following table exhibits the principal members of the allyle series, together 
with the corresponding members of the ethyle series : — 



Ethyle Series. 
Ethyle, 
Ether, 
Alcohol, 
Ethyle iodide, 
Acetic ether, 
Aldehyde, . 
Acetic acid, 
Ethyle sulphid 
Triethylamine, 
Tetrethylium hy- 
drate, 

It has been seen 



C 2 H 5 . C 2 H 5 

(0 2 H 5 ). 2 
C 2 H 5 .H0 
C 2 H 5 1 



C 2 H 4 2 

(C 2 H 5 ) 2 S 
N(C 2 H 5 ) 3 

N(C 2 H 5 ) 4 .HO 



Allyle, 
Allylic ether, 
Allylic alcohol, 
Allyle iodide, . 
Allyle acetate, . 
Allyle aldehyde, 
Acrylic acid, 
Allyle sulphide, 
Triallylamine, . 
Tetrallylium hy- 
drate, 



Allyle Series. 



CsHg.CgHg 

(C 3 H 5 ) 2 
CKL.HO 



C 3 H 4 (acroleine) 
C 3 H 4 2 

(C 3 H 5 ) 2 S (oil of garlic) 
N(C 3 H 5 ) 3 

N(C 3 H 5 ) 4 .HO. 



?e 486) that glycerine, when distilled with PI 2 
yields allyle iodide (C 3 H 5 I). When this liquid is treated with bromine, 1 
it yields a crystallisable allyle tribromide, C 3 H 5 Br 3 ; and if this be decom- 
posed by silver acetate, it furnishes the glyceride known as teracetine, 
thus — 

C 3 H 5 Br 3 + 3AgC 2 H 3 2 = C 3 H 5 .3C 2 H 3 2 + 3AgBr. 

Allyle tribromide. Silver acetate. Triacetine. 

When triacetine is submitted to the action of barium hydrate, glycerine 
is reproduced — 

2(C 3 H 5 .3C 2 H 3 2 ) + 3Ba(HO) 2 = 2C 8 H 5 (HO) 8 + 3Ba(C 2 H 3 2 ) 2 

Triacetine. Glycerine. Barium acetate. 

This affords an interesting example of the conversion of a monatomic 
radical, allyle (C 3 H 5 )', into a triatomic radical, glyceryle (C 3 H 5 )'". 

Glycerine may be obtained from propane by the following reactions :— (1) C 3 H 8 
(propane) +C1 4 =C 3 H 6 C1 2 (propene dichloride) +2HC1. (2) C 3 H 6 C1 2 + IC1==C 3 H 5 C1 3 
(gly cyle trichloride) + HI. (3) C 3 H 5 C1 3 + 3H 2 = C 3 H 5 (OH) 3 (glycerine) + 3HCI. 

411. A very interesting chemical similarity has been pointed out 
between glycerine and mannite (C 6 H 14 6 ). It will be remembered that 
the former is a constant product of the alcoholic fermentation, and the 



GLUCO -TARTARIC ACID — NITROGLYCERINE. 579 

latter, of a peculiar kind of fermentation (the viscous), to which saccha- 
rine liquids are subject. 

When mannite is heated, under pressure, with the acids of the acetic 
series, it forms compounds corresponding to those obtained when glycerine 
is so treated. Thus, with stearic acid — 

^6^14^6 + 6 Cl8 H 36°2 = C m H 216 O n + 7H 2 O v 
Mannite. Steaiic acid. Mannite stearine. 

But it will be observed that 7 molecules of water are here eliminated 
instead of 3, as in the case of glycerine. The further examination of 
mannite explains this, for it is not that substance which is the true ana- 
logue of glycerine, but one which is obtained by heating mannite to 400° 
I\, when it loses a molecule of water, and is converted into mannitane — 

C 6 H 14 6 - H 2 = C 6 -H 12 5 

Mannite. Mannitane. 

This mannitane or mannite-glycerine is a viscous substance, presenting 
a very strong resemblance to glycerine, so that it is not unlikely to have 
been mistaken for this substance in examining some of the natural fats. 
The mannite-glycerides, or compounds formed by heating mannite with 
tbe fatty acids, are scarcely to be distinguished from stearine, palmitine, 
&c. They are saponified by alkalies in exactly the same manner. 

Cane-sugar and grape-sugar are capable of forming compounds corre- 
sponding to those obtained by the action of acids upon glycerine and 
mannite. Thus, if grape-sugar be heated to 250° F. for several hours in 
contact with stearic acid, it is converted into a fusible solid, insoluble in 
water, but soluble in alcohol and ether — 

C 6 H 12°6 + 2C 18 H 36°2 = C 42 H 78 7 + 3H 2° • 
faXn-oS Stearic acid ' Stearic S luC0Se • 

When grape-sugar is heated with tartaric acid, a similar reaction takes 
place, but the resulting product is a new acid — 

C 6 H 12 6 + 2H 2 C 4 H 4 6 = H,C 14 H I6 15 + 3H 2 0. 

p ra P l '" suga ^ Tartaric acid. Glnco-tartaric acid, 

(anhydrous). 

; Cane-sugar behaves in a similar manner. 

412. Nitroglycerine or glonoine. — This violently explosive substance is 
very easily prepared by dissolving glycerine in a mixture of equal measures 
of the strongest nitric and sulphuric acids, previously cooled, and pouring 
the solution in a thin stream into a large volume of water, when the 
nitroglycerine is precipitated as a colourless heavy oil (sp. gr. 1 *6). It is 
advisable to add the glycerine to the mixed acids in very small quantities 
at a time, and to cool the mixture in a vessel of water after each addition. 
When the nitroglycerine has subsided, the water may be poured off, and 
the oil shaken several times with water, so as to wash it thoroughly. 

Nitroglycerine is the nitric ether of glycerine, and its formation is 
explained in the following equation — 

C3IX3O3 + 3(HN0 3 ) = C s H 5 (N"O s ) 8 + 3H 2 0. 

Glycerine. Nitroglycerine. 

On a larger scale, a mixture of concentrated nitric acid (sp. gr. 1 '47 to 1 "49) with 
twice its weight of concentrated sulphuric acid is employed. The mixture is placed 
in stone jars containing about 7 lbs. each, which are immersed in running water, and 
about 1 lb. of glycerine (sp. gr. 1'25) is gradually added, with frequent stirring, to the 
contents of each jar, care being taken that the temperature does not rise above 80° F. 



580 NITROGLYCERINE. 

The mixture is allowed to settle for a quarter of an hour, and poured gradually into 
5 or 6 gallons of water. The oily nitroglycerine which falls to the bottom is well 
washed by stirring with water, a little alkali being added in the last washings. One 
per cent, of magnesia is sometimes added to the nitroglycerine in order to neutralise 
any acid arising from decomposition. 

This oil is very violent in its explosive effects. If a drop of nitro- 
glycerine be placed on an anvil and struck sharply, it explodes with a 
very loud report, even though not free from water; and if a piece of 
paper moistened with a drop of it be struck, it is blown into small frag- 
ments. On the application of a flame or of a red hot iron to nitro- 
glycerine, it burns quietly; and when heated over a lamp in the open air 
it explodes but feebly. In a closed vessel, however, it explodes at about 
360° F. with great violence. For blasting rocks, the nitroglycerine is 
poured into a hole in the rock, tamped by filling the hole with water, 
and exploded by the concussion caused by a detonating fuze (see page 512). 
It has been stated to produce the same effect in blasting as ten times its 
weight of gunpowder, and much damage has occurred from the accidental 
explosion of nitroglycerine in course of transport. When nitroglycerine 
is kept, especially if it be not thoroughly washed, it decomposes, with 
evolution of nitrous fumes and formation of crystals of oxalic acid; and 
it may be readily imagined that, should the accumulation of gaseous pro- 
ducts of decomposition burst one of the bottles in a case of nitroglycerine, 
the concussion would explode the whole quantity. 

Nitroglycerine, like gun-cotton, is particularly well fitted for blasting, 
because it will explode with equal violence whether moisture be present 
or not, but it has the advantage of containing enough oxygen to convert 
all its carbon into carbonic acid gas. On the other hand, it is very 
poisonous, and is said to affect the system seriously by absorption through 
the skin, and the gases resulting from its explosion are exceedingly acrid. 
Again, its fluidity prevents its use in any but downward bore-holes. To 
overcome these objections, and to diminish the danger of transport, several 
blasting compounds have been proposed, of which nitroglycerine is the 
basis. 

Dynamite is composed of a particularly porous siliceous earth (Kiesel- 
fjuhr), obtained from Oberlohe in Hanover, impregnated with about 
70 or 75 per cent, of nitroglycerine. 

Kieselguhr contains 63 per cent, of soluble silica, about 18 of organic 
matter, 11 of sand and clay, and 8 of water. It is incinerated to expel 
the organic matter, and mixed with the nitroglycerine in wooden troughs 
lined with lead. 

When used in solid rock, dynamite is 6 or 7 times as strong as blasting- 
powder. 

NobeVs detonators for nitroglycerine contain 7. parts of mercuric ful- 
minate and 3 parts of potassium chlorate, pressed into small copper tubes. 

Fatal accidents have occurred in using dynamite, in consequence 
of exudation of nitroglycerine from the dynamite, caused by contact with 
water in the bore-holes; this nitroglycerine having been afterwards 
exploded by the drill in boring fresh holes. 

Glyoxyline is a name given to gun-cotton pulp and saltpetre mixed with 
nitroglycerine. Lithofracteur is a more complex mixture containing 
about half its weight of nitroglycerine, together with nitrate of soda 
sulphur, powdered coal, sawdust, and siliceous earth. Dualine is com 



OILS AND FATS. 581 

posed of nitroglycerine and sawdust. Nitromagnite contains nitroglycerine 
and magnesia. 

Blading gelatine is made by dissolving collodion-cotton (p. 513) in 
about nine times its weight of nitroglycerine; it's detonation is even more 
powerful than that of nitroglycerine itself. The readiness with which it 
may be exploded by a detonating fuze charged with mercuric fulminate is 
greatly increased by incorporating it with about one-tenth of its weight 
of gun-cotton. On the other hand, its liability to accidental detonation 
may be reduced by intimately mixing it with a small proportion of 
camphor, the action of which does not appear to be understood. 

Nitroglycerine is readily soluble in ether and in wood-naphtha, but 
somewhat less so in alcohol; it is reprecipitated by water from these last 
solutions. It becomes solid at 40° F., a circumstance which is unfavour- 
able to its use in mining operations, partly because it is then less sus- 
ceptible of explosion by the detonating fuze, and partly because serious 
accidents have resulted from attempts to thaw the frozen nitroglycerine 
by heat, or to break it up with tools. It is remarkable that when made 
on the small scale, the nitroglycerine may generally be cooled down 
to 0° F. without becoming hard. This and other observations render 
it probable that some other substitution product is occasionally mixed 
with it. 

Nitroglycerine C 3 H 5 (]Sr0 3 )3 stands in the same relation to the triatomic alcohol 
glycerine C 3 H g (HO) 3 , in which nitric ether C 2 H 5 (N0 3 ) stands to ordinary monatomic 
alcohol C 2 H 5 (HO). Berthelot finds that, in the formation of nitric ether by the action 
of nitric acid upon alcohol, 5800 heat units are disengaged for each molecule of nitric 
acid entering into the reaction, whereas, in the formation of nitroglycerine, only 4300 
heat units, per molecule of nitric acid, are disengaged. Less energy having been 
converted into heat in the latter case, more is stored up in the nitroglycerine, and 
hence its formidable effect as an explosive. In the formation of gun-cotton, each 
molecule of nitric acid disengaged 11,000 heat units, to which Berthelot attributes 
the stability and inferior explosive effect of gun-cotton in comparison with nitro- 
glycerine. 

Oils and Fats. 

413. A very remarkable feature in the history of the fats is the close 
resemblance in chemical composition and properties which exists between 
them, whether derived from the vegetable or the animal kingdom. They 
all contain two or more neutral substances which furnish glycerine when 
saponified, together with some of the acids of the acetic series or of series 
closely allied to it. 

One of the most useful vegetable fatty matters is palm oil, which is 
extracted by boiling water from the crushed fruit of the Elais guineensis, 
an African palm. It is a semi-solid fat, which becomes more solid when 
kept, since it then undergoes a species of fermentation, excited apparently 
by an albuminous substance contained in it, in consequence of which the 
palmitine (C 51 H 98 6 ) is converted into glycerine and palmitic acid. The 
bleaching of palm oil is effected by the action of a mixture of sulphuric 
or hydrochloric acid and potassium dichromate, which oxidises the yellow 
colouring matter. 

Cocoa-nut oil is also semi-solid, and is remarkable for the number of 
acids of the acetic series which it yields when saponified, viz., caproic, 
caprylic, rutic, lauric, myristic, and .palmitic. 

These fats are chiefly used in the manufacture of soap and candles. 

Salad oil or sweet oil (olive oil) is obtained by crushing olives, and an 



582 



OXALIC ACID SERIES. 



inferior kind which is used for soap is obtained by boiling the crushed 
fruit with water. When exposed to a temperature of about 32° F. a con- 
siderable portion of the oil solidifies ; this solid portion is generally called 
margarine (C 54 H 104 O 6 ) ; it is much less soluble in alcohol than stearine, 
though more so than palmitine. When saponified, margarine yields 
glycerine and margaric acid (C 1 ^H 34 2 ). This acid appears to be really 
composed of stearic and palmitic acids, into which it may be separated by 
repeated crystallisation from alcohol, when the palmitic acid is left in 
solution. The fusing-point of margaric acid is 140° F., that of stearic 
being 159°, and that of palmitic, 144°, but a mixture of 10 parts of pal- 
mitic with 1 part of stearic acid fuses at 140°. 

That portion of the olive oil which remains liquid below 32° con- 
sists of oleine (C 5lr H 104 O 6 ), and forms nearly three-fourths of its weight. 
Oleine is not so easily saponified as the solid fats, and is resolved by 
that process into glycerine and oleic acid (C 18 H 34 2 ), which differs from the 
other fatty acids by remaining liquid at temperatures above 40° F., and 
by absorbing oxygen from the air, when it is converted into a new acid 
which is not solidified by cold. 

Oleic acid is used in greasing wool for spinning, being much more 
easily removed by alkalies than olive oil, which was formerly employed. 
Oleate of ammonia is sometimes employed as a mordant for the aniline 
dyes on cotton. 

The characteristic feature of oleic acid is its furnishing a solid crys- 
tallised acid when submitted to destructive distillation ; this acid is called 
sebacic acid, and is one of a series of dibasic acids, most of the other mem- 
bers of which may be obtained from oleic acid by the action of nitric 
acid. 

Oxalic Acid Series or Dibasic Fatty Acid Series. 



Acid. 


Formula. 


Source. 


Oxalic, 

Malonic, 

Succinic, 

Lipic, . 

Adipic, 

Pitnelic, 

Suberic, 

Anchoic,* 

Lepargylic,t 

Sebacic, 




C 2 H 2 4 ■ 
C 3 H 4 4 
C 4 H 6 4 
C 5 H 8 4 

C 6HlO°4 

C 7 H 12 4 

C 8 H 14°4 

j C 9 H 16 4 

Cl Ul8^4 


Oxalis acetosella (wood sorrel), &c. 

Oxidation of malic acid. 

Amber (succinum). 

Oxidation of oleic acid (xtiros, fat). 

,, ,, (adejjs, fat). 

,, ,, {ir?fiehr), fat). 
Oxidation of stearic acid, and of cork (suber). 

Oxidation of Chinese wax, and of cocoa-nut oil. 

Distillation of oleic acid. 



The normal salts of the acids of this series are formed by the displace- 
ment of 2 atoms of hydrogen by a metal. Thus, potassium succinate 
has the composition C 4 (H 4 K 2 )0 4 . 

It is worthy of remark, that nine acids of the series, C„H 2n 2 (from 
acetic to capric inclusive), are found among the products of the action of 
nitric acid upon oleic acid. 

It is well known that salad oil becomes rancid, and exhales a disagree- 
able odour after being kept for some time. This appears to be due to a 
fermentation similar to that noticed in the case of palm oil, originally 
started by the action of atmospheric oxygen upon albuminous matters 

* From ayx 60 ) t° throttle, from its suffocating vapours, 
f From XeVa/oyos, having white skin. 



FIXED OILS. 583 

present in the oil; the neutral fatty matters are thus partly decomposed, 
as in saponification; their corresponding acids being liberated, and giving 
rise (in the case of the higher members of the acetic series, such as caproic 
and valerianic) to the disagreeable odour of rancid oil. By boiling the 
altered oil with water, and afterwards washing it with a weak solution of 
soda, it may be rendered sweet again. 

Almond oil, extracted by a process similar to that employed for olive oil, 
is also very similar in composition; but colza oil, obtained from the seeds 
of the Brassica oleifera, contains only half its weight of oleine 7 and' hence 
solidifies more readily than the others. 

Colza oil is largely used for burning in lamps, and undergoes a process 
of purification from the mucilaginous substances which are extracted with 
it from the seed, and leave a bulky carbonaceous residue when subjected 
to destructive distillation in the wick of the" lamp. To remove these, the 
oil is agitated with about 2 per cent, of oil of vitriol, which carbonises 
the mucilaginous substances, but leaves the oil untouched. When the 
carbonaceous flocks have subsided, the oil is drawn off, washed to remove 
the acid, and filtered through charcoal. 

Linseed oil, obtained from the seeds of the flax plant, is much richer in 
oleine than any of the foregoing, exhibiting no solidification till cooled 
to 15° or 20° F. below the freezing-point. It exhibits, however, in a far 
higher degree, a tendency to become solid when exposed to the air, which 
has acquired for it the name of a drying oil, and renders it of the greatest 
use to painters. This solidification is attended with absorption of oxygen, 
which takes place so rapidly in the case of linseed oil, that spontaneous 
combustion has been known to take place in masses of rag or tow which 
have been smeared with it.* 

The tendency of linseed oil to solidify by exposure is much increased by 
heating it with about -^-th of litharge, or y^th of black oxide of manganese ; 
these oxides are technically known as dryers, and oil so treated is called 
boiled linseed oil. The action of these metallic oxides is not well under- 
stood. 

The strong drying tendency of linseed oil is supposed to be due to a 
peculiarity in the oleine, which is said not to be ordinary oleine, but to 
furnish a different acid, linoleic acid, when saponified. When linseed oil is 
exposed for some time to a high temperature, it becomes viscous and treacly, 
and is used in this state for the preparation of printing ink. If the viscous 
oil be boiled with dilute nitric acid, it is converted into artificial caout- 
chouc, which is used in the manufacture of surgical instruments. This 
property appears to be connected with the drying qualities of the oil. 

Castor oil, obtained from the seeds of Ricinus communis, also yields a 
peculiar acid when saponified, termed ricinoleic (H.C 18 H 33 3 ), containing 
one more atom of oxygen than oleic acid, which it much resembles. The 
destructive distillation of castor oil yields oenanthic acid (H.C^HjgOg) and 
oenanthole or oenanthic aldehyde (C 7 H 14 0), and by distilling it with caustic 
potash, caprylic alcohol (C 8 H 18 0) is obtained. As in the case of olive oil, 
the cold drawn castor oil, which is expressed from the seeds without the 
aid of heat, is much less liable to become rancid. Castor oil is much 
more soluble in alcohol than any other of the fixed oils. 

* During the oxidation, a volatile compound is formed which resembles acroleine in 
smell, and colours unsized paper brown. It has been suggested that the brown colour 
and musty smell of old books may be due to the oxidation of the oil in the printing-ink. 



584 SPERMACETI. 

The various fish oils, such as seal and whale oil, also consist chiefly of 
oleine, and appear to owe their disagreeable odour to the presence of cer- 
tain volatile acids, such as valerianic. 

Cod-liver oil appears to contain, in addition to oleine and stearine, a 
small quantity of acetine (C 9 H 14 6 ), which yields acetic acid and glycerine 
when saponified. Some of the constituents of bile have also been traced 
in it, as well as minute quantities of iodine and bromine. 

Butter contains about two-thirds of its weight of solid fat, which consists 
in great part of margarine (see page 573), but contains also butine, which 
yields glycerine and butic acid (H.C 20 H 39 O 2 ) when saponified. The liquid 
portion consists chiefly of oleine. Butter also contains small quantities 
of butyrine, caproine, and caprine, which yield, when saponified, glycerine 
and butyric (H.C 4 H 7 2 ), caproic (H.C 6 H n 2 ), and capric (H.C 10 H 19 O 2 ) 
acids, distinguished for their disagreeable odour. 

Fresh butter has very little odour, being free from these volatile acids, 
but if kept for some time, especially if the caseine of the milk has been 
imperfectly separated in its preparation, spontaneous resolution of these 
fats into glycerine and the volatile disagreeable acids takes place. By 
salting the butter this change is in great measure prevented. 

The fat of the sheep and ox (suet, or when melted, tallow) consists 
chiefly of stearine, whilst in that of the pig (lard) oleine predominates to 
about the same extent as in butter. Margarine (or palmitine'?) is also 
present in these fats. Benzoated lard contains some gum benzoin, which 
prevents it from becoming rancid. 

Human fat contains chiefly oleine and margarine (or, if we do not 
admit the independent existence of the latter, palmitine and stearine). 

Sperm oil, which is expressed from the spermaceti found in the brain 
of the sperm whale, owes its peculiar odour to the presence of a fat which 
has been called phocenine, but which appears to be valerine, as it yields 
glycerine and valerianic acid (H.C 5 H 9 2 ) when saponified. 

The beautiful solid crystalline fat, known as spermaceti or ceiine, differs 
widely from the ordinary fatty matters, for when saponified (which is not 
easily effected), it yields no glycerine, but in its stead another alcohol 
termed ethal (C 16 H 34 0), which is a white crystalline solid, capable of being 
distilled without decomposition. 

The soap prepared from spermaceti, when decomposed by an acid, 
yields palmitic acid (H.C 16 H 31 2 ) (formerly called ethalic acid), to which 
ethal is the corresponding alcohol. 

Palmitic acid and ethal are formed from spermaceti by the assimilation of the 
elements of water, just as stearic acid and glycerine are formed from stearine — 

C 32 H 64 2 (Spermaceti) + H 2 = C 16 H 34 (Ethal) + H.C I6 H 31 2 (Palmitic acid). 

Upon the compound radical theory, ethal would he represented as cetylic hydrate 
(C 16 H 33 )HO, and as the alcohol of the cetyle series running paralled with the ethyle 
series. The following characteristic members of the series have been studied : — 



Cetyle Series. 
Cetylene, . Ci 6 H 32 
Cetylic ether, (C 16 fi 33 ) 
Ethal, . . C 16 H 33 .HO 
Palmitic acid, C 16 H 31 2 .H 
Spermaceti, C 16 H 33 .C 16 H 31 2 



Ethyle Series. 
Ethylene, . C 2 H 4 
Ether, . (C 2 H 5 ) 2 
Alcohol, . C 2 H 5 .HO 
Acetic acid, C 2 H 3 2 .H 
Acetic ether, C 2 H 5 .C 2 H 3 2 



Chinese wax, the produce of an insect of the cochineal tribe, is 
analogous in its chemical constitution to spermaceti. When saponified 



WAX — VEGETABLE ACIDS. 



585 



by fusion with caustic potash, it yields cerotine or cerylic alcohol 
C 2r H 55 .HO), corresponding to ethal, and cerotic acid (H.C 27 H 53 2 ), 
corresponding to palmitic acid. Cerotic acid is also contained in ordinary 
bees' wax, from which it may be extracted by boiling alcohol, and 
crystallises as the solution cools. It forms about two -thirds of the weight 
of the wax. Cerotic acid is found among the products of oxidation of 
paraffin by chromic acid. 

Bees 1 wax also contains about one-third of its weight of myricine 
(C 46 H 92 2 ), a substance analogous to spermaceti, which yields, when 
saponified, palmitic acid and melissine (C 30 H 61 .HO), an alcohol corre- 
sponding to ethal. The colour, odour, and tenacity of bees' wax appear 
to be due to the presence of a greasy substance called cer oleine, which 
forms about -^th of the wax, and has not been fully examined. The tree 
tvax of Japan is said to be pure palmitine. 

Wax is bleached for the manufacture of candles, by exposing it in thin 
strips or ribands to the oxidising action of the atmosphere, or by boiling 
it with nitrate of soda and sulphuric acid. Chlorine also bleaches it, but 
displaces a portion of the hydrogen in the wax, taking its place and causing 
the evolution of hydrochloric acid vapours when the wax is burnt. 

The following table includes the principal fatty bodies and their corresponding 
acids, with their fusing points — 



Neutral 
Fats. 


Formula. 


Chief 
Source. 


Fusing 
Point, 
Fahr. 


Fatty 
Acids. 


Formula, 


Fusing 
Point, 
Fahr. 


Stearine* 

Palmitine 

Margarine 

Oleine 

Cetine 

Myricine 


^57H 110 O 6 
C51H9SO6 

^57^104^6 
^32^64^2 


Tallow 
Palm oil 
Olive oil 

Spermaceti 
Bees' wax 


125° to 157° 
114° to 145° 

116° 
Below 32° 

120° 

162° 


Stearic 
Palmitic 
Margaric 
'Oleic 
Palmitic 


^18^36^2 
Oi6H 32 2 
C 17 H 34 2 

C 18 H 34°2 

c 16 h 3 a 


159° 
144° 
140° 
40° 
144° 



VEGETABLE ACIDS. 

414. Oxalic acid. — This poisonous acid occurs pretty abundantly in 
the vegetable kingdom, being found in the leaves of the wood sorrel as 
binoxalate of potash or hydropotassic oxalate [salt of sorrel, KHC 2 4 . Aq.), 
in the stalks of rhubarb, in some sea-weeds, as sodium oxalate, and in 
lichens, some of which contain more than half their weight of oxalate of 
lime (calcium oxalate). Oxalate of lime has also been found in wood. 
Free oxalic acid is present in many fungi. In certain unhealthy conditions 
of the animal frame, calcium oxalate is produced, being either excreted 
in the urine, or forming a calculus {mulberry calculus) in the bladder. 
In such cases the oxalic acid appears to be formed in consequence of an 
imperfection in that oxidising process by which the carbon and hydrogen 
of the various parts of the frame are finally converted into carbon dioxide 
(C0 2 ) and water (H 2 0), the production of oxalic acid (C 2 H 2 4 ) representing 
the penultimate stage of that process. 

Guano contains a considerable quantity of oxalic acid in combination 
with ammonia and lime. 



* Stearine and palmitine are said to present three modifications with different fusing- 
points. Some recent observations appear to indicate that the so-called palmitine of palm 
oil really contains stearine, oleine, and laurine. 



586 PREPARATION OF OXALIC ACID. 

With the exception of carbon dioxide, no carbon compound is more 
commonly met with than oxalic acid, as a product of the action of 
oxidising agents upon organic substances, especially upon those which do 
not contain nitrogen, such as sugar (C 12 H 22 O n ), starch (C 6 H 10 O 5 ), and 
woody fibre. 

Oxalic acid is largely employed in calico-printing, in cleansing leather 
and brass, as a solvent for Prussian blue in the preparation of blue ink, 
&c, and for taking iron-mould out of linen. It is manufactured on the 
large scale by oxidising sawdust with a mixture of caustic potash and 
caustic soda; the latter would not produce oxalic acid without the 
potash, and this alone would be too expensive. One molecule of caustic 
potash and 2 molecules of caustic soda are mixed in solution, which 
should have the sp. gr. 1 '35, made into a thick paste with sawdust, and 
heated upon iron plates for several hours; hydrogen is evolved, from the 
decomposition of the alkalies, the oxygen serving to convert the wood 
into oxalic acid, which forms more than one-fourth of the weight of the 
grey mass finally obtained. On treating this mass with cold water, a 
quantity of sodium oxalate is left undissolved; this is boiled with lime, 
when the oxalic acid is converted into the insoluble oxalate of lime, and 
soda is dissolved; the oxalate of lime is then decomposed by dilute 
sulphuric acid, when the sparingly soluble sulphate of lime is formed, 
and the solution yields crystals of oxalic acid (H 2 C 2 4 .2Aq.) on evapora- 
tion. The whole of the alkali originally employed is recovered by 
evaporating the liquors to dryness, calcining to destroy organic matter, 
and decomposing the alkaline carbonates with lime. The sawdust yields 
about half its weight of crystallised oxalic acid. 

Before the introduction of this process, oxalic acid was sold at nearly 
twice its present cost, being then usually obtained by the action of nitric 
acid either upon molasses or upon starch-sugar* (page 501) in leaden 
vessels, which were found to remain unattacked by the acid as long as any 
sugar remained unoxidised. 

For experiment on the small scale, oxalic acid may be prepared by gently heating 
100 grains of starch with 1£ measured ounce of nitric acid, sp. gr. 1 '38, when abundant 
fumes of N 2 3 will indicate the deoxidation suffered by the nitric acid. When this' 
has abated, the solution may be transferred to a dish, and slowly evaporated to 
about one-sixth of its bulk ; on cooling, a mass of beautiful four-sided prismatic 
crystals of oxalic acid will be obtained. 

The crystals of oxalic acid may be represented by the empirical formula 
C 2 H 6 6 , but when they are heated to 212° F. they lose water, melting 
first, if the heat be suddenly applied, but efflorescing without fusion if 
heated gradually. By suddenly heating the crystals in a test-tube, much 
of the acid may be sublimed in long prismatic crystals. The dried or 
effloresced oxalic acid has the composition C 2 H 2 4 , showing that 2 
molecules of water of crystallisation have been expelled, and that the 
crystals would be more correctly represented by C 2 H 2 4 .2Aq.f On 
neutralising oxalic acid with potash and soda, salts are obtained which, 
when dried at 212° F., have the composition K 2 C 2 4 and Na 2 C 2 4 , and 
if solutions of these salts be precipitated by nitrate of lead or of silver, 
the oxalates of lead (PbC 2 4 ) and of silver (Ag 2 C 2 4 ) are obtained. If 

* Hence the common name, acid of sugar. 

+ Villiers has obtained large rhombic octahedra of H 2 C 2 4 by dissolving crystallised 
oxalic acid in 12 parts of warm oil of vitriol and setting aside. 



PROPERTIES OF OXALIC ACID. 587 

the dried acid be heated to about 320° E., it sublimes in crystals, but 
above that temperature it is decomposed into water, carbon dioxide, 
carbonic oxide, and some formic acid (see page 568). When heated with 
dehydrating agents, such as sulphuric acid, it is also decomposed into 
carbon dioxide and carbonic oxide (page 90). 

Oxalic acid is rather sparingly soluble in cold water, requiring about 
nine times its weight; hot water dissolves it more abundantly, and it is 
moderately soluble in alcohol. The aqueous solution is intensely acid, 
more nearly resembling the strong mineral acids than one of vegetable 
origin, and is exceedingly poisonous, a property which is the more 
dangerous on account of the resemblance of the crystallised oxalic acid to 
Epsom salts (sulphate of magnesia), from which, however, it may be 
readily distinguished by its sour taste and by the action of heat, which 
entirely dissipates the oxalic acid, but only expels water from Epsom 
salts. Fortunately, a considerable quantity of the acid is required to 
cause death; in ordinary cases, 100 grains or more. The chemical 
antidote employed to counteract its effect is chalk suspended in water, 
the lime of the chalk combining with the acid to form the insoluble and 
harmless calcium oxalate (CaC 2 4 ). The insolubility of this oxalate 
readers the oxalic acid one of .the most delicate tests for lime, which may 
be detected, for example, in common water, by adding oxalic acid and a 
slight excess of ammonia, when a white cloud of oxalate of lime is pro- 
duced. Conversely, of course, salts containing calcium (calcium chloride, 
for instance) may be employed to detect oxalic acid, the precipitated 
calcium oxalate being distinguished from other similar precipitates by its 
insolubility in acetic acid. 

As might be expected from its composition (C 2 H 2 4 ), oxalic acid is 
easily converted into carbon dioxide and water by oxidising agents ; thus, 
if a hot solution of oxalic acid be poured upon powdered manganese 
dioxide, violent effervescence takes place from the rapid evolution of 
carbonic acid gas. 

Hydropotassic oxalate, or binoxalate of potash (KHC 2 4 .H 2 0), is sold 
under the names of salt of sorrel and essential salt of lemons, and is employed 
for the same purposes as oxalic acid. It is a sparingly soluble salt, 
requiring 40 parts of cold water to dissolve it, and has occasionally caused 
accidents by being mistaken for cream of tartar (hydropotassic tartrate), 
from which it is readily distinguished by the action of heat, which chars 
tartrate, but not the oxalate, an alkaline mass containing potassium 
carbonate being left in both cases. 

Trihydrojootassic oxalate, or quadroxalate of potash (KH 3 2C 2 4 .2H 2 0), 
is also sometimes sold as salts of lemon; it is even less soluble than the 
binoxalate. 

Ammonium oxalate (NH 4 ) 2 C 2 4 .H 2 0, so much used in chemical 
analysis as a precipitant for lime, is obtained by mixing solution of 
oxalic acid with a slight excess of ammonia, and evaporating the solution, 
from which the oxalate crystallises, on cooling, in fine prismatic needles. 

The action of heat upon this salt has been described at page 550. 

Silver oxalate (Ag 2 C 2 4 ) is obtained as a white precipitate when nitrate 
of silver is added to ammonium oxalate. It is remarkable for being de- 
composed, with a slight explosion, when heated in the dry state, metallic 
silver being left, Ag 2 C 2 4 = Ag 2 + 2C0 2 . 

Potassium-ferrous oxalate, prepared by adding potassium oxalate in 



588 PREPARATION OF TARTARIC ACID. 

excess to ferrous sulphate, is a very powerful reducing agent, useful in 
photography. 

415. Tartaric acid.' — The most important of the vegetable acids is 
tartaric acid (C 4 H 6 6 ), which occurs in many fruits, but more especially in 
the grape, the juice of which deposits it, during fermentation, in the form 
of hydropotassic tartrate or bitartrate of potash, which is known in 
commerce as tartar or argol. This salt dissolves with difficulty in cold 
water, but may be dissolved in boiling water, from which it crystallises in 
prisms on cooling. When thus purified, it is known as cream of tartar, 
and has the composition KHC 4 H 4 6 , representing tartaric acid in which 
1 atom of hydrogen has been replaced by potassium. The solution of this 
salt is acid to test-papers, and if it be neutralised with potash and evapo- 
rated, it yields crystals of a very soluble salt, having the composition 
K 2 C 4 H 4 6 . This is the normal potassium tartrate, cream of tartar being 
the acid tartrate. The crystallised tartaric acid is therefore regarded as 
H 2 C 4 H 4 6 . 

In order to prepare tartaric acid, which is largely used in dyeing and 
calico-printing, the impure bitartrate of potash is boiled with water, and 
calcium carbonate (chalk) is added as long as it causes effervescence from 
the escape of carbonic acid gas; the result of this change is the formation 
of calcium tartrate, which is insoluble, and potassium tartrate, which 
dissolves in water — 

2(KHC 4 H 4 6 ) + 2CaC0 3 = K 2 C 4 H 4 6 + CaC 4 H 4 6 4- H 2 + 2C0 2 . 

Calcium chloride is then added to the mixture, which converts the whole 
of the tartaric acid into the insoluble calcium tartrate — 

K 2 C 4 H 4 6 + CaCl 2 = 2KC1 + CaC 4 H 4 G . 

The calcium tartrate is strained off, washed, and boiled with diluted sul- 
phuric acid, when calcium sulphate remains undissolved, and tartaric acid 
may be obtained in crystals by evaporating the filtered solution — • 

CaC 4 H 4 6 + H 2 S0 4 = H 2 C 4 H 4 6 + CaS0 4 . 

Large transparent prisms are thus obtained, which are soluble in about three-, 
fourths of their weight of hot water. When kept, the solution, unless 
very strong, deposits a curious fungoid growth,* and acetic acid is found 
in it. When heated to about 340° F., the crystals fuse without loss of 
weight ; but on examining the fused mass, it is found to be no longer 
tartaric acid, but a mixture of two new acids. One of these, metatartaric 
acid, has the same formula as tartaric acid (H 2 C 4 H 4 6 ), but cannot be 
crystallised. Its salts are more soluble in water than the tartrates, and 
are converted into the latter when boiled with water. The other acid, 
isotartaric, is also uncrystallisable, but has the formula (HC 4 H 5 6 ). The 
potassium isotartrate (KC 4 H 5 6 ) has the same composition as the bitar- 
trate (KHC 4 H 4 6 ), but is far more soluble. It is converted into that 
salt by boiling with water. 

At 374° F. tartaric acid loses water, and is converted into tartaric 
anhydride (C 8 H 8 O 10 ), which is a white insoluble substance, convertible 
into tartaric acid by prolonged contact with water. 

Tartar-emetic. — One of the commonest salts of tartaric acid is tartar- 
emetic, the double tartrate of antimony and potassium, which is prepared 

* This fungus lias been found to contain 3*5 per cent, of nitrogen. 



TART AE- EMETIC. 589 

"by boiling antimony with sulphuric acid, driving off the excess of acid by 
heat, and digesting the residual antimonious oxide with cream of tartar 
and a little water for some hours. The changes involved in the process 
are thus represented — 



Sb 2 


+ 3H 2 S0 4 = 


Sb 2 3 


+ 3H 2 + 


3S0 2 


3 + 


2KHC 4 H 4 O 

Bitartrate of potash. 


= 2(K 


SbO.C 4 H 4 ( 

fai tar-emetic. 


.) + H 2 0. 



Sb 2 

On boiling the mixture with water, and filtering, the cooled solution 
deposits octahedral crystals, of the formula 2(K.SbO.C 4 H 4 6 ).Aq.^ 

The water of crystallisation may be expelled at 212° F. ; and if the salt 
be heated to 400° F. it loses an additional molecule of water, and becomes 
K.Sb.C 4 H 2 6 , which is reconverted into tartar-emetic when dissolved in 
water. 

When a little hydrochloric acid is added to a solution of tartar-emetic, a precipi- 
tate of antimonious oxide is formed, which dissolves easily in an excess of the acid. 
If kept for a length of time in solution, tartar-emetic is decomposed, octahedral 
crystals of antimonious oxide being deposited, and the solution ceases to be preci- 
pitated by hydrochloric acid. The reaction to test-paper, which was slightly acid, 
is now slightly alkaline. 

Compounds perfectly analogous to tartar-emetic have been obtained, in which the 
antimony is replaced by boron or by arsenic, and the potassium by silver, lead, or 
sodium. 

It will be observed that tartar-emetic presents an anomaly in its composition, for 
it might be expected to be KSb"'(C 4 H 4 6 ) 2 . The composition of the tartar-emetic, 
dried at 400° F. , might he reconciled with that of crystallised tartaric acid by repre- 
senting it thus, C 4 (H 2 KSb"')0 6 , that is, crystallised tartaric acid (C 4 H 6 6 ), in which 
1 atom of hydrogen has been replaced by potassium, and 3 atoms by the triatomic 
antimon}'. The relation existing between tartaric acid, its potassium salts, and the 
emetics, will be seen in the following formulae- - 

Tartaric acid, .... H 2 C 4 H 4 6 

Potassium tartrate, . . . K 2 C 4 H 4 6 

Cream of tartar, . . . KHC 4 H 4 6 

Tartar-emetic, . . . KHC 4 HSb0 6 . 

The beautiful prismatic crystals known as Roclielle salt consist of a 
double tartrate of potassium and sodium (KNaC 4 H 4 G .4Aq.), prepared by 
neutralising cream of tartar with sodium carbonate. 

Tartaric acid has been obtained artificially by the action of nitric acid 
on sugar of milk and on gum, which supplies a link of connexion between 
this acid and the members of the sugar group which accompany it in 
plants. 

Tartaric acid is easily convertible into succinic and malic acids, as might 
be anticipated from an inspection of their formulae — 

Tartaric acid, H 2 C 4 H 4 6 ; malic acid, H 2 C 4 H 4 5 ; succinic acid, 
H 2 C 4 H 4 4 . 

When tartaric acid is heated with phosphorus and iodine in the presence 
of w T ater (or, which amounts to the same thing, when it is heated with 
hydriodic acid), the acid is deoxidised, and malic and succinic acids are 
produced, thus, H 2 C 4 H 4 6 + 4HI = H 2 C 4 H 4 4 + I 4 + 2H 2 0. 

Tartaric acid. Succinic acid. 

Tartaric and malic acids are frequently associated in fruits, and succinic 
acid is found among the products of fermentation of grape-juice. 

Succinic acid may be reconverted into tartaric acid by heating it with 
bromine and water, when it is . converted into bibromosuccinic acid, 



590 . EACEMIC ACID. 

H 2 C 4 (H 2 Br 9 )0 4 , which furnishes tartaric acid when decomposed with 
silver oxide ; H 2 C 4 (H 2 Br 2 )0 4 + Ag 2 + H 2 = H 2 C 4 H 4 6 + 2AgBr. 

When bromosuccinic acid, H 2 C 4 (H 3 Br)0 4 , is decomposed with silver 
oxide, malic acid is formed — 

2H 2 C 4 (H 3 Br)0 4 + 3Ag 2 = 2Ag 2 C 4 H 4 5 + 2AgBr + H 2 . 

Bromosuccinic acid. Silver malate. 

The synthesis of succinic acid has been effected by the following series of re- 
actions : — 

C 2 + H 2 = C 2 H 2 (acetylene); C 2 H 2 + H 2 - C 2 H 4 (ethene); C 2 H 4 + Br 2 = C 2 H 4 Br 2 
(ethene dibromide); C 2 H 4 Br 2 + 2KCN = 2KBr + C 2 H 4 (CN 2 ) (ethene dicyanide) ; 
C 2 H 4 (CN) 2 + 2KHO + 2H 2 = 2NH 3 + K 2 C 4 H 4 4 (potassium succinate). 

416. -The tartaric acid found in grapes is accompanied, particularly in those of 
certain vintages and districts, by another acid called racemic or paratartaric acid, 
which has the same composition as tartaric acid, but crystallises with a molecule 
of water (H 2 C 4 H 4 6 .Aq.). The crystalline forms of these acids are the same, but 
the crystals of racemic acid effloresce, from loss of water when exposed to the air. 
Solution of racemic acid is precipitated by the salts of calcium, which do not precipitate 
tartaric acid unless it be previously neutralised. Moreover, although racemic acid 
forms, with potash and antimonious oxide, a salt corresponding in composition to 
tartar-emetic, this does not crystallise in octahedra, but in tufts of needles. 

There is a marked difference in the action of these two acids and their salts upon 
polarised light, for solutions of racemic acid and the racemates do not alter the plane 
of polarisation, whilst tartaric acid and the tartrates rotate it to the right. 

On carefully examining the crystalline forms of the tartrates, Pasteur observed 
that they generally presented an exception to that law of crystalline symmetry, which 
requires that a modification existing on an edge or face of a crystal should be 
repeated on all its other similar edges or faces, whereas in the crystals of the tartrates, 
certain of the edges are truncated without any corresponding modification of the 
others, and heniihedral forms are thus produced. Now, in general, it is found that 
if a substance forms hemihedral crystals, their hemihedrism is of such a character 
that they can be superposed upon each other, so that the united crystals shall exhibit 
a perfect symmetry upon each side of the plane of junction ; but the hemihedrism of 
the tartrates is such, that the crystals do not exhibit this symmetry when superposed 
upon each other, but when one is superposed upon the reflection of the other in a 
mirror, so that instead of presenting crystals which are, as usual, partly right and 
partly left-handed in their want of symmetry, the crystals of the tartrates are either 
all right-handed or all left-handed hemihedral crystals. 

"When the action of solutions of these salts upon polarised light came to be 
examined, it was found that the right-handed crystals always rotated the plane of 
polarisation to the right, whilst the left-handed crystals produced a left-handed 
rotation. 

On separating the acids from these salts, they resembled each other precisely in 
all their chemical properties, but the acid from the right-handed salts furnished 
crystals which were hemihedral right-handedly, whilst that of the left-handed salts 
furnished left-handed hemihedral crystals ; moreover, the solution of the right- 
handed acid exerted a right-handed rotation upon the plane of polarisation, which 
was turned in the opposite direction by a solution of the left-handed acid. 

The former acid has been named dextro-tartaric acid, and is the usual form in 
which this acid is met with ; the other acid has been called' lsevo-tartaric acid. In 
their chemical relations these acids are perfectly identical ; for the chemist they are 
both the same tartaric acid, equally well adapted for all the uses to which this acid 
is applied. 

Pasteur found that the double racemate of sodium and ammonium furnished a crop 
of crystals containing both right-handed and left-handed hemihedral forms, and on 
separating them by hand, he found that the action of their solutions on polarised 
light corresponded with their hemihedrism, and on isolating the acids, the right- 
handed crystals furnished dextro-tartaric, the left-handed, lsevo-tartaric acid. 

This analysis of racemic acid was soon confirmed by its synthesis. On mixing 
concentrated solutions of equal parts of dextro-tartaric and lsevo -tartaric acids, a 
considerable rise of temperature was observed, showing that combination had taken 
place, and the solution, which had no longer the power of rotating the plane of 
polarisation, furnished crystals of racemic acid. 



CITKIC ACID — MALIC ACID. 591 

This remarkable instance of chemical combination between two acids which are, 
in their chemical properties, perfectly identical, to furnish a new acid differing from 
both, affords, by analogy, some support to the theory of the duplex constitution of 
many elementary and compound bodies. 

417. Citric acid (C 6 H 8 7 ) occurs in lemons, oranges, and most acidulous 
fruits. It is prepared from lemon-juice, which contains the acid in a free 
state, by neutralising it with chalk, when calcium citrate (Ca 3 2C 6 H 5 O r ) 
is obtained, which is decomposed by dilute sulphuric acid; the filtered 
solution, when evaporated, yields prismatic crystals of citric acid, which 
contain C 6 H 8 7 .Aq. They fuse at 212° F., and lose the water of crystal- 
lisation. From the formula of calcium citrate, it will be seen that citric 
acid is tribasic, and should be written H 3 C 6 H 5 O r ; hence, like ordinary 
phosphoric acid, it forms three series of salts. The citrates of sodium, for 
example, have the composition, 2(Na 3 C 6 H 5 Q 7 ),llAq., Na 2 HC 6 H 5 7 .Aq., 
NaH 2 C 6 H 5 O r .Aq. When citric acid is heated above 300° F., it is con- 
verted into aconitic acid (H 3 C 6 H 3 6 ), another vegetable acid found in the 
different varieties of monkshood (aconitum). 

Citric acid is employed in dyeing and calico-printing, as well as in 
medicine. 

By fermentation in contact with yeast, calcium citrate is converted into acetate 
and butyrate of calcium, with evolution of carbonic acid gas and hydrogen. The 
crude calcium citrate prepared in Sicily, and imported for the preparation of the acid, 
is found sometimes to undergo this change spontaneously, so that it has been recom- 
mended to neutralise the hot lemon-juice with magnesium carbonate (which is 
abundant in Italy), when the tribasic magnesium citrate is precipitated in minute 
crystals. By dissolving this precipitate in a fresh quantity of hot lemon-juice, and 
evaporating, "the bibasic magnesium citrate is obtained in crystals, which is recom- 
mended as the best form in which to import the acid into this country. 

418. Malic acid (H 2 C 4 H 4 5 ) is a crystalline -acid found, as its name 
implies, in apples and many other fruits. It is present, together with 
oxalic acid, in rhubarb. Tobacco leaves also contain it in the form of 
calcium bimalate, CaH 2 2C 4 H 4 5 . 

In order to extract the malic acid from rhubarb stalks, it is converted into calcium 
malate, the solubility of which enables it to be separated from the insoluble citrate 
and tartrate of calcium. The juice is squeezed out of the stalks by a press, nearly 
neutralised with slaked lime suspended in water, and calcium" chloride is added. 
The precipitate containing tartrate, citrate, phosphate, and oxalate of calcium, is 
filtered off, and the liquid boiled down, when calcium malate (CaC 4 H 4 5 ) is sepa- 
rated, together with some calcium citrate. This is washed and added to hot nitric 
acid, diluted with ten measures of water, as long as it continues to be dissolved. On 
cooling, bimalate of calcium is deposited, which is dissolved in water and decomposed 
by lead acetate, when it gives a curious precipitate of lead malate (PbC 4 H 4 5 .3Aq.), 
which becomes crystalline on standing, and fuses in the liquid below the tempera- 
ture of boiling water. By suspending the lead malate in water, and decomposing 
it with hydrosulphuric acid, the lead is separated as sulphide, and a solution of 
malic acid is obtained, which gives deliquescent prismatic crystals of the acid when 
evaporated to a syrup and set aside. Malic acid is decomposed by heat into two 
isomeric acids, the malceic and fumaric H 2 C 4 H 2 4 ; the latter is found in the plant 
known as fumitory (Fumaria officinalis). 

An excellent source of malic acid is the juice of the unripe berries of 
the mountain ash, in which it is accompanied by a volatile oily acid of 
pungent aromatic odour ; this has been called parasorbic acid, and has 
the formula HC 6 H r 2 . When fused with potash, or boiled with a strong 
mineral acid, it suffers a remarkable conversion into a crystalline solid 
acid, having precisely the same composition, called sorbic acid. 



592 TANNIC ACID. 

Under the influence of yeast in the presence of water, calcium malate 
is converted into succinate and acetate of calcium — 

3(H 2 C 4 H 4 5 ) = 2(H 2 C 4 H 4 4 ) + HC ? H 3 2 + 2C0 2 + H 2 0. 

Malic acid. Succinic acid. Acetic acid. 

The amide of malic acid, nialamide, C 4 H 8 N 2 3 , ammonium malate 
(NH 4 ) 2 C 4 H 4 5 minus 2H 2 0, has attracted some attention, because it has 
the same composition as asparagine, a crystalline substance extracted 
from the juice of the asparagus, marsh-mallow root, and some other plants ; 
but it is not identical with it, though asparagine, when acted on by 
nitrous anhydride, yields malic acid — 

C 4 H 8 N 2 3 + X 2 3 = H 2 C 4 H 4 5 4- H 2 + N 4 . 

Asparagine. Malic acid. 

.Asparagine is really the amide of another acid, the aspartic, into the 
ammonium-salt of which it becomes converted when heated for some time 
with water; C 4 H 8 ¥ 2 3 + H 2 = (NH 4 )C 4 H 6 NO, 

Asparagine. Ammonium aspartate. 

419. Tannic acid or tannin (C 27 H 22 O l7 ), the astringent principle of 
gall-nuts, from which it may be extracted by water, is characterised by 
two very useful properties, viz., by yielding a black precipitate with 
the salts of peroxide of iron, and by forming a tough insoluble compound 
with gelatine and gelatinous membrane, the first being turned to account 
in the preparation of ink, and the second in that of leather. 

For the preparation of ink, three quarters of a pound of bruised nut- 
galls are digested in a gallon of cold water, and 6 ounces of green vitriol 
(sulphate of iron) are added, together with 6 ounces of gum, and a few 
drops of kreasote. The mixture is set aside for two or three weeks, being 
occasionally agitated, and the ink afterwards poured off from the undis- 
solved part of the nut-gall. 

Pure ferrous sulphate (FeS0 4 ) and tannic acid might be mixed without 
change ; but when the mixture is exposed to the air, oxygen is absorbed, 
converting the ferrous into a ferric salt which forms a black precipitate of 
ferric tannate, the exact composition of which is not known. The gum 
is added to render the liquid viscous, so as to prevent the subsidence of . 
the black precipitate, and the kreasote prevents the ink from becoming 
mouldy. The brown colour of the ink in old manuscripts is due to the 
tannic acid having been partly removed by oxidation, leaving the brown 
ferric oxide ; the stain of iron-mould left by ink on linen after washing is 
due to the entire removal of the tannic acid by the alkali in the soap. 

Tanning.' — When infusion of nut-galls is added to a solution of gelatine, 
the latter combines with the tannic acid, and a bulky precipitate is 
obtained. If a piece of skin, which has the same composition as gelatine, 
be placed in the infusion of nut-galls, it will absorb the whole of the 
tannic acid, and become converted into leather, which is much tougher 
than the raw skin, less permeable by water, and not liable to putrefaction. 

The first operation in the conversion of hides into leather, after they 
have been cleansed, consists in soaking them for three or four weeks in 
pits containing lime and water, which saponifies the fat, and loosens the 
hair. The same object -is sometimes attained by allowing the hides to 
enter into putrefaction, when the resulting ammonia has the same effect as 
the lime. The loosened hair having been scraped off, the hides are soaked 
for twelve . hours in water containing y^^th of sulphuric acid, which 



TANNING. 593 

removes adhering lime, and opens the pores of the skin, so as to fit it to 
receive the tanning liquid. 

The tanning material generally employed for hides is the infusion of 
oak bark, which contains querci-tannic acid,, very similar in properties to 
tannic acid. The hides are soaked in an infusion of oak bark for about 
six weeks, being passed in succession through several pits in which the 
strength of the infusion is gradually increased. They are then packed in 
another pit with alternate layers of coarsely-ground oak bark; the pit is 
filled with water and left at rest for three months, when the hides are 
transferred to another pit, and treated in the same way; but, of course, the 
position of the hides will be now reversed — that which was uppermost, 
and in contact with the weakest part of the tanning liquor, will now be 
at the bottom. After the lapse of another three months the hide is gene- 
rally found to be tanned throughout, a section appearing of a uniform 
brown colour. It has now increased in weight from 30 to 40 per cent. 
The chemical part of the process being now completed, the leather is sub- 
jected to certain mechanical operations to give it the desired texture. For 
tanning the thinner kinds of leather, such as morocco, a substance called 
sumach is used, which consists of the ground shoots of the Rhus Coriaria, 
and contains a large proportion of tannic acid. 

Morocco leather is made from goat and sheep skins, which are denuded 
of hair by liming in the usual way, but the adhering lime is afterwards 
removed by means of a bath of sour bran or Hour. In order to tan the 
skin so prepared, it is sewn up in the form of a bag, which is filled with 
infusion of sumach, and allowed to soak in a vat of the infusion for 
some hours. A repetition of the process, with a stronger infusion, is 
necessary ; but the whole operation is completed in twenty-four hours. 
The skins are now washed and dyed, except in the case of red morocco, 
which is dyed before tanning, by steeping it first in alum or chloride of 
tin, as a mordant, and afterwards in infusion of cochineal. Black 
morocco is dyed with acetate of iron, which acts upon the tannic acid. 
The aniline dyes are now much employed for dyeing morocco. 

The kid of which gloves are made is not actually tanned, but sub- 
mitted to an elaborate operation called tawing, the chief chemical features 
of which are the removal of the excess of lime,* and opening the pores of 
the skin by means of a sour mixture of bran and water, in which lactic 
acid is the agent ; and the subsequent impregnation of the porous skin 
with aluminium chloride, by steeping it in a hot bath containing alum 
and common salt. The skins are afterwards softened by kneading in a 
mixture containing alum, flour, and the yolks of eggs. The putrefaction 
of the skin is as effectually prevented by the aluminium chloride as by 
tanning. 

Wash-leather and ouckskin are not tanned, but shamoyed, which con- 
sists in sprinkling the prepared skins with oil, folding them up, and 
stocking them under heavy wooden hammers for two or three hours. 
When the grease has been well forced in, they are exposed in a warm 
atmosphere, to promote the drying of the oil by absorption of oxygen 
(page 583). These processes having been repeated the requisite number of 
times, the excess of oil is removed by a weak alkaline bath, and the skins 
are dried and rolled. The buff colour of wash-leather is imparted by a 
weak infusion of sumach. 

* Polysulphides of sodium and calchim are sometimes employed for removing the hair. 

2 P 



594 GALLIC ACID. 

Parchment is made by stretching lamb or goat skin upon a frame, re- 
moving the hair by lime and scraping, as usual, and afterwards rubbing 
with pumice stone, until the proper thickness is acquired. 

Tannic acid, like many other proximate constituents of vegetables 
(see page 482), when boiled with diluted sulphuric acid, yields glucose, 
whilst a new acid may be obtained from the solution, which is known as 
gallic acid ■ * C 27 H 22 17 + 4H 2 = 3(C 7 H 6 5 ) + C^H^ 

Tannic acid. Gallic acid. Glucose. 

The addition of dilute sulphuric acid to the infusion of gall-nuts pro- 
duces a precipitate composed of tannic and sulphuric acid, but this 
dissolves when boiled with excess of sulphuric acid, suffering the above 
change. 

According to Schiff, pure tannic acid does not yield glucose when boiled with 
sulphuric acid. He regards tannic acid as digallic acid (C 7 H 5 4 ) 2 0, of which natural 
tannin is a glucoside, its decomposition under the action of sulphuric acid being 
represented by C :}4 H 28 O 22 + 2H 2 O = C 6 H 12 O 6 + 2C 14 H 10 O 9 
Tannin. ~ Glucose. Digallic acid. 

The digallic acid is monobasic, its salts being formed upon the type HC 14 H 9 9 . 

420. Gallic acid (H 3 C 7 H 3 5 ) is also formed from tannic acid when 
exposed to the air, particularly in the presence of the matters associated 
with it in the gall-nut. The method generally practised for obtaining 
gallic acid consists in exposing powdered nut-galls in a moist state to the 
action of the air for some weeks, in a warm place, when oxygen is absorbed, 
and carbon dioxide evolved, the powder becoming covered with crystals of 
gallic acid (tannic acid does not crystallise). By boiling the mass with 
water, the gallic acid is extracted, and since, unlike tannic acid, it is very 
sparingly soluble in cold water, the greater portion crystallises out as the 
solution cools, in long silky needles, containing C 7 H 6 5 .Aq. 

In this process another acid is obtained in small quantity, which is 
insoluble in water, and has been called ellagic acid (HC 7 H 2 4 ) ; it 
possesses some interest, because it is found as a product of animal life in 
certain intestinal concretions or bezoars, occurring in the antelopes of 
Central Asia. It may be extracted by alcohol from the tanning material 
called divi-divi (the pods of Ccesalpina coriaria). 

According to Schiff, gallic acid is C 7 H 5 4 .OH, and may be converted into tannic 
(digallic) acid by boiling its alcoholic solution with arsenic acid, which undergoes no 
change in the process; 2(C 7 H 5 4 .OH) = (C 7 H 5 4 )2° + H 2 . 
Gallic acid.' Digallic or tannic acid. 

He regards ellagic acid as H 2 0. C ]4 H s 9 . By heating gallic and arsenic acids together 
in solution for some time, ellagic acid is obtained as a crystalline precipitate — 

4C 7 H 6 5 + As 2 5 = 2C 14 H ]0 O ]0 + As 2 3 + 2H 2 . 
Gallic acid. Ellagic acid. 

It may also be obtained by heating tannic acid with arsenic anhydride — 

2C 14 H 10 O 9 + As 2 5 = 2C 14 H 10 O 10 = As 2 3 . 
Tannic acid. 

"When an alkaline solution of gallic acid is exposed to air, it absorbs oxj^gen and 
acquires a dark colour due to taunomclanic acid, C 6 H 4 3 , which appears also to be 
produced by the action of nitrous acid on gallic acid. 

In most astringent substances a small quantity of gallic acid accom- 
panies the tannic. 

* It will be perceived that tannic acid is analogous in constitution to the gluco-tartaric 
acid mentioned at p 579, which splits into glucose and tartaric acid when boiled with 
diluted sulphuric acid, exactly as tannic acid splits into glucose and gallic acid. 



GALLIC ACID. o9o 

Gallic acid dissolves in oil of vitriol with a reel colour, and when the 
solution is poured into water, a red-brown precipitate is obtained, called 
rufigallic acid (C 14 H 8 8 ), which is interesting from its property of dyeing 
calico red, if previously mordanted with alum. 

When powdered nut-galls are heated in an iron pan surmounted with 
a cone of paper (see benzoic acid, page 479) to about 420°, a quantity of 
crystals sublime into the cone, which are pyrogallic acid (C 6 H 6 3 ), or 
more properly, pyrogallin or pyrogallol, for it is doubtful whether it is 
really an acid substance. 

Its formation from the tannic acid of the galls is explained by the 
equation, C 2 ^H 22 O ir (Tannic acid) + H 2 = 4(C 6 H 6 3 ) (Pyrogallin) + 3C0 2 .* 
As its name implies, this acid may also be obtained by the action of heat 
upon gallic acid, which suffers a similar decomposition.! 

This substance is extensively prepared for use in photography, in which 
art its great tendency to absorb oxygen is called into play, rendering it 
capable of decomposing the salts of silver with immediate separation of 
the metal. To prepare solution of pyrogallol as a developer, Thorpe heats 
10 grammes of gallic acid with 30 c.c. of glycerine to 195° C. as long as 
C0 2 is evolved, and makes up to a litre with water. 

The solution of pyrogallin soon becomes brown when exposed to the 
air, from, absorption of oxygen, and if it be mixed with an alkali, it 
absorbs oxygen almost instantaneously, acquiring a very dark brown colour. 
This property renders pyrogallin very useful in the analysis of air 
and of other gases containing uncombined oxygen ; a portion of air 
confined in a graduated tube over mercury (see fig. 82) is shaken with 
a strong solution of potash to absorb carbonic acid gas, and the diminution 
of volume having been noted, some solution of pyrogallin in 4 parts of 
water is introduced; on shaking for a few s'econcls, the oxygen is 
entirely absorbed, when the volume of the nitrogen may be observed. 

The salts of tannic and gallic acids are not very well known. The 
latter appears to be a tribasic acid, so that its true formula would be 
H 3 C 7 H 3 5 , the H 3 being replaceable by a metal. The acid character of 
pyrogallic acid is very feeble. 

The three acids are distinguished by their action upon the salts of iron. 
With pure ferrous sulphate (FeS0 4 ) neither tannic or gallic acid gives 
any reaction, but pyrogallic acid gives a deep indigo blue solution; whilst 
with ferric sulphate (Fe 2 3S0 4 ) or chloride (Fe 2 Cl 6 ), the two former give a 
bluish-black precipitate, and pyrogallic acid gives a bright red solution. 

The presence of tannic acid in a vegetable infusion is easily recognised 
by the addition of ferric chloride, but the hue which is produced is not 
the same in all astringent substances, because they contain different 
varieties of tannin. All these varieties, however, differ from tannic acid 
properly so called, in not furnishing pyrogallin when heated. The 
astringent principle of catecliu {terra japonica or cutcli) and kino, which 
are used by tanners and dyers, is called mimotannic acid. 

Phloro-glucol, C 6 H 6 3 , which is isomeric with pyrogallol, is formed when gamboge, 
dragon's blood, and similar gum-resins are fused with potassium hydrate. It forms 

* Or, adopting Schiff s formula for tannic acid — 

2C 14 H ]0 O 9 + 2H 2 = 4C 6 H 6 3 + 4C0 2 . 
Tannic acid. Pyrogallin. 

+ By beating gallic acid under pressure witb two or tbree parts of water to 410° F. for 
half an hour, and evaporating the solution, it is said that the theoretical epiantity of pyro- 
gallic acid may be obtained. It may be decolorised with animal charcoal. 



596 COMPOSITION OF OPIUM. 

prismatic crystals, C 6 H 6 3 .2H 2 0, which dissolve in water, alcohol, and ether. Its 
solution gives a deep violet colour with ferric salts. 

VEGETABLE ALKALOIDS. 

421. In some plants the vegetable acids are combined with vegetable 
alkalies or alkaloids; thus in opium, the morphine is combined with 
meconic acid; in cinchona bark, the quinine is combined with kinic acid. 
The methods adopted for the separation of these alkaloids from the acids 
and other substances associated with them are among the most important 
processes of practical chemistry. 

Extraction of the alkaloids from opium. — Opium is the concrete milky 
juice which exudes on incising the unripe capsules of the Pajpaver somni- 
ferum, and is imported into this country from Persia, Turkey, Bengal, and 
Egypt, in the form of round masses or cakes enveloped in leaves ; it has a 
dark colour, a soft waxy consistence, and a peculiar characteristic odour. 
Different samples vary much in composition, but the following result of 
an analysis of Smyrna opium will give an idea of the nature of this com- 
plex drug : — 

100 parts of Smyrna Opium contained — ■ 



Gum, . . 


. 26-2 


Narceine, . . . .6*7 


Caoutchouc, 


. 6-0 


Meconine, . . . .0*8 


Eesin, 


. 3-6 


Codeine, . . . .07 


Oily matter, 
Meconic acid, . 


2-2 
. 5-0 


Colouring and other organic ) .„.. 
matters, . . . \ 


Morphine, 


. 10-8 


Water, . . . . 9'9 


Narcotine, 


. 6-8 





The medicinal value of opium appears to be due chiefly to the morphine 
(C l7 H 19 ]Sr0 3 ), which is present, for the most part, in the state of meconate ; 
in order to obtain it in the separate state, the opium is cut into slices and 
digested with water at a moderate heat for two or three hours; the liquor 
is then strained and evaporated, a little chalk being added to neutralise 
the free acid. The concentrated solution, containing chiefly morphine 
and codeine, in combination with meconic and sulphuric acids, is mixed 
with solution of calcium chloride, when the meconic acid is precipitated as 
calcium meconate, carrying with it a great part of the colouring matter, 
and leaving in solution the hydrochlorates of morphine and codeine, 
which may be obtained in crystals by evaporation. The hydrochlorates 
are decolorised with animal charcoal and recrystallised. On adding am- 
monia to the solution containing these salts, the morphine only is pre- 
pitated, and may be purified by crystallisation from alcohol, whi^h deposits 
it in white rectangular prisms, having the formula- Cj^H^NOg-Aq. 

The solution from which the morphine has been precipitated still con- 
tains the codeine hydrochlorate, and on decomposing it with potash, the 
codeine is precipitated in crystals, of the composition C 18 II 21 ]TO 3 .Aq. 

The mother-liquor from the hydrochlorates of. morphine and codeine 
contains narcotine, narceine, meconine, thebaine, papaverine, and some 
other alkaloids, together with resin and colouring matter.* 

The leading features oi morphine are its sparing solubility in cold water, 
its bitter taste and alkaline reaction, and narcotic poisonous properties. 
It is generally identified by its giving an inky blue colour with ferric 

* Ka>06ia, a poppy head ; vapK\], torpor ; finKwv, a povpy. 



EXTRACTION OF QUININE. 597 

chloride, and a golden yellow with nitric acid. The yellow colour 
appears to be due to an acid having the composition C 10 H 9 NO 9 , which 
yields picric acid when heated with water to 100° C. in a sealed tube. 

The morphine liydrochlorate (C^H^JSTOg.HCl), or muriate of morphia, 
is the chief form in which this alkaloid is used medicinally. 

When morphine liydrochlorate is heated with hydrochloric acid to 150° C. for some 
hours, it loses the elements of water, and is converted into the liydrochlorate of 
apomorphine C 17 H 17 N0 2 , which is remarkable for its emetic properties. Morphine 
has been converted into codeine C 17 H 18 (CH 3 )N0 3 by heating it with sodium hydrate 
and methyle iodide in alcoholic solution. 

Narcotine (C 22 H 23 N"0 7 ) possesses some interest as having been the first 
base extracted from opium, whence it may be obtained by simply treating 
the drag with ether, in which the morphine is insoluble. The greater 
part of the narcotine is left in the residue after exhausting the opium 
with water, from which it is extracted by digestion with acetic acid ; on 
neutralising the solution with ammonia, narcotine is precipitated. It is 
a weak base, and has no alkaline reaction. 

The meconic acid which exists in opium is a tribasic acid, having the 
formula H 3 C 7 H0 7 ; it is soluble in hot water, and crystallises on cooling 
in plates which contain 3 molecules of water of crystallisation. It 
gives a blood-red colour with solution of ferric chloride. 

422. Extraction of quinine. — The cinchona or Peruvian bark, so highly 
prized for its medicinal qualities, is obtained chiefly from the districts 
around the Andes, and is imported in three varieties, of which the yellow 
cinchona is richest in quinine, the pale or grey bark in cinchonine, whilst 
the red bark contains both these bases in considerable quantity. The 
alkaloids are combined with kinic acid, and with a variety of tannin 
known as quinotannic acid. 

In order to extract them, the bruised bark is boiled with diluted 
hydrochloric acid, and the filtered solution, containing the hydrochlorates 
of quinine and cinchonine, is mixed with enough lime diffused through 
water to render it alkaline. The quinine and cinchonine, which are very 
sparingly soluble in cold water (requiring about 400 times their weight to 
dissolve them), are precipitated together with some of the colouring matter 
of the bark. 

The precipitate having been collected upon a linen strainer and strongly 
pressed, is treated with boiling alcohol, which dissolves both the alkaloids, 
leaving any excess of lime undissolved. A part of the alcohol is then 
recovered by distillation, and the solution containing the quinine and 
cinchonine is neutralised with sulphuric acid, so as to convert the alkaloids 
into sulphates, and is then decolorised with animal charcoal, and allowed to 
crystallise. Quinine sulphate, being much less soluble in water than 
cinchonine sulphate, crystallises out first, leaving the latter in solution. 
The quinine sulphate is dissolved in water and decomposed by ammonia, 
when the quinine is separated as a white powder, which may be dissolved 
in alcohol and crystallised. 

The liquid from which the quinine sulphate has been deposited con- 
tains, in addition to cinchonine sulphate, another base having the same 
composition as quinine, but distinguished from it by the indisposition of 
its sulphate to crystallise. This base is termed quinidine, and is produced 
from quinine under the influence of an excess of acid; it is the most 



5y» THEINE OR CAFFEINE. 

important constituent of the substance called quinoidine or amorphous 
quinine, which is prepared for sale from the mother-liquors of quinine 
sulphate, and forms a cheap substitute for quinine in medicine. 

Quinamine, C 19 H 24 ]Sr 2 2 , is also found in the quinine mother-liquors. 

Quinine crystallises in small prisms, which have the composition 
C 20 H 24 N 2 O 2 .3Aq. or Q.3Aq.,'and although sparingly soluble, even in boiling 
water, it has an extremely bitter taste, which is also possessed by its salts. 
It is used in medicine in the form of basic sulphate, Q. 2 H 2 S0 4 .7Aq., 
which requires as much as 700 parts of cold water to dissolve it, but is 
readily dissolved in water acidulated with sulphuric acid, when it is 
converted into the normal sulphate of quinine (Q.H 2 S0 4 ) (or, with 
another atom of acid, into the acid sulphate). The solution is remarkable 
for its action upon light, for although it is perfectly colourless when held 
directly in front of the eye, if seen obliquely it appears to have, especially 
at the edge, a beautiful pale blue colour. This phenomenon, which is 
termed fluorescence, has been already referred to in the case of other 
substances (page 485). 

Quinic or hinic acid. — By evaporating the infusion of cinchona bark 
from which the quinine and cinchonine have been separated by lime, 
crystals of calcium quinate are obtained, and on decomposing these with 
sulphuric acid, the quinic acid (HC 7 H 11 6 ) passes into solution, whence it 
may be obtained in prismatic crystals. 

This acid is chiefly interesting on account of the peculiar properties 
of some of its derivatives. When distilled with sulphuric acid and 
manganese dioxide, the oxygen evolved from the mixture converts the 
quinic acid into a new substance, which condenses in beautiful yellow 
needles called kinone or quinone; HC^Hj x O Q + 2 = C 6 H 4 2 + C0 2 + 4H 2 0. 

Quinic acid. Quinone. 

The same substance is obtained in a similar manner from one of the 
constituents of the coffee-berry (caffeic or caffeotannic acid). By dissolving 
quinone in water containing sulphurous acid, and evaporating the solution, 
colourless crystals of hydroquinone are obtained — 

C 6 H 4 2 +* H 2 + H 2 S0 3 = C 6 H 6 2 + H 2 S0 4 . 

Quinone. Hydroquinone. 

When a solution of quinone is mixed with one of hydroquinone, beauti- 
ful green crystals are deposited, which are known as green liydroquinone 
(C 6 H 4 2 .C 6 H 6 2 ), and may also be obtained by the action of oxidising 
agents, such as ferric chloride, upon hydroquinone. When quinone is 
acted on with hydrochloric acid and potassium chlorate, it is converted into 
a yellow crystalline body, known as perchloroliinone or chloranile (C 6 C1 4 2 ), 
which is also obtained in a similar way from aniline, salicine, and isatine. 
Potash dissolves it when heated, giving a purple solution. 

423. Theine or Caffeine — Tea — Coffee. — A very remarkable instance of 
the application of chemistry to explain the use of widely different articles 
of diet by different nations, with a view to the production of certain 
analogous effects upon the system, is seen in the case of coffee, tea, Para- 
guay tea, and the kola nut (of Central Africa), which are very dissimilar 
in' their sensible properties, and afford little or no gratification to the 
palate, owing what attractions they possess chiefly to the presence, in 
each, of one and the same active principle or alkaloid, which has a 
special effect upon the animal economy. This alkaloid is known as 
caffeine or theine, and is associated in the three articles of diet men- 



. COFFEE — TEA. 59 § 

tioned above, with various substances, which give rise to their diversity 
in flavour. 

The raw coffee-berry presents, on the average, the following composi- 
tion: — 

100 parts of Raw Coffee contain — 

Woody fibre, 34*0 

Water, . . . 12*0 

Fat, . 12 

Cane-sugar and gum, . . . . . . 15 '5 

Legumine, or some allied substance, . . . . 13 "0 

Caffeine, . . . . . . . . . . 1 "5 

Caffeic acid, ......... 4*0 

Mineral substances, ........ 7 '0 

When the raw berry is treated with hot water, the infusion, which con- 
tains the sugar and gum, the legumine, caffeine, and caffeic acid (C 9 H 8 4 ), 
has none of the peculiar fragrance which distinguishes the ordinary 
beverage, and is due to an aromatic volatile oily substance termed caffeol 
(C 8 H 10 O 2 ) formed during the roasting to which the berry is subjected 
before use. This volatile oil, which is present in very minute quantity, 
is produced from one of the soluble constituents of the berry (probably 
from the caffeic acid), for if the infusion of raw coffee be evaporated to 
dryness, the residue, when heated, acquires the characteristic odour of 
roasted coffee. 

Acetic and palmitic acids are also found among the products of coffee- 
roasting. 

The roasting is effected in ovens at a temperature rather below 400° F., 
when the berry swells greatly, and loses about ^tk of its weight, becoming 
brittle, and easily ground to powder. It also becomes very much darker 
in colour, from the conversion of the greater part -of its sugar into caramel 
(page 505), which imparts the dark brown colour to the infusion of coffee. 
If the roasting be carried too far, a very disagreeable flavour is imparted 
to the coffee by the action of heat upon the legumine and other nitro- 
genised substances contained in the berry. 

From 100 parts of the roasted coffee, boiling water extracts about 20 
parts, consisting of caffeine, caffeic acid, caramel, legumine, a little sus- 
pended fatty matter, fragrant volatile oil (caffeone), and salts of potassium 
(especially the phosphate). The undissolved portion of the coffee contains, 
beside the woody fibre, a considerable quantity of nitrogenised (and nutri- 
tious) matter, and hence the custom, in some countries, of taking this 
residue together with the infusion. 

In order to extract the caffeine from the infusion of coffee, it is mixed 
with solution of tribasic lead acetate, to precipitate the caffeic acid and 
a part of the colouring matter. Through the filtered solution sulphuretted 
hydrogen is passed to remove the lead as sulphide, and the liquid filtered 
from this is evaporated to a small bulk, when the caffeine crystallises out 
in white silky needles, which have a bitter taste, and the composition 
C 8 H 10 N 4 O 2 .H 2 O. Its basic properties are very feeble. 

The constituents of the leaves of the tea-plant (Thea sinensis) exhibit a 
general similarity to those of the coffee-berry. In the fresh leaf we find, 
in addition to the woody fibre, a large quantity of a substance containing 
nitrogen, similar to legumine, an astringent acid similar to tannic acid, a 
small quantity of caffeine, and some mineral constituents. 

The aroma of tea does not belong to the fresh leaf, but is produced, like 



600 COCOA— STRYCHNINE. 

that of coffee, during the process of drying by heat, which develops a 
small quantity of a peculiar volatile oil, having powerful stimulating pro- 
perties. The freshly dried leaf is comparatively so rich in this oil that 
it is not deemed advisable to use it until it has been kept for some time. 

Green and black tea are the produce of the same plant, the difference 
being caused by the mode of preparation. For green tea the leaves are 
dried over a fire as soon as they are gathered, whilst those intended for 
black tea are allowed to remain exposed to the air in heaps for several 
hours, and are then rolled with the hands and partially dried over a fire, 
these processes being repeated three or four times to develop the desired 
flavour. The black colour appears to be due to the action of the air upon 
the tannin present in the leaf. 

Boiling water extracts about 30 parts of soluble matter from 100 of 
black tea, and 36 from 100 of green tea. The principal constituents of 
the infusion of tea are tannin, aromatic oil, of which green tea contains 
about 0'8 and black tea 0*6 per cent., and caffeine, the proportion of 
which, in the dried leaf, varies from 2*2 to 4*1 per cent., being present in 
larger quantity in green tea. 

The spent leaves contain the greater part of the legumine and a con- 
siderable quantity of caffeine, which may be extracted by boiling them 
with water, and treating the decoction as above recommended in the case 
of coffee. 

If tea be boiled with water, the solution precipitated with tribasic 
lead acetate, the filtered liquid evaporated to dryness, and the residue 
cautiously heated, the caffeine sublimes in beautiful crystals. 

Cocoa and chocolate are prepared from the cacao-nut, which is the 
seed of Theobroma Cacao, and is characterised by the presence of more 
than half of its weight (minus the husk) of a fatty substance known as 
cacao-butter, and consisting of oleine and stearine, which does not become 
rancid like the natural fats generally. The cacao-nut also contains a 
large quantity of starch, a nitrogenised substance resembling gluten, to- 
gether with gum, sugar, and theobromine, a feeble base very similar to 
caffeine, but having the composition CfH 8 N 4 2 . 

The seeds are allowed to ferment in heaps for a short time, which 
improves their flavour, dried in the sun and roasted like coffee, which 
develops the peculiar aroma of cocoa. The roasted beans having been 
crushed and winnowed to separate the husks, are ground in warm mills, 
in which the fatty matter melts and unites with the ground beans to a 
paste, which is mixed with sugar and pressed into moulds. In the pre- 
paration of chocolate, vanilla and spices are also added. 

From the composition of cocoa and chocolate it is seen that when con- 
sumed, as is usual, in the form of a paste, they would prove far more 
nutritious than mere infusions of tea and coffee. 

Caffeine appears to be a methylated derivative from theobromine, for when it is 
boiled with potash, methylamine is evolved, and by acting with methyle iodide 
(CH 3 I) upon a silver compound obtained from theobromine, C 7 (H 7 Ag)N 4 2 , the 
silver and methyle change places, yielding Agl and caffeine, C 7 H 7 (CH 3 )N 4 2 or 
methyle-theobromine. 

424. The vegetable alkali strychnine (C 21 H 22 N 2 2 ), only too well known 
for its activity as a poison, is contained in crow-Jig or Nux-vomica, the 
seed of the poison nut tree of the East Indies, and in several other plants 
of the same family. The strychnine appears to be combined, in the nux- 



TOBACCO. 601 

vomica, with lactic acid, and is accompanied by a second alkaloid, Urucine 
(C 23 H 26 N 2 4 ). In order to extract it, the bruised seeds are boiled with 
water acidulated with hydrochloric acid, the solution is strained, and ren- 
dered alkaline by adding lime, which displaces the strychnine and brucine 
from their combination with the acid, and separates them in the form of 
a precipitate. When this is boiled with alcohol, the excess of lime re- 
mains undissolved, whilst the strychnine and brucine are carried into 
solution ; and since the former is less soluble in alcohol than the latter, 
it is deposited, before ihe brucine, on evaporating the liquid, in the 
form either of octahedral or prismatic crystals, which have an intensely 
bitter taste. This remarkable bitterness is one of the most prominent 
characters of strychnine ; for although 7000 parts of water are required 
to dissolve one part of the alkaloid, the solution possesses an intolerably 
bitter flavour, even when further diluted with 100 times its weight of 
water. Chloroform and benzene both dissolve strychnine with great ease ; 
and since these liquids refuse to mix with water, they are often employed 
to extract the poison from a large bulk of aqueous liquid by agitating it 
with a small quantity of one of them, which is then separated from the 
water and evaporated, in order to obtain the strychnine in the solid fonn. 
Very minute quantities may then be identified by moistening with strong 
sulphuric acid, and adding a miuute quantity of potassium chromate, when 
the chromic acid acts upon the strychnine, giving rise to products of oxida- 
tion, which pervade the liquid in the form of beautiful purple streaks. 

Curarine, C 10 H 15 ]N", is a crystalline alkaloid which has been extracted 
from the woorari or curara poison employed by the American Indians 
for poisoning arrows. It dissolves easily in water and alcohol, but not in 
ether. Strong sulphuric acid gives it a fine blue colour. 

425. Tobacco owes its active character chiefly to the presence of a vege- 
table alkali which is not found in any other plant than the Nicotiana taba- 
cum, from the leaf of which the various forms of tobacco are manufactured. 
This alkali, nicotine (C 10 H 14 N 2 ), is distinguished from most others by the 
absence of oxygen, and by its liquid condition at the ordinary temperature. 

In order to extract the nicotine from tobacco, the leaves are boiled with 
water, which dissolves the alkaloid, in combination with malic and citric 
acids. The liquid, having been strained, is evaporated to a syrup and 
mixed with alcohol, when it separates into two layers, of which the 
upper contains the salts of nicotine dissolved in alcohol, the lower aqueous 
layer retaining the greater part of the extraneous vegetable matters. The 
alcoholic layer having been drawn off, is next shaken with potash, to 
combine with the acids, and with ether to dissolve the nicotine then set 
free. On decanting the ethereal solution of nicotine which rises to the 
surface, and evaporating the ether, the nicotine is left in the form of an 
oily liquid, which is colourless when perfectly pure, but soon acquires a 
dark brown colour when exposed to the air. It is very, readily distin- 
guished by its very pungent, irritating odour, recalling that of tobacco, 
and which is very perceptible at the common temperature, although the 
boiling-point of nicotine is so high as 480° F. "Water, alcohol, and ether 
dissolve nicotine with facility. The poisonous action of this alkaloid upon 
animals is very powerful, death almost immediately following its adminis- 
tration. The Virginian tobacco contains more nicotine than other varieties, 
the alkaloid amounting, to nearly 7 per cent, of the weight of the leaf 



602 COLOURING, MATTEK OF PLANTS. 

dried at 212° F., whilst the Maryland and Havannah varieties contain 
only 2 or 3 per cent, of nicotine. Tobacco is remarkable for the very 
large amount of ash which it leaves when burnt, amounting to about one- 
fifth of the weight of the dried leaf, and containing about one- third of potas- 
sium carbonate, resulting from the decomposition of the malate, citrate, 
and nitrate of potassium, during the combustion. The presence of this 
latter salt in large quantity (3 or 4 parts in 100 of the dried leaf) distin- 
guishes tobacco from most other plants, and accounts for the peculiar 
smouldering combustion of the dried leaves. 

Cigars are made directly from the tobacco leaves, which are only mois- 
tened with a weak solution of salt in order to impart the requisite sup- 
pleness ; but snuff, after being thus moistened, is subjected, in large 
heaps, to a fermentation extending over eighteen or twenty months, which 
results in its becoming alkaline from the development of ammonium 
carbonate (by the putrefaction of the vegetable albumen in the leaf) and 
of a minute quantity of free nicotine, which imparts the peculiar pungency 
to this form of tobacco. The aroma of the snuff appears to be due to 
the production of a peculiar volatile oil during the fermentation. The 
proportion of nicotine in snuff is only about 2 per cent., being one-third 
of that found in the unfermented tobacco; and a great part of this exists 
in the snuff in combination with acetic acid, which is also a result of the 
fermentation. It is also not improbable that a little acetic ether is pro- 
duced, and perhaps some other acids and ethers of the acetic series {e.g., 
butyric and valerianic), of which extremely minute quantities would give 
rise to great differences in the aroma of the snuff. 

VEGETABLE COLOURING MATTERS. 

426. Notwithstanding the great variety and beauty of the tints ex- 
hibited by plants, comparatively few yield colouring matters which are 
sufficiently permanent to be employed in the arts ; the greater number of 
them fading rapidly as soon as the plant dies, since they are unable to 
resist the decomposing action of light, oxygen, and moisture, unless sup- 
ported by the vital influence in the plant; some of them even fading during 
the life of the plant, as may be seen in some varieties of the rose, which 
are only fully coloured in those parts which have been partly obscured. 

The green colouring matter of* plants has been termed chlorophyll* and 
is a resinous substance containing carbon, hydrogen, nitrogen, and oxygen, 
which has never yet been obtained in so pure a condition that its composi- 
tion could be accurately determined, since it cannot be crystallised or 
distilled, and is therefore not amenable to the usual methods by which 
organic substances are obtained in a pure state. 

AVhen green leaves are boiled with alcohol, the latter acquires a fine 
green colour, and, when evaporated, deposits the chlorophyll. When the 
alcoholic solution of chlorophyll is boiled with alcoholic solution of 
potash, and hydrochloric acid afterwards added, a yellow precipitate (phyl- 
loxanthine) is obtained, and a fine blue colouring matter (jihyllocyanine) 
remains in solution. The blue matter contains nitrogen, and both are 
insoluble in water. The autumnal colour of leaves may possibly be due 
to the dissappearance of the phyllocyanine. On immersing green leaves 
in chlorine they assume an autumnal tint. 

* XXwjOos, green; tyvWov, a leaf. 



COLOURING MATTER OF PLANTS. G03 

The blue colouring matter" contained in many flowers, such as the violet, 
has been named cyanine. Acids change its blue colour to red, and hence 
the blue colour is exhibited only by flowers the juice of which is neutral, 
whilst red flowers yield an acid juice. The colouring matter of grapes 
and of red wine appears to be identical with cyanine. 

Saffron is a yellow colouring matter obtained from the flowers of the 
Crocus sativus, which are themselves of a blue colour, but have yellow 
anthers. When these are dried and pressed into cakes, they form the 
saffron of commerce, which is characterised by its very remarkable and 
somewhat agreeable odour. The yellow colouring matter is readily dis- 
solved by water and alcohol, and has been found to be a glucoside, which 
yields, when treated with sulphuric acid, beside glucose, crocine, C 16 H 18 6 , 
and an essential oil having the formula C 10 H 14 O. 

Safflower consists of the petals of the Carthamus tinctorius, a plant 
cultivated in Egypt. It furnishes a red colouring matter called cartha- 
mine (C 14 H 16 7 ), which is used in dyeing, although it fades easily when 
exposed to light. It exhibits the characters of an acid, being dissolved 
by alkalies and reprecipitated by acids, a circumstance which is taken 
advantage of when extracting it from the safflower. 

The orange-yellow colouring matter known as annatto is extracted from 
the seeds of the Bixa Orellana, a native of the West Indies. The colouring 
principle has been called bixine, and is dissolved by alkalies, but precipi- 
tated again by acids. Annatto is used for colouring butter and cheese. 

A valuable yellow colour is obtained from the weld, or Reseda luteola, 
by boiling the dried leaves with water. This colouring matter is termed 
luteoline (C O0 H 14 O 8 ), and may be sublimed in yellow needles. 

The woods of various trees, when boiled with water, furnish colouring 
matters of considerable importance ; thus, the wood of Moras tinctoria, 
or fustic, a West Indian tree, yields a crystalline yellow colour called 
moritannic acid (C 13 H 16 6 .H 2 0). 

Logwood is the wood of the Hcematoxylon campecliianum, which grows 
at Cam peachy, in the Bay of Honduras. Its most important constitutent 
is a yellow colouring matter called licematoxyline, which may be obtained 
in needle-like crystals having the composition (C 16 H 14 6 .3Aq.). It becomes 
intensely red in contact with alkalies and oxygen, from the formation of 
hcematein (C 16 H 12 6 ). Potassium chromate gives an intense black colour 
with infusion of logwood, which has been used as an ink, but is not 
permanent. 

Brazil wood, which is employed in the preparation of red ink, contains 
brazilein (C 16 H 19 5 ), a colouring matter somewhat resembling that of 
logwood. 

The well-known Turkey red colour is obtained from madder, the root 
of the Rubia tinctorum, imported from the south of France and the 
Levant. This root does not contain any red colouring matter during the 
life of the plant, but a yellow substance (rubian, C 28 H 34 15 ), from the 
decomposition of which the madder red is obtained. There are several 
methods in use for obtaining the red colour from madder. If the root be 
steeped in water for some time, so that some of the nitrogenised con- 
stituents begin to undergo decomposition, a peculiar fermentation is excited 
in the rubian, resulting in its decomposition into several new bodies, the 
chief of which are a red crystalline colouring matter alizarine (C 14 H 8 4 ), 
and an uncrystallisable sugar. The alizarine may be dissolved out either 



604 PRODUCTION OF ARTIFICIAL ALIZARINE. 

"by water or alcohol, and may be obtained in beautiful plates having a 
golden lustre. 

If the madder root be boiled with water the rubian is dissolved, and 
when this solution is boiled with dilute sulphuric acid, the rubian under- 
goes a decomposition similiar to that mentioned above, and the alizarine, 
being insoluble in the dilute acid, is precipitated. 

Madder which has been treated with hot sulphuric acid, so as to decom- 
pose the rubian, is used in print-works under the name of garancine, and 
yields a red solution containing alizarine when boiled with water. 

Artificial alizarine.- — The discovery of a process for the artificial pro- 
duction of the colouring matter of madder from anthracene, one of the 
constituents of coal-tar, is one of the most important services which 
chemistry has, of late years, rendered to the useful arts, and affords an 
excellent illustration of the practical importance of the minute study of 
the constitution of organic substances. When alizarine, C 14 H 8 4 , was 
heated with powdered zinc, it was found to be converted into anthracene, 
C 14 H 10 , a substance obtained among the last products of the distillation 
of coal-tar, for which no useful application had hitherto been discovered.* 
It somewhat resembles naphthalene in properties, but may be dis- 
tinguished from it by its sparing solubility in alcohol. When treated 
with oxidising agents, such as a mixture of acetic and chromic acids, it 
yields a crystalline compound known as oxanthracene, C 14 H 8 2 , which 
bears the same relation to anthracene as quinone (page 598) (C 6 H 4 2 ) 
bears to benzene (C 6 H 6 ), and has therefore been called anthraquinone. 
When acted upon by bromine, this is converted into dibromantliraquinone, 
C 14 H 6 Br 2 2 . By heating this to about 350° F. with caustic potash, 
C 14 H 6 Br 2 2 + 4KHO = C 14 H 6 K 2 4 (jjotassic alizarate) + 2KBr + 2H 2 0. 
Alizarine is precipitated by decomposing the potassic alizarate with hvdro- 
chloricacid, C 14 H 6 K 2 4 + 2HC1 = C 14 H 8 4 {alizarine) + 2KC1. 

This reaction shows that alizarine is really dioxyanthraquinone, or anthraquinone 
in which 2 atoms of hydrogen are replaced by hydroxyle — 

Anthraquinone, C 14 H 8 2 ; Alizarine, C 14 H 6 (HO) 2 2 . 

Another colouring matter exists in madder, named imrpurine, having the formula 
C 14 H 5 (HO) 3 2 , or anthraquinone in which 3 atoms of hydrogen have been replaced 
by hydroxyle. In the process of preparing alizarine from anthracene, a red colouring 
matter is formed which has the same composition as the purpurine of madder, but 
differs from it in some of its properties ; this body has been called anthrapurpurine, 
and its presence in artificial alizarine greatly enhances the brilliancy of the reds 
obtained with this dye. 

Alizarine-orange, C 14 H 7 (N0 2 )0 4 , is obtained by the action of nitrous acid vapours 
upon dry alizarine. 

Within the last few years, the production of artificial alizarine has been conducted 
on a very large scale, and has materially reduced the importation of madder. The 
anthracene which crystallises out from the last runnings of the tar stills is purified by 
pressure and treatment with petroleum spirit. It is then distilled with a mixture of 
potashes with a little lime, by which certain impurities are decomposed, and the 
anthracene condenses in primrose-yellow crystalline cakes. 

Production of artificial alizarine from anthracene without previous conversion into 
anthraquinone. — The anthracene is exposed in leaden chambers to the action of 
chlorine gas, which converts it into a bright yellow crystalline mass of dichlor- 
anthracene ; C 14 H 10 + Cl 4 = C 14 H 8 C1 2 + 2HC1. The dichloranthracene is heated to 260° 
C. with strong sulphuric acid,in an iron pot, until a sample dissolves in water without 
fluorescence, when the following changes take place— 

* C l4 H 8 4 + H 2 + Zn 5 + 5ZnO = C 14 H 10 . 



C 14 H 6 (S0 3 H) 2 C1 2 + 


H 2 S0 4 


- C ]4 H 6 (S0 3 H) 2 2 

Disulphanthra- 
quinonie acid. 


Ci4H 8 Cl 2 + 


H 2 S0 4 


= C 14 H 8 2 + S0 2 

Anthraquinone. 


(4) C 14 H 8 2 + 


H 2 S0 4 


= C 14 H 7 (S0 3 H)0 2 

Sulphanthra- 
quinonic acid. 



CONVERSION OF ANTHRACENE INTO ALIZARINE. 605 

(1) C 14 H 8 C1 2 + 2H 2 S0 4 = C ?4 H fi (S0 3 H). 2 Cl 2 + 2H 2 0. 

Disulphodichloran- 
thracenic acid. 

+ S0 2 + 2HC1. 

+ 2HC1. 
+ HoO . 



The mixture of sulpho-acids is neutralised with slaked lirne, and the calcium 
salts are converted into sodium salts by treatment with sodium carbonate. The 
concentrated solution of the sodium salts is heated with caustic soda (and a little 
potassium chlorate), in a closed iron boiler, to about 180° C. for twenty-four hours, 
when a purple solution is obtained, containing the alizarate and anthrapurpurate of 
sodium — 

C 14 H 7 (HS0 3 )0 2 + 4NaHO = C 14 H 6 (NaO) 2 2 + N"a 2 S0 3 + 2H 2 + H 2 

Sodium alizarate. 

C 14 H 6 (HS0 3 ) 2 2 + 7XaHO = C 14 H 5 (NaO) 3 2 + 2Na 2 S0 3 + 4H 2 + H 2 . 

Sodium anthra- 
purpurate. 

The solution is run into dilute sulphuric acid in leaden tanks, when the artificial 
alizarine separates as a yellow precipitate consisting of a mixture of alizarine and 
authrapurpurine, which is washed and pressed — 

C a4 H 6 (NaO) 2 2 + 2H 2 S0 4 = C ]4 H 6 (HO) 2 2 + 2NaHS0 4 

Alizarine. 

C 14 H 5 (XaO) 3 2 + 3H 2 S0 4 = C ]4 H 5 (HO) 3 2 + 3XaHS0 4 . 
Anthrapurpurine. 

The potassium chlorate is added in order to oxidise some sodium oxanthraquinonate 
resulting from a secondary reaction — 

C 14 H 7 (NaO)0 + XaHO + = C 14 H 6 (NaO)o0 2 + H 2 0. 
Sodium oxanthra- Sodium alizarate . 

quinonate. 

Conversion of anthracene into anthraquinone and alizarine. — Anthracene is treated 
in leaden tanks with potassium dichromate and diluted sulphuric acid, the reaction 
being completed by boiling. The dichromate is converted into chrome alum, and the 
liberated oxygen changes the anthracene into anthraquinone, C 14 H 10 + O 3 = C 14 H 8 O o 
+ H 2 0. 

The anthraquinone is dissolved in strong sulphuric acid and reprecipitated by 
water, which retains the impurities in solution. After being washed and dried, it is 
heated for eight or ten hours to 180° C. with fuming sulphuric acid in an iron pot, 
being constantly stirred ; on diluting with water, any unaltered anthraquinone is 
precipitated, and sulphanthraquinonic acid remains in solution ; C ]4 H 8 2 + H 2 S0 4 
= C 14 H 7 (HS0 3 )0 2 + H 2 0. 

By neutralising this with caustic soda, the sparingly soluble sodium salt is obtained, 
which is converted into alizarine by heating with caustic soda and some potassium 
chlorate. 

The scientific interest of this production of alizarine from anthracene is 
enhanced by the circumstance that anthracene has itself been produced 
by synthesis ; for carbon and hydrogen combine, at a high temperature, 
to produce acetylene (C 2 H 2 ), 3 molecules of which coalesce at a high 
temperature to form benzene (C 6 H 6 ), and by acting upon 2 molecules of 
benzene with 1 molecule of ethylene, anthracene has been produced ; 
2C 6 H 6 -f- C 2 H 4 = C 14 H 10 + H 6 . 

Turmeric is the root of an East Indian plant, the Curcuma Tonga ; its 
yellow colouring matter, called curcumine (C 14 H 14 4 ), is nearly insoluble in 
water, but dissolves in alcohol. It is an acid body, forming red salts with 
the alkali metals, and is used in the laboratory as a test of alkalinity. 



606 COLOURING MATTERS PREPARED FROM LICHENS. 

427. Litmus, archil, and cudbear are brilliant, though not very per- 
manent purple and violet colours, prepared from various lichens, such as 
Roccella tinctoria (litmus), and Lecanora tartarea (cudbear).* 

Archil and cudbear owe their colour chiefly to the presence of orceine 
(C 7 H^0 3 ), which does not exist ready formed in any of the lichens, but 
is developed during the preparation which they undergo. 

If either of the above lichens be digested for some hours with lime and 
water and the filtered solution be neutralised with hydrochloric acid, a 
white gelatinous precipitate is obtained, which dissolves in hot alcohol, 
and is deposited in crystals on cooling. This substance may consist, 
according to the particular lichen employed, of one or more acids, the chief 
of which have been named erythric' (C 20 H 22 O 10 ), evernic (C l7 H 16 7 ), and 
lecanoric (C 16 H 14 0> r ) acids. These acids are remarkable for the facility 
with which they furnish compound ethers when boiled with alcohol. 

When either of these acids is boiled with an excess of lime or baryta, it 
is decomposed, and if the excess of base be removed by carbonic acid, the 
filtered liquid evaporated to a syrup, and extracted with boiling alcohol, 
the latter deposits prismatic crystals of orcine (C r H 8 2 .Aq.). The forma- 
tion of this body will be understood from the following equations — 

C 20 H 22 O 10 + 2Ca(HO) 2 = 2CaC0 3 -f 2C 7 H 8 2 + C 4 H 10 O 4 ; 

Erythric acid. Orcine. Erythrite. 

C ir H 16 O r -i- Ca(HO) 2 = CaC0 3 + C 9 Hi O 4 + C 7 H 8 2 

Evernic acid. Evernesic acid. Orcine. 

Pure orcine is a colourless substance, but when exposed to the joint action 
of ammonia and air, it is converted into a beautiful red colouring matter, 
orceine ; C 7 H 8 + NH 3 + 3 = C 7 H r N0 3 + 2H 2 0. 

Orcine. Orceine. 

Orceine does not crystallise, and dissolves to a slight extent only in water, 
but readily in alcohol and in alkaline liquids, yielding, in the latter 
case, a beautiful purple solution, which becomes red when mixed with 
acids, and deposits red flakes of orceine. 

The chemistry of the processes by which archil and cudbear are prepared 
will now be easily understood. The powdered lichen is mixed with urine 
(to furnish ammonia) and lime, and exposed to the air for some weeks, 
when the lime decomposes the erythric and other acids, with formation of 
orcine, which then passes into orceine under the influence of the ammonia 
and atmospheric oxygen. 

The preparation of litmus from the Rocella tinctoria is similar to that 
just described, but a mixture of carbonates of ammonium and potassium 
is employed instead of the urine and lime. The chemical change which 
takes place, although similar in principle, is not precisely identical 
with the foregoing, for the principal colouring matter developed appears 
to be a red substance called azolitmine (C 9 H 10 ~N"O 5 ), which differs from 
orceine by its insolubility in alcohol. It dissolves in alkaline solutions 
with a beautiful blue colour, which is immediately -reddened by acids, a 
property frequently turned to account by the chemist for detecting the acid 
reaction. Litmus occurs in commerce in small cakes, which are made up 
with chalk. 

Erythrite (C 4 H 10 O 4 ) is a crystalline substance extracted from various 
lichens and fungi, which forms combinations with the fatty acids similar 

* Said to have been named after Cuthbert, a manufacturer of the dye. 



BLUE INDIGO. ' 607 

to those formed by glycerine. It is sometimes represented as a tetratomic 
alcohol (page 565), (C 4 H 6 ) iv (HO) 4 . 

428. Indigo blue (C 16 H 10 N 2 O 2 )* is prepared from various species of 
Indigofera, grown in China, India, and America. The plants are covered 
with cold water, and allowed to ferment ; as soon as a blue scum appears 
upon the surface, a little lime is added and the mixture stirred briskly for 
some time, when the indigo is deposited in a pulverulent form; it is 
collected on calico strainers, pressed, and cut up into cakes. 

The theory of the process is not yet clearly explained; it is certain that 
the indigo blue does not pre-exist in the plant, but is a product of the 
fermentation. Recent observations have shown that the indigo plants 
probably contain a substance called indican (C 26 H 33 N0 18 ), which stands 
in a similar relation to indigo blue to that in which rubian stands to 
alizarine (in the case of madder) ; it is soluble in water, and when heated 
with an acid, splits up into indigo blue, indigo red, and a peculiar uncrystal- 
lisable sugar. The indigo red may be extracted from commercial indigo 
by boiling with alcohol, in which the indigo blue is insoluble. Since 
indigo blue is insoluble in all ordinary solvents, it is necessary, in order to 
use it for dyeing, to reduce it to* the condition of white indigo, which is 
soluble in alkalies. 

If 2 parts of ferrous sulphate (copperas) be dissolved in 200 parts of 
water, and well shaken in a stoppered bottle with 1 part of powdered 
indigo and 3 of slaked lime, the indigo will disappear, and on allowing 
the precipitate to subside, a yellow fluid will be obtained, which becomes 
blue at the surface as soon as it is exposed to air. If this solution be 
mixed with hydrochloric acid, out of contact with air, a flocculent pre- 
cipitate of ivliite indigo is obtained. The composition of this substance 
is C 16 H 12 TsT 2 2 , and it is formed from blue indigo (C 16 H 10 N 2 O 2 ) by the 
addition of 2 atoms of hydrogen derived from water, the oxygen of 
which has converted the ferrous hydrate into ferric hydrate ; one por- 
tion of the lime combines with the sulphuric acid of the ferrous sulphate, 
whilst another serves to dissolve, the white indigo, which is soluble in 
alkaline liquids ; FeS0 4 + Ca(OH) 2 = CaS0 4 + Fe(OH), ; 2Fe(OH), 
+ 2H 2 + C 16 H 10 X 2 O 2 = C 16 H 12 £T 2 2 * Fe 2 (OH) p . 

The solution. of white indigo prepared by this process is- employed for 
dyeing linen and cotton, which are immersed in the vat, and then exposed 
to the air, the oxygen of which removes two atoms of hydrogen from the 
white indigo, and the blue indigo thus formed is precipitated upon the 
fibre. 

Other reducing agents are sometimes substituted for the ferrous sul- 
phate. Even decaying vegetable matter effects the conversion of blue 
into white indigo in an alkaline liquid. Thus, for some purposes, the vat 
is prepared by fermenting a mixture of indigo, madder, carbonate of 
potash, and lime, when the hydrogen extricated in the fermentation of the 
vegetable matter converts the blue into white indigo, which is then dis- 
solved by the potash liberated from the carbonate by the lime, f 

"When cloth is dyed with indigo (Saxony blue) the colour is dissolved 

* This formula, which is double that formerly employed, agrees with the vapour-density 
of indigo, which has been found to be 9*45 (air=l). 

f Sodium hydrosulphite may be employed for the reduction of indigo. To prepare it, 
solution of bisulphite of soda is placed in contact with zinc for an hour in a closed vessel. 
The solution is mixed with the indigo and milk of lime (see p. 214). 



608 DYEING AND CALICO-PEINTING. 

by means of sulphuric acid. Fuming sulphuric acid dissolves indigo blue 
very readily, but oil of vitriol does not act quite so well. The solution 
thus obtained is commonly called sulphindlgotic acid, but it really contains 
two acids, the sidphindylic (HC 8 H 4 NO.S0 3 ) and hyposidpliindigotic. The 
blue solution becomes colourless when shaken with powdered zinc, and 
resumes its blue colour when shaken with air. 

On heating indigo, it evolves purple vapours, which condense in pris- 
matic crystals of a coppery lustre, consisting of pure indigotine or indigo 
blue, which may be obtained in larger quantity by digesting indigo with 
grape-sugar, caustic soda, and weak alcohol, when a solution of white 
indigo is obtained which deposits the crystallised indigotine on exposure 
to air. 

Artificial Indigo. — This colouring matter has been obtained from the toluene of 
coal-tar, but the process is at present too expensive to be commercially successful. 
The steps of the conversion are the following :— 

(1) C 6 H,.CH 3 (toluene)- + C1 4 = 2HC1 + C 6 H 5 .CHC1 2 (benzylene dichloride) ; (2) C 6 H 5 . 
CHC1 2 + 2KHO = 2KC1 + H,0 +C 6 H 5 .CHO (benzaldehyde) ; (3) C 6 H 5 .CHO + CH 3 . 
COC1 {acetijle chloride) = C 6 H 5 .C 2 H o .C0 2 H (cinnamic acid) + HC1; (4) C 6 H 5 .C 2 H 2 . 
C0 2 Hj+ HN0 3 = C 6 H 4 N0 2 .C 2 H 2 .C6. 2 H {nitrocinnamic acid) + H 2 ; (5) C 6 H 4 N0 2 . 
CoH9.C0 2 H + Br 2 = CfiH 4 N0 2 .C 2 H 2 Bi\>.C0 H (dibromnitrophenyl propionic acid); 
( (?) C 6 H 4 N0 2 . C 2 H 2 Br 2 . C0 2 H + 2NaOH = C 6 H 4 N0 2 . C 2 C0 2 H (nitrophenyl propiolic acid) 
+ 2NaBr + 2H 2 0; (7) By heating this last acid with a reducing agent, such as an 
alkaline solution of grape-sugar, the latter is made to appropriate the oxygen of two 
molecules of water, the hydrogen of which acts upon the acid, converting it into in- 
digo blue; 2C 9 H 5 N0 4 (nitrophenyl propiolic acid) + 2H 2 = 2CO 2 + 2H 2 O + C 16 H 10 N 2 O 2 
(indigo). 

429. Animal colouring matters. — From the animal kingdom only two 
colouring matters of any great importance are derived, viz., cochineal and 
lac, both which are obtained from insects of the coccus tribe. The colour- 
ing matter of cochineal is known as carmine, and may be extracted from 
the insects by water or alcohol. It has acid properties, and has been 
named carminic acid (C 1 yH 18 O 10 ). Carmine-lake is a combination of this 
acid with alumina, precipitated when a solution of alum and an alkaline 
carbonate are added to one of cochineal. 

Dyeing and Calico-Printinc. 

430. The object of the dyer being to fix certain colouring matters 
permanently in the fabric, his processes would be expected to vary with 
the nature of the latter and of the colour to be applied to it. In order 
that uniformity of colour and its perfect penetration into the fibre may be 
attained, it is evident that the colouring matter must always be employed 
in a state of solution; and it must be rendered fast,, or not removable by 
washing, by assuming an insoluble condition in the fibre. 

The simplest form of dyeing is that in which the fibre itself forms an 
insoluble compound with the colouring matter. Thus, if a skein of silk 
be immersed in a solution of indigo in sulphuric acid, it removes the whole 
of the colouring matter from the liquid, and may then be washed with 
water without losing colour ; but if the same experiment be tried with 
cotton, the indigo will not be withdrawn from the solution, and when the 
cotton has been well squeezed and rinsed with water, it will become white 
again. It may be stated generally, that the animal fabrics (silk and wool) 
will absorb and retain colouring matters with much greater facility than 
vegetable fabrics (cotton and linen). In the absence of so powerful an 



DYEING AND CALICO-PRINTING. 609 

attraction between the fibre and the colouring matter, it is usual to impreg- 
nate the fabric with a mordant or substance having an attraction for the 
colour, and capable of forming an insoluble combination with it, so as to 
retain it permanently attached to the fabric. Thus, if a piece of cotton 
be boiled in a solution of acetate of alumina, the alumina will be precipi- 
tated in the fibre ; and if the cotton be then soaked in solution of 
cochineal or of logwood, the red colouring matter will form an insoluble 
compound (or lake) with the alumina, and the cotton will be dyed of a 
fast red colour. 

Another method of fixing the colour in the fabric consists in impregnat- 
ing the latter with two or more liquids in succession, by the admixture of 
which the colour may be produced in an insoluble state. If a piece of 
any stuff be soaked in solution of ferric chloride, and afterwards in 
potassium ferrocyanide, the Prussian blue which is precipitated in the 
fibre will impart a fast blue tint. 

An indispensable preliminary step to the dyeing of any fabric is the 
removal of all natural grease or colouring matter, which is effected by 
processes varying with the nature of the fibre, and is preceded, in the 
cases of cotton and woollen materials which are to receive a pattern, by 
certain operations of shaving and singeing for removing the short hairs 
from the surface. 

From linen and cotton, the extraneous matters (such as grease and resin) 
are generally removed by weak solutions of carbonate of potassium or of 
sodium, and the fabrics are afterwards bleached by treatment with chloride 
of lime (page 155). But since the fibres of silk and wool are much more 
easily injured by alkalies and by chlorine, greater care is requisite in 
cleansing them. Silk is boiled with a solution of white soap to remove 
the gum, as it is technically termed ; but the natural grease is extracted 
from wool by soaking at a moderate temperature in a weak bath either of 
soap or of ammoniacal (putrefied) urine. Both silk and wool are bleached 
by sulphurous acid (page 200). 

Among the red dyes the most important are madder, alizarine, Brazil 
wood, cochineal, lac, and the colours derived from aniline. 

In dyeing red with madder or Brazil wood, the linen, cotton, or wool 
is first mordanted by boiling in a solution containing alum and bitartrate 
of potash, when it combines with a part of the alumina, and on plunging 
the stuff into a hot infusion of madder, the colouring matter forms an 
insoluble combination with that earth. 

To dye Turkey-red, the stuff is also mordanted with alum, but has pre- 
viously to undergo several processes of treatment with oil and with galls, 
the necessity of which is satisfactorily established in practice, though it 
is not easy to explain their action. The colour is finally brightened by 
boiling the stuff with chloride of tin. 

Woollen cloth is dyed scarlet with lac or cochineal, having been first 
mordanted by boiling in a mixture of perchloride of tin and bitartrate of 
potash. 

The aniline colours (see page 460) are employed for dyeing silk and 
wool, either without any mordant or with the help of albumen. 

Blues are generally dyed with indigo (p. 607), or with Prussian blue; 
in the latter case the stuff is steeped successively in solutions of a salt of 
peroxide of iron and of potassium ferrocyanide. Aniline blue is also 
much employed for silk and woollen fabrics. 

2 Q 



610 PATTERNS IN CALICO-PRINTING. 

The principal yellow dyes are weld, quercitron, fustic, annatto, chrys- 
aniline, and lead chromate. For the four first colouring matters aluminous 
mordants are generally applied. Lead chromate is produced in the fibre 
of the stuff, which is soaked for that purpose, first in a solution of acetate 
or nitrate of lead, and then in potassium chromate, Carbazotic or picric 
acid (page 465) is also sometimes employed as a yellow dye. 

In dyeing blacks and browns, the stuffs are steeped first in a bath con- 
taining some form of tannin (page 592), such as infusion of galls, sumach, 
or catechu, and afterwards in a solution of a salt of iron, different shades 
being produced by the addition of indigo, of copper sulphate, &c. 

431. The art of calico-printing differs from that of dyeing, in that the 
colour is required to be applied only to certain parts of the fabric so as to 
produce a pattern or design either of one or of several colours. 

A common method of printing a coloured pattern upon a white ground 
consists in impressing the pattern by passing the stuff under a roller, to 
which an appropriate mordant thickened with British gum (page 492) is 
applied. The stuff is then dunged, i.e., drawn through a mixture of cow- 
dung and water, which appears to act by removing the excess of the 
mordant, and afterwards immersed in the hot dye-bath, when the colour 
becomes permanently fixed to the mordanted device, but may be removed 
from the rest of the stuff by washing. 

If the pattern be printed with a solution of acetate of iron, and the stuff 
immersed in a madder-bath, a lilac or black pattern will be obtained 
according to the strength of the mordant employed. By using acetate of 
alumina as a mordant, the madder-bath would give a red pattern. 

A process which is the reverse of this is sometimes employed, the 
pattern being impressed with a resist, that is, a substance which will pre- 
vent the stuff from taking the colour in those parts which have been 
impregnated with it. For example, if a pattern be printed with thickened 
tartaric or citric acid, and the stuff be then passed through an aluminous 
mordant, the pattern will refuse to take up the alumina, and subsequently 
the colour from the dye-bath. Or a pattern may be printed with nitrate 
of copper, and the stuff passed through a bath of reduced indigo (page 607), 
when the nitrate of copper will oxidise the indigo, and by converting it 
into the blue insoluble form, will prevent it from sinking into the fibre of 
those parts to which the nitrate has been applied, whilst elsewhere, the 
fibre, having become impregnated with the white indigo, acquires a fast 
blue tint when exposed to the air. 

Sometimes the stuff is uniformly dyed, and the colour discharged in 
order to form the pattern. A white pattern is produced upon a red 
(madder) or blue (indigo) ground by printing with a thickened acid dis- 
charge, and passing the stuff through a weak bath of chloride of lime, 
which removes the colour from those parts only which were impregnated 
with the acid (page 156). By adding lead nitrate to the acid discharge, 
and finally passing the stuff through solution of potassium chromate, a 
yellow pattern (lead chromate) may be obtained upon the madder red 
ground. By applying nitric acid as a discharge, a yellow pattern may be 
obtained upon an indigo' ground (page 136). 

Very brilliant designs are produced by mordanting the stuff in a solu- 
tion of stannate of potassium or sodium (page 348), and immersing it in 
dilute sulphuric acid, which precipitates the stannic acid in the fibre. 



DIFFICULTIES OF ANIMAL CHEMISTRY. 611 

When the thickened colouring matters' are printed on in patterns, and 
exposed to the action of steam, -an insoluble compound is formed between 
the colour and the stannic acid, which usually exhibits a very fine and 
permanent colour. 

It is evident that by combining the principles of which an outline has 
just been given, the most varied parti-coloured patterns may be printed. 

ANIMAL CHEMISTRY. 

432. Our acquaintance with the chemistry of the substances composing 
the bodies of animals is still very limited, although the attention of many 
accomplished investigators has been directed to this branch of the science. 
The reasons for this are to be found, firstly, in the susceptibility to change 
exhibited by animal substances, when removed from the influence of life ; 
and secondly, in the absence, in such substances, of certain physical pro- 
perties by which we might be enabled to separate them from other bodies 
with which they are associated, and to verify their purity when obtained 
in a separate state. Two of the most important of these properties are 
volatility and the tendency to crystallise. When a substance can suffer 
distillation without change, it will, be remembered that its boiling-point 
affords a criterion of its purity ; or if it be capable of crystallising, this 
may be taken advantage of in separating it from other substances which 
crystallise more or less easily than itself, and its purity may be ascertained 
from the absence of crystals of any other form than that belonging to the 
substance. But the greater number of the components of animal frames 
can neither be crystallised nor distilled, so that many of the analyses which 
have been made of such substances differ widely from each other, because 
the analyst could never be sure of the perfect purity of his material ; and 
even when concordant results have been obtained as to the percentage com- 
position of the substance, the atomic formula deduced from it has been of 
so singular and exceptional a character as to cast very strong suspicion 
upon the purity of the substance. 

Accordingly, the chemical formulae of a great many animal substances 
are perfectly unintelligible, conveying not the least information as to the 
position in which the compound stands with respect to other substances, 
or the changes which it might undergo under given circumstances. 

It has been shown in the previous chapters of this work that we are 
gradually learning to class all compound bodies under a few typical forms, 
so that the chemical properties of any substance may in many cases be 
predicted from its composition as indicating the type to which it belongs. 
Take, for example, the class of alcohols C n H 2n+2 0), or of volatile acids 
(C„H 2n 2 ), or of ammonias (XY 3 ), and it will be seen that even those 
formulas which are apparently the most complex are perfectly intelligible 
when referred to their proper type (page 545). But the extraordinary 
formulae, for example, deduced from the ultimate analysis of albumen, 
Cr-2^-112-^18^^22' anc ^ caseine, C 144 H 228 N 36 45 S, cannot be referred to any 
known type, and refuse to be classed with other substances, even if a 
type were invented expressly for them. 

Animal chemistry is for the above reasons in a very backward condition, 
as compared with vegetable and mineral chemistry, though an observation 
of the progress of research affords us the consolation, that a steady advance 
is being made towards a generalisation of the facts which have been dis- 



612 MILK. 

covered, especially by analogical reasoning from those two other depart- 
ments of the science. 

Milk. — The chemistry of milk is well adapted to introduce the study of 
animal chemistry, because that liquid contains representatives of all the 
substances which make up the animal frame ; and it is on this account that 
it occupies so high a position among articles of food. 

Although, to the unaided eye, milk appears to be a perfectly homo- 
geneous fluid, the microscope reveals the presence of innumerable globules 
floating in a transparent liquid, which is thus rendered opaque. If milk 
be very violently agitated for several hours, masses of an oily fat (butter, 
p. 584) are separated from it, and leave the liquid transparent. This fat 
was originally distributed throughout the milk, in minute globules enclosed 
in very thin membranes which were torn by the violent agitation, and the 
fatty globules then cohered into larger masses. 

For the preparation of butter, it is usual to allow the milk to stand for 
some hours, when a layer of cream collects upon the surface, the proportion 
of which is very variable, but is generally about y^th of the volume of the 
milk. The skimmed milk retains about half of the fatty matter. This 
cream contains about 5 per cent, (by weight) of fat, 3 per cent, of caseine, 
and water. When the cream is churned, the enclosing membranes of the 
fat globules are broken, and the fat unites into a semi-solid mass of butter, 
from which the butter-milk containing the caseine may be separated. If 
this be not done effectually, the caseine which is left in the butter, being a 
nitrogenised substance, will soon begin to decompose, and will induce a 
decomposition in the butter (page 584), resulting in the formation of 
certain volatile acids, which impart to it a rancid and offensive taste and 
odour. To prevent this, salt is generally added to butter which has been 
less carefully prepared, in order to preserve the caseine from decomposition. 
Butter-milk contains about one-fourth of the fatty matter of the milk. 

Pure butter is essentially a mixture of margarine and oleine with smaller 
quantities of other fats, such as butyrine, caprine, and caproine (page 584). 

Fresh milk is slightly alkaline to test-papers, but after a short time it 
acquires an acid reaction; and if it be then heated, it coagulates from the 
separation of the caseine. This spontaneous acidification of milk is caused 
by the fermentation of the sugar of milk, which results in the produc- 
tion of lactic acid, according to the equation, C 12 H 24 12 [Sugar of milk) 
= 4HC 3 II 5 03 (Lactic acid)- 

The caseine, being insoluble in the acid fluid, separates in the form of 
curd. This development of lactic acid is spoken of as the lactic fermenta- 
tion, and may be excited not only in milk-sugar, but in other substances 
analogous to it. This is taken advantage of in the preparation of lactic 
acid, for which purpose 8 parts of cane-sugar are dissolved in 50 parts of 
water, and 1 part of poor cheese with 3 parts of chalk are added to the 
mixture, which is then allowed to remain for some weeks at about 80° F. 
The lactic acid formed from the cane-sugar (C 12 H 22 11 ) under the 
influence of the changing caseine in the cheese, decomposes the chalk, 
forming crystals of calcium lactate, Ca^H^O^. This is dissolved in 
boiling water, recrystallised in order to purify it, and digested with one- 
third of its weight of sulphuric acid, which converts the lime into sulphate, 
liberating the lactic acid; by adding alcohol, the whole of the sulphate 
of lime is precipitated, and the lactic acid is dissolved by the alcohol, 
which leaves it on evaporation as a colourless, syrupy, very acid liquid, 



LACTIC ACID— CHEESE. 613 

which may be distilled, though with some loss from decomposition, if 
heated out of contact with air. 

By heating lactic acid to about 270° F. for a considerable length of time, 
a molecule of water is expelled, and the lactic anhydride (C 6 H 10 O 5 ) is left 
as a brownish glassy substance, which is reconverted into the acid by 
boiling with water. At a temperature of 500° F. lactic acid undergoes a 
destructive distillation, the most interesting product of which is a trans- 
parent crystalline substance called lactide (C 3 H 4 2 ), differing from lactic 
acid by the elements of water, which it resumes when dissolved in that 
liquid, being converted into lactic acid (C 3 H 6 3 ). When lactic acid is 
heated with hydriodic acid in a sealed tube, it is converted into propionic 
acid; HC 3 H 5 3 {Lactic acid) + 2HI = HC 3 H 5 2 (Propionic acid) + H 2 + I 2 . 

When lactic acid is heated in contact with diluted sulphuric acid it 
yields aldehyde and formic acid. 

Lactic acid is an important constituent of the animal body, being found 
in the juice of muscular flesh, in the gastric juice, &c. 

If milk be maintained at a temperature of about 90° F., the fermentation 
results in the production of alcohol and carbonic acid, for although milk- 
sugar is not fermented like ordinary sugar by contact with yeast, it appears, 
under the influence of the changing caseine at a favourable temperature, 
to be converted first into grape-sugar (page 496), and afterwards into 
alcohol and carbonic acid. The Tartars prepare an intoxicating liquid 
which they call koumiss, by the fermentation of milk, 

When an acid is added to milk, the caseine is separated in the form of 
curd, in consequence of the neutralisation of the soda which retains it 
dissolved in fresh milk, and this curd carries with it, mechanically, the 
fat globules of the milk, leaving a clear yellow whey. 

In the preparation of cheese, the milk is coagulated by means of rennet, 
which is prepared from the lining membrane of a calf's stomach. This is 
left in contact with the warm milk for some hours, until the coagulation 
is completed. This action of rennet upon milk depends upon the presence 
of certain microscopic organisms. The curd is collected and pressed into 
cheeses, which are allowed to ripen in a cool place, where they are 
occasionally sprinked with salt. The peculiar flavour which the cheese 
thus acquires is due to the decomposition of the caseine, giving rise to the 
production of certain volatile acids, such as butyric, valerianic, and 
caproic, which have very powerful and characteristic odours. If this 
ripening be allowed to proceed very far, ammonia is developed by the 
putrefaction of the caseine, and in some cases the ethers of the above- 
mentioned acids are produced, at the expense probably of a little sugar of 
milk left in the cheese, conferring the peculiar aroma perceptible in some 
varieties of it. 

The different kinds of cheese are dependent upon the kind of milk used 
in their preparation, the richer cheeses being, of course, obtained from 
milk containing a large proportion of cream; such cheese fuses at a 
moderate heat, and makes good toasted cheese, whilst that which contains 
little butter never fuses completely, but dries and shrivels like leather. 
Double Gloucester and Stilton are made from a mixture of new milk and 
cream; Chedder cheese is made from new milk alone. Cheshire and 
American cheeses, from milk robbed of about one-eighth of its cream. 
Dutch cheese and the Skim Dick of the midland counties, from skimmed 
milk. 



614 CASEINE — SUGAR OF MILK. 

Caseine. — The pure curd of milk is known as caseine, and consists 
essentially of carbon, hydrogen, nitrogen, oxygen, and a small proportion 
(one per cent.) of sulphur. The simplest expression of the result of the 
analysis of caseine would be C 144 H 228 N 36 45 S, but the anomalous com- 
plexity of this formula conveys a suspicion that the composition of pure 
caseine has yet to be fixed. By whatever process it has been purified, 
hitherto it has always been found to retain saline matters. The com- 
plexity of its composition accounts for its liability to undergo putrefactive 
decomposition. 

Coagulated caseine is characterised by the facility with which it is dis- 
solved by alkaline solutions, such as Sodium carbonate, yielding a liquid 
upon the surface of which, when boiled, an insoluble pellicle forms, exactly 
similar to that which forms upon the surface of boiled milk. Coagulated 
caseine may also be dissolved by acetic or oxalic acid, but the addition of 
sulphuric or hydrochloric acid reprecipitates it, these acids apparently 
forming insoluble compounds with caseine. 

If skimmed milk be carefully evaporated to dryness and the fat extracted 
from the residue by ether, the caseine is left in the soluble form mixed 
with milk-sugar, and is capable of dissolving in water or in weak alcohol. 

Caseine appears to possess the properties of a weak acid, since it com- 
bines both with the alkalies and alkaline earths, and is even said to be 
capable of partially neutralising the former. A mixture of cheese and 
slaked lime is sometimes used as a cement for earthenware, the caseine 
combining with the lime to form a hard insoluble mass. The curd of 
milk, washed and dried, is used by calico-printers, under the name of 
lactarine, for fixing colours. If it be dissolved in weak ammonia, mixed 
with one of the aniline dyes, printed on calico, and steamed, the ammonia 
is expelled, and the colour is left behind as an insoluble compound with 
the caseine. 

Caseine, or a substance so closely resembling it as to be easily con- 
founded with it, is found in peas, beans, and most leguminous seeds. If 
dried peas be crushed and digested for some time in tepid water, a turbid 
liquid is obtained, holding starch in suspension. If this be allowed to 
settle, the clear liquid is an impure aqueous solution of legumine, or vege- 
table caseine, which constitutes about one-fourth of the weight of the 
peas. 

This solution is not coagulated by heat, but becomes covered with a 
pellicle similar to that which forms upon the surface of boiled milk. It 
is coagulated by acetic acid and by rennet, just as is the case with the 
caseine of milk. 

Sugar of milk. — When whey is evaporated to a small bulk and allowed 
to cool, it deposits hard white prismatic crystals of sugar of milk, or lactine 
(C 12 H 24 12 ), which is much less soluble, and therefore less sweet than 
cane-sugar. Like this, it is converted into glucose (C 6 H 12 6 ), when boiled 
with dilute acids. Milk-sugar resembles the other sugars in its capability 
of combining with some bases, stich as the alkalies, alkaline earths, and 
oxide of lead ; with the latter it forms two insoluble compounds. 

At about 280° F. the crystals of milk-sugar lose a molecule of water 
and become C 12 H 22 O n . ' At 400° F. the sugar fuses, and 2 molecules 
lose 5 molecules of water. 

It will be seen that the characteristic constituents of milk are the caseine 
and milk-sugar, but the proportions in which these are present vary widely, 



CONSTITUTION OF BLOOD, 615 

not only with the animal from which the milk is obtained, but with 'the 
food and condition of the animal. A general notion of their relative 
quantities, however, may be gathered from the following table, exhibiting 
the results of the analyses made by Boussingault : — 





Cow. 


Ass. 


Goat. 


Woman. 


Water, 




87-4 


90-5 


82-0 


88-4 


Butter, 




4-0 


1'4 


4-5 


2'5 


Milk-sugar r 
Soluble salts, 


■! 


5-0 


6-4 


4-5 


4-8 


Caseine, 
Insoluble salts, 


•1 


3-6 


1-7 


9-0 


3-8 



The soluble salts present in milk include the phosphates and chlorides 
of potassium and sodium, whilst the insoluble salts are the phosphates of 
calcium, magnesium, and iron. All these salts are in great request for 
the nourishment of the animal frame. 

The milk supplied to consumers living in towns is subject to consider- 
able adulteration ; but in most cases this is effected by simply removing 
the cream and diluting the skimmed milk with water, a fraud which is 
not easily detected, as might be supposed, by determining the specific 
gravity of the milk, for since milk is heavier tban water (1*032 sp. gr.), 
and the fatty matter composing cream is lighter than water, a certain 
quantity of cream might be removed, and water added, without altering 
the specific gravity of the milk. 

The simplest method of ascertaining the quality of the milk consists 
in setting it aside for twenty-four hours in a tall narrow tube (lactometer), 
divided into 100 equal parts, and measuring the proportion of cream which 
separates, this averaging, in pure milk, from eleven to thirteen divisions. 
By shaking milk with a little potash (to dissolve the membrane which 
envelops the fat globules) and ether, the butter may be dissolved in the 
ether which rises to the surface, and if this be poured off and allowed to 
evaporate, the weight of the butter may be ascertained; or the milk may 
be evaporated by a steam heat, and the fat dissolved by treating the 
residue with ether. One thousand grains of milk should give, at least, 
27 or 28 grains of butter. Since, however, the milk of the same cow gives 
very different quantities of cream at different times, it is difficult to state 
confidently that adulteration has been practised. The standard usually 
adopted by analysts is 25 grains of fat or butter and 90 grains of " solids 
not fat " in 1000 grains of milk. 



o a 



433. Blood. — The blood from which the various organs of the body 
directly receive their nourishment is the most important, as well as the 
most complex of the animal fluids. Its chemical examination is attended 
with much difficulty, on account of the rapidity with which it changes 
after removal from the body of the animal. 

On examining freshly-drawn blood under the microscope, it is observed 
to present some resemblance to milk in its physical constitution, consisting 
of opaque flattened globules floating in a transparent liquid ; the globules, 
in the case of blood, having a well-marked red colour. 

In a few minutes after the blood has been drawn, it begins to assume a 
gelatinous appearance, and the semi-solid mass thus formed separates into 
a red solid portion or clot; which continues to shrink for ten or twelve 



616 COMPOSITION OF BLOOD GLOBULES. 

hours, and a clear yellow liquid or serum. It might be supposed that this 
coagulation is due to the cooling of the blood, but it is found by experi- 
ment to take place even more rapidly when the temperature of the blood 
is raised one or two deg rees after it has been drawn • and on the other 
hand, if it be artificially cooled, its coagulation is retarded. Indeed, the 
reason for this remarka Me behaviour of the blood is not yet understood. 

If the coagulum or clot of blood be cut into slices, tied in a cloth, and 
well washed in a stream of water, the latter runs off with a bright red 
colour, and a tough yellow filamentous substance is left upon the cloth ; 
this substance is called fibrine, and its presence is the proximate cause of 
the coagulation of the blood, for if the fresh blood be well whipped with 
a bundle of twigs or glass rods, the fibrine will adhere to them in yellow 
strings, and the defibrinated blood will no longer coagulate on standing. 
If this blood, from which the fibrine has been extracted, be mixed with 
a large quantity of a saline solution (for example, 8 times its bulk of a 
saturated solution of sodium sulphate), and allowed to stand, the red 
globules subside to the bottom of the vessel. 

These globules are minute bags of red fluid, enclosed in a very thin 
membrane or cell-wall, and if water were mixed with the defibrinated 
blood, since its specific gravity is lower than that of the fluid in the 
globules, it would pass through the membrane (by endosmose), and so 
swell the latter as to break it and disperse the contents through the liquid. 

The red fluid contained in these blood globules consists of an aqueous 
solution, containing as its principal constituents a substance known as 
globidine y which very nearly resembles albumen, and the peculiar colouring 
matter of the blood, which is called hcematine. 

Beside these, the globules contain a little fatty matter and certain 
mineral constituents, especially the iron (which is associated in some 
unknown form with the colouring matter), the chlorides of sodium and 
potassium, and the phosphates of potassium, sodium, calcium, and 
magnesium. 

Though the quantities of these constituents are not invariable, even in 
the same individual, the following numbers may be taken as representing 
the average composition of these globules : — • 

1000 parts of Blood Globidcs contain — 

Organic substances of ) 
unknown nature, \ 



Water, . . . • . 688*00 

Globuline, . . . 282*22 

Hsematine, . . . 16*75 

Fat, .... 2*31 



. 2*60 
Mineral substances,* . .8*12 



Potassium, . . . 3*328 

Phosphoric oxide (P o 6 ), . 1*134 

Sodium, . " . ■ . . 1*052 

Chlorine, . . . 1*686 



The mineral substances consist of— 

Oxygen, 0*667 

Calcium phosphate, . . 0*114 

Magnesium phosphate, . 0*073 

Sulphuric oxide (S0 3 ), . 0*066 

Globuline is a substance very similar in its character and composition 
to albumen; it is found also in large proportion in the matter composing 
the crystalline lens of the eye. 

Nucleine is another albuminoid body found in the blood globules of 
snakes and birds; it is remarkable for its insolubility in water, alcohol, 
ether, and dilute acids or alkalies. It appears to be the chief component 
of the cell-nucleus or cytoblast. 

* Exclusive of the iron which is associated with the hsematine. 



■«■■ 



COMPOSITION OF BLOOD GLOBULES. 617 

The hcematine or hcematosine must be accounted the most important 
constituent of the blood globules, since it appears to be more intimately 
connected than any other with the functions discharged by the blood in 
nutrition and respiration. 

In order to obtain it in the separate state, the blood globules are boiled 
with alcohol acidulated with sulphuric acid, and the red solution mixed 
with ammonium carbonate, which separates the greater part of the globu- 
line ; the filtered liquid is evaporated to dryness, and all soluble matters 
are extracted by successive treatments with water, alcohol, and ether. By 
again dissolving the brown residue in alcohol containing ammonia, filter- 
ing, evaporating to dryness, and removing any soluble matter by water, a 
dark brown substance is obtained, which is supposed to be pure hsematine, 
though no longer in the soluble state in which it existed in the blood. It 
is now dissolved only by alkalies or by acidulated alcohol. 

In its chemical composition hsematine is remarkable for the presence of 
iron, associated in a very intimate manner with carbon, hydrogen, nitrogen, 
and oxygen, so that it cannot be recognised by the ordinary tests. The 
formula which has been assigned to it is C 34 H 36 N 4 5 Fe, but it is very 
doubtful whether it has been analysed in a perfectly pure state. 

The most important chemical property of hsematine is its behaviour with 
oxygen. It is well known that the blood issuing from an artery has a much 
brighter red colour than that drawn from a vein, and that when the latter 
is allowed to coagulate, the upper part of the clot, which is in contact with 
the air, is brighter than the lower part. 

When the dark red blood drawn from a vein is shaken up with air or 
oxygen, a quantity of the latter is absorbed, and a nearly equal volume of 
carbonic acid gas is disengaged, the dark red colour being at the same 
time changed to the bright red characteristic of arterial blood. The 
carbonic acid gas exists already formed in the venous blood, and is given 
off if the blood is exposed under an exhausted receiver. The condition 
assumed by the oxygen when absorbed by the blood is not yet clearly 
understood, but it is generally allowed that the conversion of venous into 
arterial blood is due to the displacement of carbonic acid gas by oxygen. 

Recent experiments indicate that haematine is really a product of the 
alteration of another body existing in the blood globules, which has been 
named hcemaglobine. This substance is obtained by treating the blood- 
globules with water, adding alcohol, and cooling in a mixture of ice and 
salt, when the hsemaglobine crystallises out in shapes differing in different 
animals. By treating hsernaglobine with common salt and glacial acetic 
acid, the so-called blood-crystals are obtained, which appear to be composed 
of hsematine and hydrochloric acid. 

Hsemaglobine contains carbon 54*2 per cent., hydrogen 7 "2, nitrogen 
16, oxygen 21*5, 'sulphur 0*7, iron 0*4. Its solution absorbs oxygen, 
acquiring a bright red colour, and if daylight be transmitted through this 
solution, and afterwards through the prism of a spectroscope (p. 272), the 
green portion of the spectrum is seen to be crossed by two broad black 
bands, which are also seen when arterial blood is employed. When 
venous blood is examined in the same way, it exhibits only one broad 
black band, not coincident with either of those furnished by arterial 
blood; but on shaking the venous blood with air till it has become red, 
the two black absorption bands are seen in its spectrum. Arterial blood 
which has been shaken with carbonic acid gas gives the single broad band 



618 COMPOSITION OF LIQUOR SANGUINIS. 

characteristic of venous blood. These optical properties are found useful 
for the identification of blood-stains. 

The liquid in which the blood globules float is an alkaline solution con- 
taining albumen, fibrine, and saline matters in about the proportions here 
indicated. 





1000 parts of Liquor Sanguinis contain — 




"Water, 


902*90 Organic substances of un- ) 


3-94 


Albumen, 


. 78-84 


known nature, . \ 


Fibrine, . 


4-05 


Mineral substances, . 


8-55 


Fat, 


172 








The mineral substances consist of— 




Sodium, . 


. 3-341 


Phosphoric oxide (P 2 5 ), 


0-191 


Chlorine, . 


. 3-644 


Sulphuric oxide (S0 3 ), 


0-115 


Potassium, 


. 0-323 


Calcium phosphate, . 


0-311 


Oxygen, . 


. 0-403 


Magnesium phosphate, 


0-222 



The alkaline character of this liquid appears to be due to the presence 
of carbonate and phosphate of sodium. 

The albumen present in the serum of blood causes it to coagulate to a 
gelatinous mass when heated, this property being the distinctive feature 
of albumen. This substance may be obtained as a transparent yellow 
mass, resembling gum, and dissolving slowly in water, by evaporating 
either serum of blood or white of egg below 120° F. ; but if the tempera- 
ture be raised above that point, the albumen is coagulated, and cannot be 
redissolved in water unless heated with it under pressure. 

Albumen, like caseine, has never been obtained perfectly free from 
saline matters, particularly the alkaline and earthy phosphates, and much 
difficulty attends the exact determination of its composition. The 
analysis, by G. S. Johnson, of some remarkable compounds of albumen 
with the acids, confirms the formula originally proposed by Lieberkuhn, 
viz., C 72 H 112 ]N" 18 S0 22 {Journal of the Chemical Society, August 1874). 

It will be remembered that a substance identical with, or very closely 
resembling albumen, and known as vegetable albumen, is found in those 
vegetable juices which are coagulated by heat. 

Fibrine, as existing in blood, differs from all other animal substances 
by its tendency to spontaneous coagulation. When coagulated it exhibits 
characters very similar to those of coagulated albumen ; but when sepa- 
rated from the freshly-drawn blood by violent stirring, it forms elastic 
strings which dry into a yellow horny mass. Fibrine is one of the most 
important constituents of the animal frame, for all muscular flesh consists 
of this substance. The gluten found in the seeds of the cerealia bears a 
very close resemblance to fibrine, and is often called vegetable fibrine. 

The same formula has been often assigned to fibrine as to albumen, and 
its complexity would explain its disposition to putrefy when removed 
from the influence of life. It does not appear quite certain that the 
fibrine dissolved in the blood is identical in composition with that of 
muscular fibre. Some analyses have shown that the muscular fibrine 
contains more oxygen than blood-fibrine, and this latter more than albumen, 
affording some ground for the belief that the blood-fibrine represents the 
transition state between the albumen of the serum and the muscular flesh 
into which it is eventually converted. 

Albumen, fibrine, and caseine have been regarded by some chemists 
as compounds of the same primary substance (proteine) combined with 



EGGS — JUICE OF FLESH. 619 

different proportions of sulphur and phosphorus, the proteine being 
isolated by boiling the albuminous body with potash and precipitating the 
solution by an acid. The composition usually assigned to this substance 
is C 18 H 27 ]S" 4 6 ; but since it is neither crystallisable nor capable of conver- 
sion into vapour, there is no proof of its purity ; and the great use which 
has been made of this substance by writers on animal chemistry is dua to 
the apparent simplicity which it confers upon the relations existing 
between the numerous modifications of albumen, fibrine, and caseine, tho- 
ultimate formulae of which present so high a degree of complexity. 

In the substance of the brain there has been found a very remarkable 
crystalline substance, which has been termed protagon, and is a complex 
compound of carbon, hydrogen, nitrogen, oxygen, and perhaps phosphorus, 
to which no probable formula has yet been assigned. It is very easily 
decomposed, even below 212°. Protagon is insoluble in water, but dis- 
solves in hot alcohol and in acetic acid. When boiled with solution of 
baryta, it yields phosphoglyceric acid, and a strongly alkaline base, murine. 

Eggs. — The shell of the egg contains about nine-tenths of its weight 
of calcium carbonate, associated with animal matter. The white of egg 
consists of albumen (about 12 per cent.), water (about 86 per cent.), and 
small quantities of soluble salts. It is alkaline, from the presence of a 
little soda. Raw white of egg has no smell of sulphuretted hydrogen, 
and does not blacken silver ; but after boiling, both these properties are 
manifested, showing that it suffers some decomposition during coagula- 
tion. 

Yolk of egg contains a modification of albumen termed vitelline, and 
owes its colour to a yellow oil which may be extracted with ether, and 
contains phosphoric acid. The yolk of hens' eggs has about half the 
weight of the white, and commonly contains about half its weight of 
water, 1 6 per cent, of vitelline, 30 per cent, of fat, and 1 '5 per cent, of 
saline matters. 

434. Elesh.— The fibrine composing muscular flesh contains about 
three-fourths of its weight of water, a part of which is due to the blood 
contained, in the vessels traversing it, and another part to the juice of flesh, 
which may be squeezed out of the chopped flesh. In this juice of flesh 
there are certain substances which appear to play a very important part 
in nutrition. The liquid is distinctly acid, which is remarkable when 
the alkaline character of the blood is considered, and contains phosphoric, 
lactic, and butyric acid, together with kreatine, inosite, and saline matters. 
By soaking minced flesh in cold water and well squeezing it in a cloth, 
a red fluid is obtained containing the juice of flesh mixed with a little 
blood. When the liquid is gently heated, the albumen of the blood and 
of the juice is coagulated in flakes stained with the colouring matter ; 
the liquid filtered from these may be mixed with baryta water to precipi- 
tate the phosphoric acid ; and after a second filtration, evaporated to a 
syrupy consistence and set aside, when beautiful colourless prismatic 
crystals are obtained, consisting of a feeble organic base called kreatine* 
the composition of which is represented by the formula C 4 H 9 N 3 2 Aq. 

The quantity of this substance obtained from the flesh of different 
animals varies very considerably, that of fowls having been found hitherto 
most productive, and next, that of fish. One thousand parts of the flesh 

* From /cpe'as, flesh. 



f)20 COOKING OF MEAT. 

of fowl furnished 3-2 parts of kreatine, 1000 parts of cod, 1-71 of kreatine, 
and 1000 of beef, 0*70 parts. Human flesh is said to contain a large pro- 
portion of kreatine. 

When boiled with acids, kreatine loses the elements of water, and is 
converted into a powerful base called kreatinine (C 4 H 7 N 3 0), which is also 
found in minute proportion, accompanied by kreatine, in the urine. 

Boiled with alkalies, kreatine gains the elements of water, and furnishes 
two organic bases, urea (also found in urine), and sarcosine (a-dp$, flesh) — * 

C 4 H 9 N 3 2 + H 2 = CH 4 N 2 + C 3 H 7 N0 2 

Kreatine. Urea. Sarcosine. 

From the concentrated flesh-extract which has deposited the kreatine, 
there may be obtained, by careful treatment, crystals of a sweet substance 
called inosite or sugar of flesh, and having the composition C 6 H 12 6 .2Aq. 
At a temperature below 212° F, it loses water, and has then the same 
composition as dry grape-sugar, C 6 H 12 6 , with which, however, it is 
certainly not identical. 

Inosite has been obtained in very minute proportion from flesh, but 
unripe beans are said to yield as much as 0*75 rer cent, of this interesting 
sugar. It has also been obtained from the leaves of the walnut-tree, 
which contained, in August, 0*3 per cent, of the dried leaves. 

The saline constituents of the juice of flesh are chiefly phosphates of 
potassium, magnesium, with a little chloride of sodium. It is worthy 
of notice that potassium is the predominant alkali-metal in the juice of 
flesh, whilst sodium predominates in the blood, especially in the serum. 

According to Liebig, the acidity of the juice of flesh is chiefly due to 
the acid phosphate of potassium, KH 2 P0 4 , whilst the alkalinity of 
the blood is caused by sodium phosphate, Na 2 HP0 4 ; and it has been 
suggested that the electric currents which have been traced in the 
muscular fibres are due to the mutual action between the acid juice of 
flesh and the alkaline blood, separated only by thin membranes from each 
other, and from the substance of the muscles and nerves. 

The average composition of flesh may be represented as follows : — 

Water, 78 

Fibrine, vessels, nerves, cells, &c, . 17 

Albumen, ...... 2*5 

Other constituents of the juice of flesh, . 2 - 5 

100-0 
Liebig's extract of meat is prepared by exhausting all the soluble matters 
from the flesh with cold water, separating the albumen by coagulation," 
and evaporating the liquid at a steam heat to a soft extract. It contains 
about half its Aveight of water, 40 per cent, of the organic constituents of 
the juice of flesh (albumen excepted), and 10 per cent, of saline matter. 

Myosine (from fxvs, a muscle) is a constituent of flesh which is liquid 
during life, and coagulates after death. It may be extracted from the 
chopped flesh by water containing y^th of salt, and is precipitated from 
the solution by saturating it with salt. 

Cooking of meat. — A knowledge of the composition of the juice of flesh 
explains the practice adopted in boiling meat, of immersing it at once in 

* Sarcosine has been obtained artificially by the action of chloracetic acid on methyl- 
amine — 

C 3 H 3 C10 2 + NH 2 (CH 3 ) = C 3 H 7 N0 2 + HC1. 
Chloracetic acid. Metliylamine. Sarcosine. 



GELATINE. 621 

boiling water, instead of placing it in cold water, which is afterwards 
raised to the boiling-point. In the latter case, the water would soak into 
the meat, and remove the important nutritive matter contained in the 
juice ; whilst, in the former, the albumen in the external layer of flesh is 
at once coagulated, and the water is prevented from penetrating to the 
interior. In making soup, of course, the opposite method should be fol- 
lowed, the meat being placed in cold water, the temperature of which is 
gradually raised, so that all the juice of flesh may be extracted and the 
muscular fibre and vessels alone left. 

The object to be attained in the preparation of beef -tea, is the extraction 
of the whole of the soluble matters from the flesh, to effect which the 
meat should be minced as finely as possible, soaked for a short time in an 
equal weight of cold water, and slowly raised to the boiling-point, at 
which it is maintained for a few minutes. The liquid strained from the 
residual fibrine contains all the constituents of the juice except the albu- 
men, which has been coagulated. 

When meat is roasted, the internal portions do not generally attain a 
sufficiently high temperature to coagulate the albumen of the juice, but 
the outside is heated far above 212° F.; so that the meat becomes 
impregnated to a greater extent with the melted fat, and some of the 
constituents of the juice in this part suffer a change, which gives rise to 
the peculiar flavour of roast meat. The brown sapid substance thus pro- 
duced has been called osmazome* but nothing is really known of its true 
nature. In salting meat for the purpose of preserving it, a great deal of the 
juice of flesh oozes out, and a proportionate loss of nutritive matter is sus- 
tained. 

435. Gelatine. — When portions of meat, containing cartilages (gristle) 
or tendons, are boiled for some time with water, the liquid so obtained 
sets to a jelly on cooling. This is due to the presence of gelatine or 
chondrine, or both — substances so nearly resembling each other, that they 
were long confounded under the name of gelatine. The difference in their 
origin is that gelatine is obtained by the action of water at a high tem- 
perature on skin, membrane, and bone,+ whilst chondrine is obtained in 
the same way from the cartilages. In their properties there is very little 
difference, the most important being that a solution of chondrine is pre- 
cipitated by acetic acid, by alum, and by lead acetate, which do not pre- 
cipitate gelatine. 

Gelatine mixed with chromate or dichromate of potassium and exposed 
to light, yields an insoluble compound which is turned to account in the 
" carbon process " and some other methods of photography. 

In composition there is a considerable difference between gelatine and 
chondrine, the latter containing considerably more oxygen and less nitro- 
gen. The simplest formulae which have been assigned to them are — 

Gelatine, . . . C'4iU 6 -X 13 16 
Chondrine, . . . G 36 H 9 N 9 16 ; 

but they both contain phosphates of calcium and magnesium in a very 
intimate state of association. 

The characteristic properties of gelatine are the tendency of its solution 
to gelatinise on cooling, and the formation of an insoluble compound with 

* From oa-fxv, odour ; £w/ios, soup. 

f The animal matter of bone appears to be insomeric with gelatine, and is called osseine. 



622 ISINGLASS — SIZE — URINE. 

tannic acid. The latter is the foundation of the art of tanning (page 592), 
and the former is turned to account in the preparation of jelly, size, and 
glue. A solution containing only 1 per cent, of gelatine will set on 
cooling, though if it be repeatedly boiled it loses this property. 

Isinglass is a very pure variety of gelatine prepared from the air-bladder 
of fishes, especially of the sturgeon. 

For the manufacture of glue, the refuse and parings of hides are gene- 
rally employed, after being cleansed from the hair and blood by steeping 
in lime water, and thoroughly exposed to the air for some days, so as to 
convert the lime into carbonate, and prevent the injurious effect of its 
alkaline character upon the gelatine. They are then boiled with water 
till the solution is found to gelatinise firmly on cooling, when it is run 
off into another vessel, where it is kept warm to allow the impurities to 
settle down, after which it is allowed to gelatinise in shallow wooden 
coolers. The jelly is cut up into slices, aud dried upon nets hung up in 
a free current of air. Spring and autumn are usually selected for drying 
glue, since the summer heat would liquefy it, and frost would, of course, 
split it, and render it unfit for the market. 

Size is made in a similar manner, but finer skins are employed, and 
the drying is omitted, the size being used in the gelatinous state. The 
best size is made from parchment cuttings. 

Ey the action of acids or alkalies upon gelatine, two crystalline organic 
bases may be obtained, known by the names of glycocoll, glycocine, or 
sugar of gelatine (C 2 H 5 N0 2 ), and leucine (C 6 H 13 N0 2 ). 

It will be seen that glycocine is isomeric with nitrous ether (C 2 H..N0 2 ),* 
and leucine with the (at present unknown) nitrous ether of the caproic 
series. Leucine has been found in bullock's lungs and in calf's liver. 

A large number of animal substances very nearly resemble gelatine in 
their composition; among these are hair, wool, nails, horns, and hoofs. 

Hair contains, in addition to carbon, hydrogen, nitrogen, and oxygen, 
from 3 to 5 per cent, of sulphur. Wool has sometimes to be separated 
from the cotton in worn-out mixed fabrics. The mixture is plunged into 
diluted hydrochloric acid, dried at 220° F., and submitted to the action 
of a machine {devil), which removes the cotton, rendered brittle by the 
action of the acid, in the form of dust, and leaves the wool fibres 
untouched. When the object is to save the cotton fibre, the fabric is 
exposed to high-pressure steam, which has no action upon cotton, but 
converts the wool into a brown matter easily removed by a beating 
machine, and sold for manure as ulmate of ammonia. 

Silk is said to consist of three layers, the outermost consisting of gela-~ 
tine, and soluble in water ; the next of albumen, soluble in acetic acid on 
boiling ; and the third of a nitrogenised substance called sericine, which is 
insoluble in water and acetic acid. Spider's threads appear to consist of 
this substance. 

Sponge consists of a similar material, which has been called fibroine. 

436. Urine. — The urine of animals is characterised by the presence of 
certain substances which are only met with in very minute quantities, if 
at all, in a state of health, in the other fluids of the body. The most im- 

* Glycocine has been formed by passing cyanogen through a boiling saturated aqueous 
solution of hydriodic acid ; 2CN + 5HI + 2H 2 = C 2 H 5 N0 2 + NH 4 I + I 4 . Tri-lrnetMjl- 
glycocine, C 2 H 2 (CH 3 ) 3 N0 2 or betaine, is found inbeet-root. 



CONSTITUTION OF UEEA. 623 

portant of these are an organic base called urea, uric acid, and Jiippuric 
acid. 

Urea. — When human urine is evaporated to about an eighth of its 
original bulk, and mixed with an equal volume of nitric acid, a semi- 
solid mass is formed, consisting of pearly scales of urea nitrate (CH 4 X 2 0. 
HN0 3 ). If these be washed with cold water, afterwards dissolved in 
boiling water, and treated with barium carbonate, the urea is liberated ; 
2(CH 4 N 2 O.HX0 3 ) + BaO.C0 2 = 2GH 4 X 2 + Ba2X0 3 + H 2 + C0 2 . 

After filtering from the excess of barium carbonate, the liquid is 
evaporated on a water-bath, when a mixture of urea and barium nitrate 
is obtained, from which the urea may be extracted by hot alcohol. On 
evaporating the alcohol, beautiful prismatic crystals of urea are deposited. 
These crystals, when once separated from the urine in a pure state, may 
be preserved indefinitely, even if dissolved in water ; but the urea occur- 
ring in the urine is very soon decomposed, a putrefactive decomposition 
being excited by the mucus, a changeable substance somewhat resembling- 
albumen, which collects in feathery clouds in the urine. The change 
which is thus induced in the urea results in its conversion into ammonium 
carbonate j CH 4 jS t 2 + 2H 2 == (NH 4 ) 2 C0 3 . 

It is in consequence of this change that the urine so soon exhales an 
ammoniacal odour. In order to effect the same change in pure urea, it 
is necessary to heat it with water under high pressure. When urea is 
combined with hydrochloric acid, and the hydrochlorate is heated, it 
furnishes ammonium chloride and cyanuric acid, according to the 
equation; 3(CH 4 X 2 0.HC1) --= 3NH 4 C1 + H 3 C 3 ^ T 3 8 . 

Hydrochlorate of urea. Cyanuric acid. 

When cyanuric acid is distilled, it yields 3 molecules of cyanic acid 
(HCiTO), and the connexion thus established, between urea and the 
cyanogen series becomes intelligible when we see that this base is isomeric 
with ammonium cyanate (]S"H 3 .HCXO). In fact, by combining cyanic 
acid with ammonia, and evaporating the solution, no ammonium cyanate, 
but simply urea, is obtained. 

Upon this has been founded a process for obtaining urea artificially, 
which has attracted a great deal of attention as one of the earliest examples 
of the production, in the laboratory, of a complex substance formed in the 
animal body. For the artificial production of urea, 56 parts of well-dried 
potassium ferrocyanide are intimately mixed with 28 parts of dried man- 
ganese dioxide, and the mixture heated to dull redness in an iron dish, 
and stirred until it ceases to smoulder (see p. 444). The oxygen supplied 
by the oxide of manganese converts the potassium and part of the cyano- 
gen of the ferrocyanide into potassium cyanate, the remainder of the 
cyanogen being burnt, and the iron converted into oxide — 

K 4 (CN) 6 Fe + 9 = 4KCXO + 2C0 2 + X 2 + FeO. 

Potassium Potassium 

ferrocyanide. cyanate. 

On treating the residue with cold water, the potassium cyanate is 
dissolved out, and after the insoluble portion has subsided, the liquid 
may be poured off, and 41 parts of ammonium sulphate dissolved in it. 
Potassium sulphate and ammonium cyanate are thus formed — 

2KCXO + (NH 4 ) 2 .S0 4 = K 2 S0 4 + 2XH 4 CXO; 

and if the solution be evaporated to dryness (on a water-bath) the latter 



624 COMPOUND UEEAS. 

salt is transformed into urea, which may be separated from the potassium 
sulphate by alcohol, which dissolves the urea only.* 

If strong solutions of potassium cyanate and ammonium sulphate be mixed in a 
test-tube and placed in a freezing mixture, potassium sulphate soon crystallises out. 
The solution of ammonium cyanate is poured off and divided into two parts ; one of 
these is boiled for a minute or two to convert the cyanate into urea, which may be 
precipitated by nitric acid. 

By fusing urea with sodium, Fenton has converted it into cyanamide; CON 2 H 4 
+ Na = ]S"aOH + H + NH 2 .CN (cyanamide) ; this is obtained in the pure state by dis- 
solving the mass in water, adding ammonia in excess, and silver nitrate, which gives 
a yellow precipitate ; this is washed, dried, covered with ether, and decomposed by 
H 2 S, when Ag 2 S is separated, and the cyanamide dissolves in the ether, from which it 
may be crystallised. 

437. The true constitution of urea has been the subject of much discussion among 
chemists. The circumstance that, under certain conditions, this base assimilates the 
elements of water and is converted into ammonium carbonate, has led to the opinion 
that urea should be classed among the amides (page 550), when it would be repre- 
sented as derived from ammonium carbonate (NH 4 ) 2 C0 3 by the loss of water, just 
as oxamide is derived from ammonium oxalate — 

(NH 4 ) 2 C0 3 - 2H 2 = CH 4 N 2 ; (NH 4 ) 2 C 2 4 - 2H 2 = C 2 H 4 N 2 2 . 

Ammonium TJ " Ammonium Oxamide 

carbonate. Uiea> oxalate. Uxamide. 

"When ammonium carbonate is heated to 140° C. in a sealed tube, it is converted 
into urea. 

The question naturally presents itself whether the various bases formed by substi- 
tution from ammonia (page 541) would furnish corresponding ureas when acted upon 
by cyanic acid. This has been actually found to be the case ; ethylamine NH 2 (C 2 H 5 ), 
for example, acting upon cyanic acid, yields ethyl-urea, which is isomeric with 
ethylamine cyanate, just as urea is isomeric with ammonium cyanate — 

NH. 2 (C 2 Hg).HCNO = CH 3 (C 2 H 5 )N 2 

Ethylamine cyanate. Ethyl-urea. 

It is evident that if urea be derived from a double molecule of ammonia by the 
substitution of CO for H , then ethyl-urea will be derived in a similar manner from a 
double molecule of ethylamine ; N 2 H 4 (C 2 H 5 ) 2 ; N 2 H 3 (C 2 H 5 )(CO)". 

Ethylamine. Ethyl-urea. 

In this case it will be observed that the diatomic group CO is substituted for one 
atom of the hydrogen, and for one of its representative, ethyle. 

It will be remembered that the amides can be obtained by the action of ammonia 
upon the corresponding ethers ; thus oxalic ether treated with ammonia gives oxamide, 
and the conversion may be intelligibly represented thus — 

(COY') H ^ ( C A)") h 



i5J 2 ~ h; r (C ^M 

Oxalic ether. Ammonia. Oxamide. Alcohol. 

In a similar manner, carbonic ether, when heated in a sealed tube with an 
alcoholic solution of ammonia, yields urea and alcohol — 

rr C n\' 0, + H* I N 2 = H, N 2 + (C jk 2 
(Gft),\ - H -J H - {■■ .« (C 2 H 5 ) 2 j 

Carbonic ether. Ammonia. Urea. Alcohol. 

When cyanic ether (C 2 H 5 .CNO) is acted on by ammonia, -it yields ethyle-urea, the 
action being precisely parallel to that of ammonia upon cyanic acid — 

H.CNO 4- NH 3 = NHg.H.CNO ; (C 2 H 5 ).CNO + NH 3 = NH 3 .(C 2 H 5 ).CNO 
Cyanic acid. Urea. Cyanic ether. Ethyl-urea. 

* Urea has been artificially obtained by Herroun, by passing a mixture of benzene 
vapour, ammonia, and air over red hot platinum wire. Mixter has also produced it by 
passing ammonia and carbon dioxide together through a red hot tube. 



URIC OR LITHIC ACID. 625 

Many other compound ureas of this description have been obtained, in which the 
hydrogen is partly or entirely replaced by the alcohol radicals. The relation existing 
between those and their prototype, urea, will be seen in the following examples : — 

Urea, CH 4 N o ; ethyl-methyl-urea, C(C 2 H 5 )(CH 3 )H 9 N <> ; tetr ethyl -urea, C(C 2 H 5 ) 4 
N 2 ; diphenyl-urea, C(C 6 H 5 ) 2 H 2 N 2 0. 

The supposition that urea is really constituted upon the ammonia type derives 
some confirmation from the circumstance, that a number of substances have been 
obtained which bear the same relation to urea as the amides do to ammonia. They 
are, therefore, sometimes styled ureides, and sometimes compound ureas, in which a 
negative or acid radical occupies the place of a part of the hydrogen. In illustration 
of the mode of formation of the bodies of this class, the production of benzureide or 
benzoyl-urea may be referred to. 

When ammonia acts upon benzoyl chloride, it yields benzamide and hydrochloric 
acid : C 7 H 5 0. CI + NH 3 = C 7 H 5 0. NH 2 + HC1. 

If urea be substituted for the ammonia, benzureide and hydrochloric acid are 
formed ; C 7 H 5 0. CI + CH 4 lSr 2 = C 7 H 5 0. CH 3 N 2 + HC1. Both reactions become much 
more intelligible if urea and its derivatives be allowed to be composed upon the 
ammonia type — 

NH 3 + (C 7 H 5 0)C1 = NH 2 (C 7 H 6 0) + HC1 
Ammonia. chloride! Benzamide. 

NoH 4 (CO)" + (C 7 H 5 0)C1 = N 2 H 3 (C 7 H 5 0)(CO)" + HC1 . 

sassa? B — ide - 

By similar processes, there have been obtained acetyl-urea, N H 3 (C<,H 3 0)(CO)", 
butyryl-urea, N 2 H 3 (C 4 H 7 0)(CO)", &c. 

438. Uric acid. — When human urine is acidified with hydrochloric 
acid and allowed to stand for some time, it deposits minute hard red 
grains, consisting of uric acid (C 5 H 4 N 4 3 ) tinged with the urinary colour- 
ing matter. In urine the acid is present as urate of sodium and urate of 
ammonium, which are often deposited from urine in slight derangements 
of the system, when they are present in excess, -these salts being very 
much more soluble in warm water than in cold. Since uric acid and its 
salts are very common ingredients of calculi, the acid is sometimes called 
lithic acid (\lOos, a stone). 

As the quantity of uric acid in human urine does not exceed 1 grain 
in 1000, recourse is had to other sources for the preparation of this acid, 
which was, at one time, extensively used for the preparation of the 
murexide employed in calico-printing. 

The excrements of the boa-constrictor and of birds, which consist almost 
entirely of acid ammonium urate, and guano, which has been formed by 
the partial decomposition of the excrements of sea-birds, are excellent 
sources of uric acid. The separation of the uric acid from acid am- 
monium urate is easily effected by dissolving it in solution of potash, 
filtering, and adding hydrochloric acid, when the uric acid, which requires 
10,000 parts of cold water to dissolve it, is precipitated as a white 
crystalline powder. 

When a solution of potash is saturated with uric acid in the cold, and 
boiled down out of contact with air, small needle-like crystals are de- 
posited, having the composition K 2 C 5 H 2 N 4 3 , and if this be dissolved in 
water, and carbonic acid gas be passed through the solution, half the potas- 
sium is removed as carbonate, and a granular precipitate of acid potassium 
urate, KHC 5 H 2 N 4 3 is deposited. Uric acid, therefore, is a dibasic acid, 
and the formula of the acid itself (C^H,N,Oo) should be written 
H 2 C 5 H 2 ¥ 4 3 . 

When uric acid is added by degrees to strong nitric acid, it dissolves 

2 R 



626 HIPPURIC ACID. 

with effervescence and evolution of heat ; the solution, on cooling, deposits 
octahedral crystals of a substance called alloxan (C 4 H 2 N 2 4 ), which may 
be represented as formed by the oxidation of the uric acid according to 
the following equation : — 

C 5 H 4 N 4 3 + + H 2 = C 4 H 2 N 2 4 + CH 4 N 2 

Uric acid. Alloxan. Urea. 

Alloxan has the curious property of staining the fingers of a beautiful 
pink colour, and its solution gives an intense purple colour with ferrous 
sulphate. A connexion is established, by means of alloxan, between uric 
acid and urea, which becomes important, because these two bodies, accom- 
panied by a small quantity of alloxan, are always found together in the 
urine. Alloxan appears to be the intermediate stage in the conversion of 
uric acid into urea by oxidation, for if a solution of alloxan be boiled with 
peroxide of lead (Pb0 2 ) carbonic acid gas is evolved, and the alloxan is 
converted into urea by oxidation — 

C 4 H 2 ISr 2 4 + 2Pb0 2 + H 2 = CH 4 N 2 + 3C0 2 + 2PbO . 

Alloxan. " Urea. 

When sulphuretted hydrogen is passed through a solution of alloxan, 
the liquid is troubled by the separation of sulphur, and deposits prismatic 
crystals of alloxantine (C 8 H 4 N 4 7 ) — 

2C 4 H 2 ¥ 2 4 + H 2 S = C 8 H 4 N 4 7 + H 2 + S. 

Alloxan. Alloxantine. 

If 4 grains of alloxantine and 7 grains of crystallised alloxan be dissolved 
in hot water, and 80 grains of a cold saturated solution of ammonium 
carbonate added, carbonic acid gas is disengaged with effervescence, and 
the liquid assumes a brilliant purple colour, depositing as it cools splendid 
crystals, which have a red colour by transmitted light, and reflect a play 
of green and gold, like the wing of the sun-beetle. This magnificent sub- 
stance is known as murexide, and has the formula C 8 H 8 N 6 6 . The beau- 
tiful colour of murexide has been applied to dyeing and calico-printing, 
being prepared for that purpose from the uric acid furnished by guano. 

By acting upon lead urate with methyl e iodide, melhyluric acid, 
C 5 H 3 (CH 3 )]Sr 4 3 , has been obtained as a sparingly soluble crystalline body, 
which yields methylamine, glycocine, ammonia, and carbon dioxide when 
distilled. 

439. Hippuric acid. — Another acid peculiar to the urine, and found 
m very minute quantity in human urine, is hippuric acid (C 9 H 9 N0 3 ), so 
named because it occurs in far larger quantity in the urine of horses (iWos, 
a horse) and cows, the cow's urine yielding more than 1 per cent, of the 
acid. It is generally prepared from cow's urine by evaporating it to about 
an eighth of its bulk, and adding an excess of hydrochloric acid. On 
standing, long prismatic needles of hippuric acid are deposited. It is 
remarkable that this acid can be obtained only from the urine of stall-fed 
cows or of horses kept at rest, for if the animals are actively exercised, 
the above treatment educes benzoic acid (C 7 H 6 2 ) in place of hippuric. 
Again, only the fresh urine yields hippuric acid, for after putrefaction, only 
benzoic acid can be obtained from it. Conversely, if benzoic acid be admin- 
istered to an animal, it makes its appearance as hippuric acid in the urine. 

The relation between these two acids becomes evident when hippuric 
acid is boiled for some time with strong hydrochloric acid ; on cooling, 
the solution deposits crystals of benzoic acid, and if the liquid separated 



ULTIMATE ELEMENTS OF PLANTS. 627 

from these be evaporated, neutralised with ammonia, and mixed with 
alcohol, crystals of glycocine (page 622) are obtained — 

C 9 H 9 IS T 03 + H 2 = C 7 H 6 2 + C 2 H 5 £T0 2 

Hippuric acid. Benzoic acid. Glycocine. 

This result has been confirmed synthetically by acting upon the com- 
pound resulting from the action of glycocine on zinc oxide, with benzoyl- 
chloride (page 481), when hippuric acid is reproduced — 

Zn.2C 2 H 4 N0 2 + 2(C 7 H 5 0.C1) .= ZnCl 2 + 2C 9 H 9 N0 3 

Zinc-glyeocine. Benzoyle chloride. Hippuric acid. 

Hippuric acid, therefore, may be represented as benzoyle-glycocine, 
C 2 H 4 (C r H 5 0)Isr0 2 . A very interesting illustration of the doctrine of 
substitution is connected with these acids. By acting upon hippuric acid 
.with nitric and sulphuric acids, it is converted into nitro-hippuric acid by 
the substitution of JST0 2 for 1 atom of its hydrogen, and if this acid be 
boiled with hydrochloric acid, it yields nitrobenzoic acid, just as hippuric 
yields benzoic acid — ■ 

c »{ no'} m * + H *° = c -{ no:! * + c a no * 

Nitro-hippuric acid. Nitro-benzolc acid. Glycocine. 

In contact with bases, hippuric acid forms salts of the general formula 
M,C 9 H 8 N0 3 , so that the acid itself should be written as HC.jHgiSrOg. 

•In addition to the organic substances which have been already men- 
tioned as occurring in the urine (urea, uric acid, mucus, hippuric acid, 
kreatine), it always contains a large proportion of alkaline and earthy 
salts, especially of sodium chloride, phosphate and sulphate of potassium, 
and phosphates of calcium, magnesium, and ammonium. 

The average composition of human urine may be thus stated — 

Water, 956-80 

Urea, 14-23 

Uric acid, 0-37 

Mucus, 0-16 

Hippuric acid, kreatinine, ammonia, colouring ) .,,„„ 

matter, and unknown organic matters, . \ 

Chloride of sodium, . . . . . . 7 '22 

Phosphoric acid (strictly, P 2 5 ), . . . 2 "12 

Potash, . . 1-93 

Sulphuric acid (strictly, S0 3 ) .• . . . 1 - 70 

Lime, . . . .' . . . . 0*21 

Magnesia., . . . . . . . 0'12 

Soda, 0-05 

999-94 

CHEMISTRY OF VEGETATION. 

440. The ultimate elements of plants, that is, the substances with which 
plants must be supplied in one form or other, to sustain their growth, are 
carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, silicon, 
potassium, sodium, calcium, magnesium, iron, manganese. 

Of these, the carbon, hydrogen, nitrogen, oxygen, sulphur, and phos- 
phorus are grouped together to form the various organic compounds 
furnished by plants, the remaining elements being arranged generally in 
the following forms : — 



628 MINERAL SUBSTANCES OF THE SOIL. 

Chlorides and silicates of potassium and sodium, calcium sulphate, 
phosphates of iron (manganese 1), calcium, magnesium, and ammonium, 
salts of potassium, sodium, and calcium, with vegetable acids. 

Plants are capable of receiving food, either in the form of gas through 
the instrumentality of their leaves, or in solution by their roots. 

The carbon, which is their most important constituent as regards quan- 
tity is taken up in the form of carbonic acid gas by both these organs of 
the plant. This carbonic acid is derived either from the surrounding 
atmosphere, or from the decay of the organic matters contained in the soil 
which surrounds the roots of the plant. 

The hydrogen is derived, partly from water, and partly from the am- 
monia which is carried down to the roots of the plant by rain, or is 
evolved in the putrefaction and decay of the nitrogenised organic matters 
of the soil. The ammonia also forms one great source of the nitrogen in 
plants, another being the nitric or nitrous acid, which is either brought 
down by the rain, or formed within the soil by the nitrification of the 
ammonia (page 133). As to the oxygen, it is obtained both from the 
carbonic acid and water, which contain this element in larger propor- 
tion than is ever present in any vegetable product. The sulphur and 
phosphorus contained in the organic parts of the plant appear to be 
chiefly derived from the sulphates and phosphates of the soil. The 
chlorine, silicon, and the metals are derived from the mineral constituents 
of the soil. 

It is not difficult to imagine the course of formation of a fertile soil from 
a primary rock (of granite, for example) under the influence of the 
atmosphere and rain, exerted through a very long period. 

It will be remembered that granite consists essentially of quartz (silica), 
felspar (silicate of aluminium and potassium or sodium), and mica (silicates 
of aluminium, iron, potassium, and magnesium) ; in addition to these, 
there may always be found in granite minute quantities of calcium phos- 
phate, of sulphates, of chlorides, and of manganese. 

By the disintegration of such rock under the action of air and moisture 
(page 290), a soil will be formed containing the various mineral substances 
required for the food of the plant. If now, upon the thin layer of soil 
thus formed over the face of the rock, some seeds of the lower orders of 
plants, the lichens, for instance, be deposited, they will grow and fructify, 
deriving their carbon, hydrogen, nitrogen, and oxygen from the air and 
rain, and their mineral constituents from the soil. The death of these 
lichens would add new elements of fertility to the soil, in the shape of the 
food which they had condensed from the air, and of the saline ingredients 
which had been converted within their organisations into forms better 
suited to sustain the higher orders of plants. Given, then, the seeds of a 
higher vegetation, a similar process may be supposed to take place, and at 
length animals would be attracted to the spot by the prospect of vegetable 
food, and by transporting to it elements which they had derived from 
other sources, would eventually confer upon it the highest fertility. The 
soil then coming under tillage, the crops raised upon it are consumed by 
animals and removed to a distance, so that the mineral food contained in 
the soil is by degrees exhausted, and unless it is restored the soil becomes 
barren. 

To restore its fertility is the object of manuring, which consists in add- 
ing to the soil some substance which shall itself serve directly as food for 



M 



FOOD FOR PLANTS. 629 

the plant, or shall so modify, by chemical action, some material already 
present in the soil, as to convert it into a state in which the pjant may 
take advantage of it. 

As examples of substances which are added as direct food for plants, 
may be enumerated : — 

(1) The ashes of peat, turf, coal, &c, which furnish the mineral sub- 
stances originally obtained from the soil by the vegetables from which 
these materials were formed. 

(2) Gypsum, or calcium sulphate, and magnesium sulphate, which 
appear to be valuable not only as sources of sulphur, calcium, and mag- 
nesium, but because they are capable of decomposing the ammonium 
carbonate, which is either brought down by rain or evolved by putrefaction 
in the soil, and of converting it into ammonium sulphate which is retained 
in the soil, whereas the carbonate, being a volatile salt, would be again 
exhaled into the air and lost to the plants. 

(3) Phosphate of lime (calcium phosphate), or bone-ash, which is most 
commonly converted into the soluble superphosphate (page 222), by treat- 
ment with sulphuric acid, before being employed as a manure. 

' (4) Sodium chloride, or common salt, serves as a source of sodium, 
for in contact with the calcium carbonate, which is found in all fertile 
soils, it is partly converted into sodium carbonate, which may in turn be 
converted into sodium silicate, or any other salt of sodium necessary to 
the growth of the plant. 

(5) Sodium nitrate (Peruvian nitre) is held to be of great service in 
some cases, as yielding both sodium and nitrogen in a form serviceable to 
the plant. 

(6) The silicates of potassium and sodium, which are especially useful 
to crops containing, like the cereals, a considerable proportion of silica in 
their stems ; since, although that substance is contained in abundance in 
all soils, it is not available for the plant unless converted into a soluble 
state by combination with an alkali. 

(7) Sulphate of ammonia (derived from the gas-works) is, of course, 
useful both for its sulphuric acid and ammonia. 

(8) Plants, or parts of plants, ploughed into a soil, would obviously 
furnish food for other plants by their gradual putrefaction and decay. 

(9) Bones, which furnish carbonic acid and ammonia by the putrefac- 
tion of their gelatinous matter, as well as a large supply of phosphate of 
lime. 

(10) Urine, yielding much ammonium carbonate by the decomposition 
of the urea and uric acid, and an abundance of the phosphates and other 
saline matters required by the plant. 

(11) Solid excrements of various animals, containing the insoluble salts 
(especially phosphates) of the animal's food, as well as easily putrescible 
organic matters yielding much ammonia and sulphuretted hydrogen. 

(12) Guano, the dung of carnivorous sea-birds, which owes its very high 
value partly to the large proportion of urate of ammonia and other nitro- 
genised organic substances which it contains, and partly to the presence 
of phosphates and salts of the alkalies. 

(13) Soot, which appears to act chiefly by virtue of the salts of 
ammonia derived from the destructive distillation of the coal. 

The chief substance employed for acting chemically upon the consti- 
tuents of the soil, so as to render them more serviceable to the plant, is 



630 ROTATION OF CROPS. 

lime, which, modifies in a very important manner both the organic and 
mineral portions of the soil. Its action upon the former consists in pro- 
moting its decay, and the conversion of its elements into those forms, viz., 
carbonic acid, water, ammonia, and nitric acid, in which they may be of 
service to the plant. Upon the inorganic constituents of the soil, lime 
acts by assisting the decomposition of minerals, particularly of those which 
furnish the alkalies (such as felspar), and thus converting them into 
soluble forms. 

In some cases fertility is restored to an apparently exhausted soil, with- 
out the addition of manure, by allowing it to lie fallow for a time, so that 
under the influence of the air and moisture, such chemical changes may 
take place in it as will again replenish it with food available for the crops. 
It is not even necessary in all cases that the soil should be altogether 
released from cultivation; for even though it may refuse to feed any longer 
one particular crop, it may furnish an excellent crop of a different descrip- 
tion, and, which is more remarkable, it may, after growing two or three 
different crops, be found to have regained its power of nourishing the very 
crop for which it was before exhausted. Experience of this has led to the 
adoption of the system of rotation of crops, by which a soil is made to 
yield, for example, a crop of barley, and then successive crops of grass, 
beans, turnips, and barley again. 

The possibility of this rotation is partly accounted for by the difference 
in the mineral food removed from the soil by different crops; thus turnips 
require much of the alkalies and lime ; wheat, much alkali and silica ; 
barley, much lime and silica; and clover, much lime, so that the soil which 
had been exhausted for wheat, because it no longer contained enough 
soluble silica, might still yield sufficient alkali and lime to a crop of turnips, 
and when the alkali was exhausted, might furnish enough lime to a crop 
of clover, after which, in consequence of the chemical changes allowed by 
lapse of time in the soil, more of the original minerals composing it might 
have been decomposed and rendered available for a fresh wheat crop. 

Another explanation of the benefit of systems of rotation may be given 
in those cases in which the refuse of the preceding crop is allowed to 
remain on the land. Some plants extending their roots more deeply into, 
the soil, avail themselves of mineral food which is beyond the reach of 
plants furnished with shorter roots, and when the refuse of the former 
plants is ploughed into the land, the surface is enriched with the food 
collected from the subsoil. 

Our knowledge of the chemical operations taking place in the plant, and 
resulting in the elaboration of the great variety of vegetable products, is 
very slight indeed. We appear to have sufficient evidence that sugar and 
starch, for example, are constructed in the plant from carbonic acid and 
water, that gluten results from the mutual action of the same compounds, 
together with ammonia, or nitric acid, and certain sulphates, and phos- 
phates, but the intermediate steps in this conversion are as yet unknown. 

All seeds contain starch, gluten, or some similar nitrogenised substance 
(legumine, for example), together with mineral matters, these being pro- 
vided for the nourishment of the young plant until its organs are suffi- 
ciently developed to enable it to procure its own food from the air or from 
the soil. During the process of germination, the seed absorbs oxygen and 
evolves carbonic acid gas, and since the albuminous constituent is the 
most mutable substance present, it is probably this which undergoes oxi- 



GROWTH OF PLANTS. 361 

dation, and excites the conversion of the insoluble starch into soluble sugar. 
At this state the seed requires, as is well known, a fair supply of water, the 
elements of which are required for the conversion of the starch (C 6 H 10 O 5 ) 
into sugar (C 6 H 12 6 ) ; water is also required to dissolve the sugar as well 
as the altered albuminous matter and the mineral salts, in order to form the 
sap of the embryo plant. These constituents of the sap, directed by the 
mysterious vital energy in the seed, build up the root, which extends itself 
in search of nourishment down into the soil, and the leaves, which dis- 
charge a similar function with respect to the air. As soon as the leaves 
are developed, the plant becomes able to decompose carbonic acid, water, 
and ammonia, to provide the organic components of its sap. Some part 
of these changes, at least, appears to take place in the leaves of the plant, 
from which, during the day-time, oxygen (together with a little nitrogen) 
is continually evolved. The leaves have been compared to the lungs of 
animals, the functions of which they reciprocate, for whilst, in the lungs 
of animals, an absorption of oxygen and an evolution of carbonic acid gas 
is observed, in the leaves of plants it is the carbonic acid gas which is 
absorbed and oxygen is disengaged. In the dark, plants exhale carbonic 
acid gas, but in much smaller quantity than they decompose in the light. 

That oxygen must be evolved, if plants construct their carbonaceous 
compounds from carbonic acid gas and water, is obvious on reflecting that 
all these compounds contain less oxygen, in proportion to their carbon 
and hydrogen, than is contained in carbonic acid gas and water. 

Thus, we may conceive the formation of all the compounds of carbon 
and hydrogen, or of those elements with oxygen, which are met with in 
plants, by the concurrence, in various proportions, of carbonic acid gas 
and water, and the separation of the whole or a part of their oxygen. 

To take an example : cellulose (C 6 H 10 O 5 ) would result from the coalition 
of 6 molecules of carbonic acid gas and 5 molecules of water, with separa- 
tion of 1 2 atoms of oxygen. Again, malic acid, C 4 H 6 5 , w T ould require 4 
molecules of carbonic acid gas and 3 molecules of water, whilst 6 atoms 
of oxygen would be set free. 

It is equally easy to represent the formation of nitrogenised compounds 
from carbonic acid gas, water, and ammonia, with separation of oxygen, 
for the nitrogen in all such compounds is present in so small a number of 
atoms relatively to the carbon and hydrogen, that the amount of oxygen 
separated from the carbonic acid gas and water, would always far more 
than suffice to convert the whole of the hydrogen of the ammonia into 
water, even if this hydrogen did not itself take part in the formation of 
the compound. Suppose, for instance, that the formation of quinine is 
to be accounted for — 

20CO 2 + 9H 2 + 2NH 3 = C 20 H 24 £T 2 O 2 + 47 . 

Quinine. 

If sulphur be a constituent of the vegetable compound to be formed, it 
is conceivable that the sulphuric oxide derived from the sulphates present 
in the soil should co-operate with the carbonic acid gas, water, and 
ammonia. 

If the composition of gluten be correctly represented by the formula 
C 108 H 169 N 27 O 34 S, the equation explaining its formation from the above 
constituents of the food of the plant would be written — 

108CO 2 + 44H 2 + 27NH 3 + S0 3 = C^H^^S + 229 . 



G32 RIPENING OF FRUITS. 

The chemical tendency of vegetables, therefore, is to reduce to a lower 
state of oxidation the substances presented in their food, whilst animals 
exhibit a reciprocal tendency to oxidise the materials on which they feed. 

With respect to the last stage in the existence of the plant, the ripening 
of the fruit, we know a little more concerning the chemical changes which 
it involves. Most fruits, in their unripe condition, contain cellulose, 
starch, and some one or more vegetable acids, such as malic, citric, tartaric, 
and tannic, the latter being almost invariably present, and causing the 
peculiar roughness and astringency of the unripe fruit. The characteristic 
constituent of unripe fruits, however, is pectose, a compound of carbon, 
hydrogen, and oxygen, the composition of which has not been exactly 
determined. Pectose is quite insoluble in water, but during the ripening 
of the fruit it undergoes a change induced by the vegetable acids, and is 
converted into pectine (C 32 H 40 O 28 ), which is capable of dissolving in water, 
and yields a viscous solution. As the maturation proceeds, the pectine 
itself is transformed into pectic acid (C 16 H 22 15 ), and pectosic acid 
(C 32 H 46 31 ), which are soluble in boiling water, yielding solutions which 
gelatinise on cooling. It is from the presence of these acids, therefore, 
that many ripe fruits are so easily convertible into jellies. 

Whilst the fruit remains green, its relation to the atmosphere appears 
to be the same as that of the leaves, for it absorbs carbonic acid gas, and 
evolves oxygen ; but when it fairly begins to ripen, oxygen is absorbed 
from the air, and carbonic acid gas is evolved, wdiiist the starch and 
cellulose are converted into sugar, under the influence of the vegetable 
acids (page 501), and the fruit becomes sweet. It has been already seen 
that the conversion of starch and cellulose (C 6 H 10 O 5 ) into sugar (C 6 H 12 6 ) 
would simply require the assimilation of the elements of water, so that 
the absorption of oxygen and evolution of carbonic acid gas are probably 
necessary for the conversion of the tannic and other acids into sugar. For 
example — 



C 2 7 H 22^ir + H 2^ 


+ o 24 = 


2C 6 H 12 6 + 15C0 2 ; 


Tannic acid. 




Fruit-sugar. 


3C 4 H 6 8 + 3 = 


^6-^-12^6 


+ 3H 2 + 6C0 2 . 


Tartaric acid. 







When the sugar has reached the maximum, the ripening is completed; 
and if the fruit be kept longer, the oxidation takes the form of ordinary 
decay. 

The scheme of natural chemistry would not be complete unless provi- 
sion were made for the restoration of the constituents of plants, after death, 
to the atmosphere and soil, where they might afford food to new genera- 
tions of plants. Accordingly, very shortly after the death of a plant, if 
sufficient moisture be present, the changeable nitrogenised (albuminous) 
constituents begin to putrefy, and chemical motion being thus excited, is 
communicated to the other parts of the plant, under the form of decay, so 
that the plant is slowly consumed by the atmospheric oxygen, its carbon 
being reconverted into carbonic acid, its hydrogen into water, and its 
nitrogen into ammonia, these substances being then transported in the 
atmosphere to living plants which need them, while the mineral con- 
stituents of the dead plants are washed into the soil by rain. 

Moist wood is slowly converted by decay into a brown substance, which 
has been called humus, and forms the chief part of the organic matter in 
soils. Alkalies dissolve this substance, and on the addition of an acid to 



NUTRITION OF ANIMALS. 633 

the brown solution, a brown precipitate is obtained, which is said to con- 
tain humic, ulmic, and geic acids, but these substances do not crystallise, 
and their existence as definite acids appears to be somewhat doubtful. 
Two other acids of a similar kind, crenic and aprocrenic acids (Kprjvr), a 
well), have been obtained from the same source, and are also found 
occasionally in mineral waters. 

When it is desired to preserve wood from decay, it is impregnated with 
some substance which shall form an unchangeable compound with the 
albuminous constituents of the sap. Kreasote (page 464) and corrosive 
sublimate (Icyanising) are occasionally used for this purpose, the wood 
being made to imbibe a diluted solution of the preservative, either by 
being soaked in it or under pressure. 

In Boucherie's process for preserving wood, the natural ascending force 
of the sap is ingeniously turned to account in drawing up the preservative 
solution. A large incision being made around the lower part of the trunk 
of the growing tree, a trough of clay is built up around it, and filled with 
a weak solution of sulphate of copper, peracetate of iron, or calcium 
chloride. Even after the tree has been felled, it may be made to imbibe 
the preserving solution, whilst in a horizontal position, by enclosing the 
base of the trunk in an impermeable bag supplied with the liquid from a 
reservoir. The impregnation of the wood with such solutions not only 
prevents chemical decay, but renders it less liable to the attacks of insects 
and the growth of fungi. 

NUTBITION OF ANIMALS. 

441. Between the chemistry of vegetable and that of animal life there 
is this fundamental distinction, that the former is eminently constructive 
and the latter destructive. The plant, supplied with compounds of the 
simplest kind — carbonic acid, water, and ammonia — constructs such com- 
plex substances as albumen and sugar; whilst the animal, incapable of 
deriving sustenance from the simpler compounds, being fed with those of 
a more complex character, converts them eventually, for the most part, 
into the very materials with which the constructive work of the plant com- 
menced. It is indeed true, that some of the substances deposited in the 
animal frame, such as fibrine and gelatinous matter, rival in complexity 
many of the products of vegetable life ; but for the elaboration of these 
substances, the animal must receive food somewhat approaching them in 
chemical composition. It is to this nearer resemblance between the food 
of animals and the proximate constituents of their frames, that we may 
partly ascribe the greater extent of our knowledge on the subject of the 
nutrition of animals, which is, however, far from being complete. 

The ultimate elements contained in the animal body are the same as 
those of the vegetable, but the proximate constituents are far more 
numerous and varied. 

The bones containing the phosphates and carbonates of calcium and 
magnesium, together with gelatinous matter, require that the animal should 
be supplied with food which, like bread, contains abundance of phosphates, 
as well as the nitrogenised matter (gluten) from which the gelatinous 
substance may be formed. In milk, the food of the young animal, we 
have also the necessary phosphates, whilst the caseine affords the supply 
of nitrogenous matters. 



634 CHEMISTRY OF DIGESTION. 

Muscular flesh finds, in the gluten of bread and the caseine of milk, the 
nitrogenised constituent from which its fibrine might be formed with even 
less transformation than is required for the gelatinous matter of bone, since 
the composition of fibrine, gluten, and caseine is very similar. The 
albumen and fibrine of the blood have also their counterparts in the 
gluten and caseine of bread and milk, whilst all the salts of the blood may 
be found in either of these articles of food. 

Bread and milk, therefore, may be taken as excellent representatives of 
the food necessary for animals, and the same constituents are received in 
their flesh diet by animals which are purely carnivorous, but the flesh 
contains them in a more advanced stage of preparation. 

It is natural to suppose that those parts of the frame which contain no 
nitrogen should be supplied by those constituents of the food which are 
free from that element, such as the starch in bread and the sugar and fat 
in milk. 

Before the food can be turned to account for the sustenance of the body, 
it must undergo digestion, that is, it must be either dissolved or otherwise 
reduced to such a form that it can be absorbed by the blood, which it 
accompanies into the lungs to undergo the process of respiration, and thus 
to become fitted to serve for the nutrition of the various organs of the 
body, since these have to be continually repaired at the expense of the 
constituents of the blood. 

The first step towards the digestion of the food is its disintegration, 
effected by the teeth with the aid of the saliva, by which it should be 
reduced to a pulpy mass. The saliva is an alkaline fluid characterised by 
the presence of a peculiar albuminous substance called ptyaline (irrvui, to 
spit), which easily putrefies. The action of saliva in mastication is doubt- 
less in great part a mechanical one, but it is possible that its alkalinity 
assists the process chemically, by partly emulsifying the fatty portions of 
the food. The liability of ptyaline to putrefaction favours the supposition 
that it may act in some way as a ferment in promoting the digestion. This 
disintegration of the food is of course materially assisted by the cooking 
to which it has been previously subjected, the hard and fibrous portions 
having been thereby softened. 

The food now passes to the stomach, in which it remains for some time, 
at the temperature of the body (98° F.), in contact with the gastric juice, 
the chief chemical agent in the digestive process. The gastric juice, 
which is secreted by the lining membrane of the stomach, is an acid 
liquid, containing hydrochloric and lactic acids. It is characterised by 
the presence of a peculiar substance belonging to the albuminous class 
of bodies, which is called pepsine (TreVrw, to digest), and possesses the 
remarkable power of enabling dilute acids, by its mere presence, to 
dissolve such substances as fibrine and coagulated albumen, which would 
resist the action of the acid alone for a great length of time. 

An imitation of the gastric juice may be made by digesting the mucous 
membrane of the stomach for some hours in warm very dilute hydrochloric 
acid. The acid liquid thus obtained is capable of dissolving meat, curd, 
&c, if it be maintained at the temperature of the body. The pepsine 
prepared from the stomach of the pig and other animals is sometimes 
administered medicinally in order to assist digestion. 

The principal change which the food suffers by the action of the gastric 
juice is the conversion of the fibrinous and albuminous constituents into 



BILE. 635 

soluble forms (^peptones) ; the starch is also partly converted into dextrine 
and sugar, but the fatty constituents are unchanged. 

The food which has thus been partially digested in the stomach is called 
by physiologists chyme, and passes thence into the commencement of the 
intestines (the duodenum), where it is subjected to the action of two more 
chemical agents, the bile and the, pancreatic juice. 

Bile consists essentially of a solution of two salts known as glycocholafce 
and taurocholate of sodium. Both glycocholic and taurocholic acids are 
resinous, and do not neutralise the alkali, so that the bile has a strong 
alkaline character. Another characteristic feature of this secretion is the 
large portion of carbon which it contains. Glycocholic acid has the 
composition HC 26 H 42 N0 6 , and contains therefore 67 per cent, of carbon, 
whilst taurocholic acid, HC 26 H 44 N0 7 S, contains 61 per cent. The names 
of these acids have reference to the circumstance that they furnish respec- 
tively glycocine and taurine, together with two new acids free from nitro- 
gen, when they are boiled with dilute hydrochloric acid — 

2HC 26 H 42 N0 6 + H 2 = C 48 H 78 9 + 2C 2 H 5 N0 2 

Glycoholic acid. Choloidic acid. Glycocine. 

HC 26 H 44 N0 7 S + H 2 = C 2 H 7 X0 3 S + HC 24 H 3p 5 

Taurocholic acid. Taurine. Cholic acid. 

Taurine forms colourless crystals of great beauty, and is remarkable for 
the large proportion (above 25 per cent.) of sulphur which it contains. 
It also presents an interesting example of a complex animal derivative 
which may be artificially prepared in a very simple manner. 

When olefiant gas is passed over sulphuric anhydride, it is absorbed, 
and if the product be dissolved in water, neutralised with ammonia, and 
evaporated, crystals of ammonium isethionate are obtained — 

C 2 H 4 + S0 3 + NH 3 + H 2 = NH 3 .H 2 O.C 2 H 4 S0 3 

Ammonium isethionate. 

If the corresponding potassium salt be distilled with PC1 5 , it yields 
isethionic chloride, C 2 H 4 S0 2 C1 2 , which, when decomposed by water, gives 
chlorethylsidphurous or chl or ethyls ulphonic acid, C 2 H 4 S0 2 C1(H0), and 
when the silver-salt of this acid is treated with ammonia, it yields taurine — 

C 2 H 4 S0 2 Cl(AgO) + NH 3 = C 2 H 7 N0 3 S + AgCl. 

Taurine is also known as amido-ethyl-sulphonic acid, and is monobasic. 

Another characteristic ingredient of the bile is cholesterine * (C 26 H 44 0), 
a crystalline substance somewhat resembling the fats, and often deposited 
in large quantity in the form of biliary calculi. It has also been found in 
pease, wheat, and some vegetable oils. 

The colouring matter of the bile has never been obtained in a pure state. 

A peculiar substance called glycogen, or animal starch (C 6 H 10 O 5 ), has 
been found in the liver, and becomes speedily converted into sugar after 
death, by assimilating the elements of water. 

The special function of the bile in the digestion of the food has not been 
explained, but from its strongly alkaline reaction it does not appear im- 
probable that its assists in the digestion of fatty substances. 

The pancreatic juice is another alkaline secretion which differs from the 
bile in containing a considerable quantity of albumen, and is very putres- 
cible. Its particular office in digestion appears to consist in promoting 

* From x°^j bile; <rreap,fat. 



636 CHEMISTRY OF NUTRITION. 

the conversion of the starchy portions of the food into sugar (page 501), 
though it also has a powerful action upon the fats, causing them to form 
an intimate mixture, or emulsion, with water, and partly saponifying 
them. The digestion of the starch and sugar is completed by the action 
of the intestinal fluid in the further passage of the food through the 
intestines, so that when it arrives in the small intestines, all the soluble 
matters have become converted into a thin milky liquid called chyle, which 
has next to be separated mechanically from the insoluble portions, such as 
woody fibre, &c, which are excreted from the body. 

This separation is effected in the small intestines by means of two dis- 
tinct sets of vessels, one of which (the mesenteric veins) absorbs the 
dissolved starchy portions of the food, and conveys them to the liver, 
whence they are afterwards transferred to the right auricle of the heart. 
The other set of vessels (lacteals) absorbs the digested fatty matters, and 
conveys them, through the thoracic duct, into the subclavian vein, and 
thence at once into the right auricle of the heart. 

From the right auricle this imperfect blood passes into the right ventricle 
of the heart, and is there mixed with the blood returned from the body by 
the veins, after having fulfilled its various functions in the system. The 
mixture, which has the usual dark brown colour of venous blood, is next 
forced, by the contraction of the heart, into the lungs, where it is distri- 
buted through an immense number of extremely fine vessels traversing the 
lungs, in contact with the minute tubes containing the inspired air, so that 
the venous blood is only separated from the air by very thin and moist 
membranes. Through these membranes the dark venous blood gives up 
the carbonic acid gas with which it had become charged by the oxidation 
of the carbon of the organs in its passage through the body, and acquires, in 
return, about an equal volume of oxygen, which converts it into the bright 
crimson arterial blood. In this state it returns to the left side of the heart, 
whence it is conveyed, by the arteries, to the different organs of the body. 
The chemistry of the changes effected and suffered by the blood in its 
circulation through the body is very imperfectly understood. One of its 
great offices is the supply of the oxygen necessary to oxidise the com- 
ponents of the various organs, and thus to evolve the heat which maintains 
the body at its high temperature. The results of the oxidation of these 
organs are undoubtedly very numerous ; among them we may trace 
carbonic, sulphuric, phosphoric, lactic, butyric, and uric acids, as well as 
urea and some other substances. The destroyed tissues must at the same 
time be replaced by the deposition, from the blood, of fresh particles 
similar to those which have been oxidised. In the course of the blood 
through the circulation, the above products of oxidation have to be removed 
from it — the carbonic acid by the lungs and skin — the sulphuric, phos- 
phoric, and uric acids, and the urea, by the kidneys. 

The various liquid secretions of the body, such as the bile, the saliva, 
the gastric juice, &c, have also to be elaborated from the blood during its 
circulation through the arteries, after which it returns, by the veins, to 
the heart, to have its composition restored by the matters derived from 
the food, and to be reconverted into arterial blood in the lungs. 

When it is remembered that the body is exposed to very considerable 
variations of external heat and cold, a question occurs as to the provision 
made for maintaining it at its 'uniform temperature. This is effected 
through the agency of the fat which is deposited in all the organs of the 



CHEMISTKY OF FOOD. 637 

body. Since fatty substances in general are particularly rich in 'carbon 
and hydrogen, their oxidation within the body would be attended with 
the production of more heat than that of those parts of the organs which 
contain much nitrogen and oxygen. Accordingly, when the body is 
exposed to a low temperature, a larger quantity of its fat is consumed by 
the oxidising action of the blood, and a corresponding increase takes 
place in the amount of heat evolved, thus compensating for the greater 
loss of heat suffered by the body in the cooler atmosphere. Of course, 
in cold weather, when more oxygen is required to maintain the heat of 
the frame, a larger quantity of that gas is inhaled at each breath, on 
account of the higher specific gravity of the air, in addition to which, 
we have the quickened respiration which always attends exposure to 
cold. To supply this extra demand for carbon and hydrogen in cold 
weather, we instinctively have recourse to such substances as fat, starch, 
sugar, &c, which contain them in large proportion, and these aliments, 
free from nitrogen, are often spoken of as the respiratory constituents of 
food; whilst flesh, gluten, albumen, &c, which contain nitrogen, are styled 
the plastic elements of nutrition (7rA.acro-a>, to form). 

Bearing in mind that the food has a twofold office — to nourish the 
frame and to maintain the animal heat — it will be evident that a judiciously 
regulated diet will contain due proportions of these nitrogenous consti- 
tuents, such as albumen, fibrine, and caseine, which serve to supply the 
waste of the organs, and of such non-nitrogenised bodies as starch and 
sugar, from which fat may be elaborated to sustain the bodily warmth. 

The proportion which these two parts of the food should bear to each 
other will, of course, depend upon the particular condition of existence 
of the animal. Thus, for a growing animal, a larger proportion of the 
nitrogenised or plastic portion of food would- be required than for an 
animal whose growth has ceased ; and animals exposed to a low tempera- 
ture would require more of the non-nitrogenised or heat-giving portions of 
the food. 

Accordingly, we find that a man can live upon a diet which contains 
(as in the case of wheaten bread) 5 parts of non-nitrogenised (starch 
and sugar) to 1 part of nitrogenised food (gluten) ; whilst an infant, 
whose increasing organs require more nitrogenised material, thrives upon 
milk, in which this amounts to 1 part (caseine) for every 4 parts of the 
non-nitrogenised portion (milk-sugar and fat). The inhabitants of cold 
climates consume, as is well known, much more oil and fat than those of 
the temperate and hot regions. 

An examination of the composition of different articles of food affords 
us an explanation of the custom which experience has warranted, of asso- 
ciating particular varieties of food. Thus, assuming as our standard of 
comparison the composition of bread, which contains one of nutritive to 
five of heat-giving matter, the propriety of associating the following kinds 
of food will be appreciated : — 



Beef, . 
Potatoes, 


Nutritive. 


Heat-giving 

17 
ID- 


Ham, . 
Veal, . 




S' 

o-i 


Mutton, 
Rice, 




2 7 
12-3 



638 CHANGES AFTER DEATH. 

All muscular or mental exertion is attended with a corresponding 
oxidation of the tissues of the frame, just as each movement of a steam- 
engine may be traced to the combustion of a proportionate quantity of 
coal under the boiler; and hence such exertion both creates a demand 
for food, and quickens the respiration to obtain an increased supply of 
oxygen. 

Experiment has proved that the proportion which the oxygen consumed 
in respiration bears to the carbonic acid gas exhaled, depends very much 
upon the nature of the food. Thus an animal fed upon vegetable matters, 
such as starch and sugar (the oxygen in which exactly suffices to convert the 
hydrogen into water), will turn nearly all the inspired oxygen to account 
in the formation of carbonic acid gas, the volume of which will be nearly 
equal to that of oxygen which disappears at each inspiration; but when 
flesh, or particularly fat, is consumed, much more of the inspired oxygen 
is required to convert the hydrogen of the food into water, so that the 
volume of the carbonic acid gas is far less than that of the oxygen consumed 
in respiration. When an animal has been kept for a length of time 
without food, the proportion between the volume of the carbonic acid gas 
and that of the oxygen consumed is the same as if the animal were being 
fed upon a flesh diet, inasmuch as its own flesh alone is now supporting 
its respiration. 

CHANGES IS THE ANIMAL BODY AFTEE DEATH. 

442. After the death of animals, just as after that of plants, their com- 
ponent parts are reduced to the primary forms from which they were 
derived, so that they may begin again at the foot of the ascending scale 
of life. Very soon after life is extinct, a change takes place in some 
of the nitrogenous constituents, and this change is soon communicated 
to all parts of the body, which undergo a putrefaction or metamor- 
phosis, of which the ultimate results are the conversion of the carbon 
into carbonic acid, the hydrogen into water, the nitrogen into ammonia, 
nitrous and nitric acids, and the sulphur into sulphuretted hydrogen 
and sulphuric acid. The mineral constituents of the animal frame 
then mingle with the surrounding soil, and are ready to take part in 
the nourishment of plants, which construct the organic components of 
their frames from the carbonic acid and ammonia furnished by the 
putrefaction of the animal, and then serve in their turn as sustenance for 
animals whose respiration supplies the air with carbonic acid gas and takes 
in exchange the oxygen eliminated by the plant. 

The functions of the two divisions of animate nature are, therefore, 
perfectly reciprocal, and this relationship must be regarded as the founda- 
tion of economical agriculture. If it were possible to prevent the change 
of the atmosphere, it is quite conceivable that a perpetual succession of 
plants and animals could be raised upon a given farm without any importa- 
tion of food, provided that there was also no exportation. Or even, permit- 
ting an exportation of food, the succession of plants and animals raised upon 
the same land might be, at least, a \erj long one, if the solid and liquid 
excrements of the animals, to feed whom this exportation took place, were 
restored to the land upon which this food was raised. The explanation of 
this is, that the solid and liquid excrements of the animal contain a very 
large proportion of the mineral constituents of the soil, in the very state 



NATURE OF PUTREFACTION". 639 

in which they are best fitted for assimilation by the crop, and as long as 
the soil contains the requisite supply of mineral food, the plant can derive 
its organic constituents from the atmosphere itself. 

Forasmuch, however, as the vegetable and animal food produced upon 
a farm is generally exported to feed the dwellers in towns, whose excre- 
ments cannot, without excessive outlay, be returned to the soil whence 
the food was derived, it becomes necessary for the agriculturist to pur- 
chase farm-yard manure, guano, &c, in order to prevent the exhaustion of 
his soil. A great manufacturing country, in which the majority of the 
inhabitants are congregated in very large numbers around a few centres 
of industry, at a distance from the land under tillage, is thus of necessity 
dependent for a considerable proportion of its food upon more thinly 
populated countries where manufactures do not flourish, to which it exports 
in return the produce of the labour which it feeds. 

The parts of the frames of animals differ very considerably in their 
tendency to putrefaction. The blood and muscular flesh undergo this 
change most readily, as being the most complex parts of the body, whilst 
the fat remains unchanged for a much longer period, and the bones and 
hair will also resist putrefaction for a great length of time. The compara- 
tive stability of the fat is observed in the bodies of animals which have 
been buried for some time in a very wet situation, when they are often 
found converted almost entirely into a mass of adipocere, consisting of 
the palmitic and margaric acids derived from the fat. 

Some evidence has been brought forward of the existence of poisonous 
organic bases (ptomaines or cadaveric alkaloids) in decomposed human 
bodies. 

When an animal body is thoroughly dried, it may be preserved un- 
changed for any length of time, and this is the' simplest of the methods 
adopted for the preservation of animal food, becoming far more efficacious 
when combined with the use of some antiseptic substance, such as salt, 
sugar, spice, or kreasote* The preservative effects of salt and sugar are 
sometimes ascribed to the attraction exerted by them upon moisture, which 
they withdraw from the flesh, whilst spices owe their antiseptic power 
to the essential oils, which appear to have a specific action in arresting 
fermentative change, a character which also belongs to kreasote, carbolic 
acid, and probably to other substances which occur in the smoke of wood, 
well known for its efficacy in curing animal matter. Such substances are 
often called antizymotic bodies ; carbolic, salicylic, benzoic, and boracic 
acids are classed under this head. 

A process commonly adopted for the preservation of animal and vege- 
table food, consists in heating them with a little water in tin canisters, 
which are sealed air-tight as soon as the steam has expelled all the air, 
and if the organic matter be perfectly fresh, this mode of preserving it is 
found very successful, though, if putrefaction has once commenced, to ever 
so slight an extent, it will continue even in the sealed canister quite in- 
dependently of the air. 

Modern experiments have disclosed a great imperfection in our acquaint- 
ance with the conditions under which putrefaction takes place, and 
indicate the presence in the atmosphere of some minute solid patricles 
which appear to be minute ova or germs, and have the power of inducing 
the commencement of this change. It has been found that milk, for 
example, may be kept for a very considerable period without putrefying, 



640 NATURE OF PUTREFACTION. 

if it be boiled in a flask, the neck of which is afterwards loosely stopped 
with cotton wool, whilst, if the plug of cotton wool be omitted, the other 
conditions being precisely the same, putrefaction will take place very 
speedily. 

Perfectly fresh animal matters have also been preserved for a length of 
time in that state, in vessels containing air which has been passed through 
red hot tubes with the view of destroying any living germs which might 
be present, and such substances have been found to putrefy as soon as the 
unpurified air was allowed access to them. 

The extremes of the scale of animated existence would appear to meet 
here. The highest forms of organised matter, immediately after death, 
serve to nourish some of the lowest orders of living germs, these helping 
to resolve the complex matter into the simpler forms of carbonic acid, 
ammonia, &c, which are returned to the atmosphere, the great receptacle 
for the four chief elements of living matter. 



INDEX 



The navies of minerals are printed in italics. 



Abel's experiments on gun-cotton, 508. 
fuze-composition, 365. 
gun-cotton pulp, 508. 
Abietene, 474. 
Aeetal, 556. 
Acetamide, 551. 
Acetates, 565. 
Acetic acid, HC 2 H 3 2 , 471. 

artificial formation, 536. 
formed from alcohol, 498. 
formed from citric, 591. 
glacial, HC 2 H 3 2 , 566. 
purification, 471. 
synthesis of, 536. 
anhydride, C 4 H 6 3 , 567. 
ether, 527. 
oxychloride, 567. 
peroxide, 568. 
Acetification, 498. 
Acetine, 584. 
Acetone, C 3 H 6 0, 566. 

diethylated, 570. 
dimethylated, 571. 
ethylated, 570. 
methylated, 571. 
properties, 566. 
Acetones, 566. 
Acetonitrile, 551. 
Acetyle, 558. 

chloride, 567. 
peroxide, 568. 
urea, 625. 
Acetylene, C 2 H 2 , 92. 

copper test for, 93. 
detection in coal gas, 112. 
formed from defiant gas, 97. 
preparation from coal gas, 93. 

ether, 94. 
properties, 94. 
silver precipitate, 94. 
synthesis, 92. 
Acetylide of copper, preparation, 93. 
potassium, 94. 
sodium, 94. 
Acid, 12. 

definition, 27, 253. 
etymology of, 12. 
of sugar, 586. 
Acids, acrylic series of, CnH.-2n - 2 2 , 578. 
aromatic, 463. 
dibasic, constitution, 252. 
' definition, 86, 253. 
Acids, monobasic, constitution, 140, 250. 
diatomic, 483. 



Acids, monobasic, definition, 253. 
tetrabasic, 117. 
tribasic, 121. 
of the acetic series, 519. 
lactic series, 563. 
organic, constitution, 437, 566. 
oxalic series of, 582. 
polybasic, 528. 
tribasic, constitution, 253. 

definition, 253. 
vegetable, 585. . 
volatile, separation, 571. 
water-type view of, 251. 
Acidulous waters, 50. 
Aconitic acid, 591. 
Aconitine, 540. 
Acridine, 469. 
Acroleine, 577. 
Acrylic acid, HC 3 H 3 2 , 578. 
Actinic rays of light, 150. 
Adapter, 93. • 
Additive formulae, 87. 
Adipic acid, 582. 
Adipocere, 639. 
Aerated bread, 500. 
After-damp, 77. 
Ag, silver, 378. 
AgBr, silver bromide, 384. 
AgCl, silver chloride, 383. 
Agl, silver iodide, 384. . 
AgN0 3 , silver nitrate, 382. 
Ag 2 0, silver oxide, 382. 
Agriculture, economy of, 628. 
Ag 2 S, silver sulphide, 384. 
Agate, 113. 
Aich-metal, 360. 

Air, analysis of, by eudiometer, 36. 
by nitric oxide, 142. 
by phosphorus, 57. 
by pyrogallol, 595. 
atmospheric, 57. 

benzoHsed, for illuminating, 108. 
burnt in coal gas, 106. 
candle test applied to, 77. 
effect of combustion on, 76. 
effect of electric sparks on, 134. 
eudiometric analysis, 36. 
exact analysis by copper, 58. 
germs of life in, 639. 
proportion of ammonia in, 123. 
tested for impurity, 77. 
Al, aluminium, 290. 
A1 2 3 , alumina, 293. 
Alabaster, 278. 

2s 



642 



INDEX. 



Alabaster, oriental, 47. 
Albite, 295. 

Albumen of blood, 618. 
Alcarsin, 532. 
Alcohol, C 2 H 6 0, 521. 
absolute, 522. 
allylic, 486. 
aluminium, 530. 
amylic, C 5 H 12 0, 518. 
anisic, 561. 
benzoic, 500. 
caprylic, 583. 
cerylic, 585. 
chemical constitution, 530. 

definition, 437. 
cuminic, 560. 
flame, 109. 
from milk, 613. 
methylated, 479. 
methylic, CH 4 0, 471. 
radicals, CWH2H+1, 524. 

doubled formulas, 525. 
synthesis, 530. 
water-type view, 530. 
Alcoholic fermentation, 496. 
Alcohols and their derivatives, 517. 
boiling-points, 518. 
diatomic, 561. 
general properties, 518. 
iso-, 517. 
monatomic, 517. 
normal, 517. 

table of, 518. 
polyatomic, 561. 
primary, 517. 
secondary, 517. 
tertiary, 517. 
triatomic, 564. 
vapour-densities, 518. 
Aldehyde, acetic or vinic, C 2 H 4 0, 556. 
ammonia, NH 3 ,C 2 H 4 0, 556. 
benzoic, 560. 
butyric, 558. 
caprylic, 558. 

chemical constitution, 557. 
cinnamic, 560. 
cuminic, 560. 
euodic, 558. 

formation in vinegar-making, 499. 
lauric, 558. 
oenanthic, 558. 
preparation, 556. 
properties, 557. 
propionic, 558. 
pyromucic, 569. 
resin, 557. 
rutic. 558. 
salicylic, 560. 
valeric, 558. 
Aldehydes, 437, 556. 

action on amines, 558. 
derivation from alcohols, 519. 
Aldol, 557. 

Ale, composition, 497. 
Algaroth, powder of, 341. 
Alizarine, artificial, 604. 

orange, 604. 
Alkali, definition, 12. 

manufacture, 262. 
metals, group of, 254. 
works, fumes from, 158. 



Alkaline earth metals, general review, 280. 
Alkaloids, constitution, 540. 
Alkaloids, constitution determined, 545. 
organic, 540. 

vegetable, extraction of, 596. 
Allotropy, 192. 
Alloxan, C 4 H 2 N 2 4 , 626. 
Alloxantine, C 8 H 4 N 4 7 , 626. 
Allyle, C 3 H 5 , 485. 
iodide, 486. 
series. 485. 
sulphide, 486. 
sulphocyanide. 486. 
ter bromide, 578. 
Allylene, 487. 
Allylic alcohol, 486. 

aldehyde, 578. 
Almond cake, 480. 

oil, 583. 
Almonds, 480. 
Aloes, 487. 
Aludels, 385. 
Alum, 291. 

basic, 292. 
concentrated, 291. 
in bread, 501. 
shale, 291. 
uses, 292. 
Alumina, A1 2 3 , 293. 
Aluminium, Al, 290. 

acetate, 565. 
action on water, 13. 
and copper, 295. 
bronze, 360. 
chloride, A1 2 C1 6 , 293. 
ethide, 537. 
extraction, 294. 
hydrate, 293. 
methide, 537. 
phosphates, 296. 
properties, 294. 
silicates, 295. 
silicide, 118. 
sulphates, 291. 
Alums, 211. 
Alunogen, 291. 

Amalgam, for electrical machines, 386. 
of ammonium, 130. 
of sodium, 130. 
Amalgamating zinc plates, 386. 
Amalgamation of gold ores, 401. 

of silver ores, 379. 
Amalgams, 386. 
A marine, 569. 
Amber, 478. 
Amethyst, 113. 
Amides, constitution, 550. 
formation, 551. 
of phosphoric acid, 236. 
Amidide of potassium, 553. 
Amido-diphenylimide, 463. 

ethyl-sulphonic acid, 635. 
Amidogen, NH 2 , 551. 
Ammonia, NH 3 , 123. 

absorbed by charcoal, 66. 

absorption by water, 125. 

action of iodine on, 180. 

-alum, 292. 

and chlorine, 152. 

arsenite, 240. 

as food for plants, 124. 



INDEX. 



643 



Ammonia, bicarbonate, 269. 

bi-hydrosulphate, 271. 
burnt in oxygen, 129. 
carbonate, (NH 4 ) 2 C0 3 , 269. 
combination with acids, 130. 
connnon carbonate, 268. 
composition, 129. 
decomposed by the spark, 129. 
delicate test for, 390. 
derivatives, 438. 
explosion with oxygen, 133. 
formation from nitric acid, 138. 
gas, dried, 128. 

preparation, 124. 
group of hydrogen compounds, 

243. 
hydriodate, 271. 
hydrobromate, 271. 
hydrochloride, NH 3 .HC1, 130. 
properties, 270. 
hydrosulphate, NH 3 .H 2 S, 270. 
hyposulphite, 271. 
identified, 125. 

in waters, examination for, 390. 
isethionate, 635. 
liquefied, 127. 
molybdate, 334. 
muriate, 269. 
Nessler's test for, 390. 
nitrate, 140. 

decomposed by heat, 140. 
preparation, 140. 
nitrification of, 132. 
oxalate, (NH 4 ) 2 C 2 4 , 587. 
properties, 125. 
proportion in air, 123. 
salts, 268. 

sesquicarbonate, 268. 
soda-process, 264. 
solution, determination of 

strength, 126. 
solution, specific gravity, 126. 
sources of, 123. 
sulphate, (NH 4 ) 2 S0 4 , 268. 
urate, 625. 
volcanic, 266. 
Ammoniacal liquor, 453. 

extraction of ammonia 
from, 124. 
Ammoniacum, 487. 
Ammonia-meter, 126. 
Ammonias, complex, 541. 

ethylated, 541. 
Ammoniated chloride of silver, 127. 
Ammonide, sulphuric, (NH 3 ) 2 S0 3 , 268. 
Ammonium, NH 4 , 268. 
alum, 292. 
amalgam, 130. 
arsenite, 240. 
bisulphide, 271. 
bromide, 271. 
carbonate, 269. 
chloride, 269. 

properties, 270. 
heptasulphide, 271. 
iodide, 271. 
molybdate, 334. 
nitrate, 140. 
oxalate, 587. 
pentasulphide, 271. 
salts, 268. 



Ammonium, sulphate, 268. 

sulphide, (NH 4 ) S, 270. 

yellow, 271. 
sulphocyanide, prepared, 217- 
Ammonium theory, 130. 

tri-iodide, 181. 
Amorces, 228. 
Amorphous, 62. 
Amorphous phosphorus, 224. 
Amygdaline, 480. 
Amylacetic (oenanthic) acid, 570. 
Amylamine, 543. 
Amyle, C 5 H n , 526. 
acetate, 556. 
valerianate, 556. 
Amylene, 521. 
Amylene-glycol, 564. 
Amylethylic ether, 531. 
Amylic alcohol, C 5 H 12 0, 518. 
Amylic iodide, 525. 

Analysis of gaseous hydrocarbons, 110. 
of marsh gas, 111. 
organic, 84. 

calculation of, 85. 
Anatase, 350. 
Ancaster stone, 412. 
Anchoic acid, 582. 
Angelic acid, 578. 
Ancjlesite, PbO.S0 3 , 366. 
Anhydride, acetic, 566. 

benzoacetic, 567. 
benzoic, 481. 
carbonic, 86. 
defined, 25. 
lactic, 613. 
nitric, 139. 
phosphoric, 230. 
sulphuric, 210. 
sulphurous, 198. 
tartaric, 588. 
Anhydrides of organic acids, 566. 
Anhydrite, 279. 
Anhydrous, 40. 
Aniline, C 6 H 7 N, 4*9. 
black, 462. 
blue, 461. 

constitution, 547. 
colours, 460. 
constitution, 547. 
-green, 462. 
-purple, 460. 
-red, 460. 

constitution, 547. 
salts, 462. 
test for, 460. 
-violet, 462. 

constitution, 548. 
-yellow, 461. 
Animal charcoal, 67. 

chemistry, 611. 
heat, 637. 
Animals and plants, reciprocity of, 633. 
changes after death, 638. 
destructive functions of, 633. 
nutrition of, 633. 
oxidising functions of, 636. 
ultimate elements of, 633. 
Animi resin, 478. 

Aniseed, essential oil of, 482, 560. 
Anisic acid, 482, 561. 
alcohol, 561. 



644 



INDEX. 



Anisyle hydride, 482, 560. 
Annatto, 603. 

Ansell's fire-damp indicator, 99. 
Anthracene, 469. 
Anthracite, 70, 433. 

composition, 71, 433. 
production of flame from, 88. 
Anthrapurp urine, 604. 
Anthraquinone, 604. 
Antichlore, 201, 212. 
Anticorrosive caps, 165. 
Antimonic oxide, Sb 2 O g , 339. 
Antimonietted hydrogen, 340. 
Antimony, Sb, 337. 

action on water, 13. 

amorphous, 338. 

antimoniate, 339. 

"butter of, 341. 

chlorosulphide, 341. 

crocus, 338. 

crude, Sb 2 S 3 , 338. 

detected, 197, 340. 

extraction in the laboratory, 

338. 
edass of, 342. 
grey ore of, Sb 2 S 3 , 337. 
ore, red, Sb 2 3 , 2Sb>S 3 , 342. 

white, Sb 2 3 , 339. 
oxide, Sb 2 3 , 339. 
oxychloride, 341. 
oxysulphide, 342. 
pentachloride, SbCl 5 , 341. 
pentasulphide, Sb 2 S 5 , 342. 
potassio-tartrate, 588. 
regulus, 338. 
sulphide, Sb 2 S 3 , 341. 
sulphide identified, 341. 
sulphides, 341. 
tested for lead and iron, 342. 
trichloride, SbCl 3 , 341. 
uses, 338. 

vermilion, 214, 342. 
Antiseptic properties of boracic acid, 121. 
carbolic acid, 465. 
kresylic acid, 466. 
sulphurous acid, 
201. 
Antizymotics, 639. 
Ants, acid of, 568. 

oil of, 569. 
Apatite, 222. 
Apocrenic acid, 633. 
Apomorphine, 597. 
Apple oil, 556. 

Aq., water of crystallisation, 42. 
Aqua fortis, 136. 
regia, 172. 
Arabine, 489. 

Arachidic (butic) acid, 520. 
Arbor Dianse, 387. 
Archil, 606. 
Argand lamp, 107. 
Argent-ethenyle, chloride of, 94. 

oxide of, 94. 
Argent- allylene, 487. 
-ethenyle, 94. 
Argillaceous iron ores, 300. 
Argol, 257, 588. 
Aromatic nucleus, 459. 

series, 459. 
Arrack, 516. 



Arragonite, CaC0 3 , 277. 
Arrowroot, 492. 
Arsenites, 240. 
Arsenic, As, 236. 

combining volume, 236. 

detection, 242. 

di-iodide, 244. 

extraction, 237. 

extraction from organic matters, 

244. 
in copper, 358. 
native, 236. 
oxides, 238. 
pentasulphide, 245. 
subsulphide, 244. 
sulphide, identified, 245. 
sulphides, 244. 
tribromide, 244. 
chloride, 243. 
ethoxide, 536. 
fluoride, 244. 
iodide, 244. 
white, 238. 
Arsenic acid, H 3 As0 4 , 241. 

action of hydrosulphuric acid 
on, 245. 
Arsenical nickel, NiAs 2 , 326. 
paper-hangings, 241. 
pyrites, 236. 
soap, 240. 
Arsenic eating, 241. 
Arsenides, 236. 
Arsenietted hydrogen, AsH 3 , 242. 

decomposed by heat, 
243. 
Arsenio-diethyle, 536. 
-dimethyle, 536. 
-sulphides, 237. 
-triethyle, 536. 
-trimethyle, 536. 
Arsenious anhydride, As 2 3 , 240. 

action of ammonia on, 240. 
chlorine on, 243. 
hydrochloric acid 

on, 244. 
hydrosulphuric acid 
on, 245. 
behaviour with water, 239. 
composition, 240. 
crystalline, 239. 
identified, 239. 
opaque, 239. 
smallest fatal close, 239. 
vitreous, 239. 
Arseniuretted or arsenietted hydrogen, 242. 
As, arsenic, 236. . 
Asafoetida, 487. 

essential oil of, 485. 
Asbestos, 281. 

AsH 3 , arsenietted hydrogen, 242. 
Ashes of coal, 71. 
As 2 3 , arsenious- oxide, 238. 
As 2 5 , arsenic oxide, 241. 
Asparagine, 592. 
Asparagus, 506. 
Aspartic acid, 592. 
Asphaltum, 473. 

Assay of gold by cupellation, 401. 
Atacamite, 363. 
Atmolysis, 21. 
Atmosphere, composition, 57. 



INDEX. 



645 



Atmospheric air, 57. 

Atmospheric germs of putrefaction, 639. 

Atom, definition, 2. 

Atomic formulas, types of, 247. 

Atomic heat, 280. 

Atomic heats, 280. 

of compound "bodies, 281. 
potassium, sodium, and 
lithium, 280. 
Atomicities, classification by, 247. 
Atomicity, 247. 

importance in theory, 248. 

notation of, 249. 
Atomic theory, 2. 
weight, 3. 

of sulphur, 194. 
Atropine, 540. 

Attraction, chemical, definition, 5. 
An, gold, 400. 

AuCl 3 , gold trichloride, 404. 
Augite, 296. 
Auric oxide, Au 2 3 , 404. 
Aurine, 466. 

Autogenous soldering, 204. 
Avogadro's law, 1. 
Azobenzide, 459. 
Azodinaphthylamine, 467. 
Azolitmine, 606. 
Azote, etymology, 123. 

B, BORON, 119. 

Ba, barium, 274. 
BaCl 2 , barium chloride, 275. 
BaC0 3 , barium carbonate, 275. 
Baking powders, 80. 
Balenic acid, 520. 
Balloons, 16. 

made, 514. 
Balsam of Peru, 477. 
Tolu, 477. 
Balsams, 477. 
Banca tin, 344. 

Ba(N 3 ) 9 , barium nitrate, 275. 
BaO, baryta, 275. 
Barilla, 262. 
Bar-iron, best, 312. 

composition, 312. 

crystalline, 314. 

fibrous, 314. 

manufacture, 308. 
Barium, Ba, 274. 

action on water, 13. 

binoxide, 275. 

carbonate, 275. 

chlorate, 276. 

chloride, BaClo, 275. 

hydrate, 275. ' 

hypophosphite, 232. 

nitrate, Ba(N0 3 ) 2 , 275. 

sulphate, 274. 

sulphide, 274. 

sulphovinate, 528. 
Barley sugar, 505. 
Baryta, BaO, 275. 

carbonate, 275. 

preparation from heavy 
spar, 275. 

chlorate, 276. 

hydrate, BaO.H 2 0, 275. 

in glass, 408. 

sulphate, 274. 



Baryta, sulphate, decomposition, 275.' 

Barytocalcite, 277. 

Basalt, 296. 

Base, definition, 28. 

Basicity of acids determined, 251. 

Basic oxides, 28. 

BaS0 4 , barium sulphate, 274. 

Bassorine, 490. 

Basylous, 246. 

Bathgate coal, 472. 

Bath stone, 412. 

Baths, photographic, recovery of silver 

from, 383. 
Battery, galvanic, 7. 
Baume's flux, 417. 
Bauxite, extraction of aluminium from, 

294. 
Baysa'lt, 261. 
Beans, inosite in, 620. 
Bear, 335. 
Beef-tea, 621. 
Beehive-shelf, 11. 
Beer, composition, 497. 
ropy, 498. 
sparkling, 8U. 
Bees' wax, 585. 
Behenic acid, 520. 
Bell-metal, 347. 
Bengal saltpetre, KN0 3 , 413. 
Benic acid, 520. 
Benzamide, 551. 
Benzene, C 6 H 6 , 458. 
Benzene sulphonic acid, 464. 
Benzoacetic anhydride, 567. 
Benzoic acid, HC 7 H 5 2 , 479. 

in cow's urine, 626. 
alcohol, 481, 560. 
anhydride, 481. 
peroxide, 567. 
Benzoin, gum, 479. 
Benzoine, 481. 
Benzole or Benzine, C 6 H 6 , 458. 

action of nitric acid on, 139. 
chloride, 458. 
Benzoline, 456. 
Benzolised air, 108. 
Benzone, 560. 
Benzonitrile, 551. 
Benzophenone, 560. 
Benzoyle, C 7 H 5 0, 481. 

compounds, 481. 

glycocoll, 627. 

hydride, 480. 

peroxide, 567. 

salicylamide, 552. 

salicyle, 483. 

series, 481. 
Benzoyle-urea, 625. 
Benzureide, 625. 
Benzylamine, 560. 
Benzyle, chloride, 560. 
Bergamotte, essential oil of, 476. 
Beryl, 290. 

Bessemer's process (iron), 313. 
Betaine, 622. 
Bezoars, 594. 
Bi, bismuth, 335. 
Bibasic acids, constitution, 252. 
Biborate of soda, 266. 
Bibromosuccinic acid, 589. 
Bicarbonate of soda, NaHC0 3 , 265. 



646 



INDEX. 



Bicarbonates, 86. 
Bichloracetic acid, 566. 
Bi-equivalent elements, 247. 
Bile, 635. 
Bimetantimoniate of potash, 339. 

soda, 339. 
Binoxide of hydrogen, 53. 
nitrogen, 141. 
Bi 2 3 , bismuthic oxide, 336. 
Birch, essential oil of, 476. 
Bi 2 S 3 , bismuthic sulphide, 337. 
Biscuit porcelain, 410. 
Bismuth, Bi, 335. 

action on water, ] 3. 
glance, 337. 
impurities, 336. 
nitrate, Bi(N0 3 ) 3 , 337. 
ochre, 336. 
oxides, 336. 
oxychloride, 337. 
sulphide, 337. 
telluride, 220. 
trichloride, BiCl 3 , 337. 
trisnitrate, 337. 
Bismuthic acid, 336. 
Bismuthite, 337. 
Bistearine, 576. 

Bisulphate of potash, KHS0 4 , 135. 
Bisulphide of carbon in coal gas, 217. 
Bisulphites, 201. 
Bisulphuret of carbon, 215. 
Bitter almond oil, C 7 H 6 0, 480. 
Bittern, 172, 261. 
Bitumen, 473. 
Bituminous coal, 70. 
Bixine, 603. 
Black ash, 263. 

Black ash liquor, treatment, 263. 
Blackband, 300. 
Black dyes, 610. 
Blacking, vitriol in, 208. 
Black lead, 63. 

crucibles, 63. 
vitriol, 363. 
wash, 390. 
Blast-furnace, 302. 

chemical changes in, 303. 
gases, 304. 
Blasting-gelatine, 581. 
Blasting with gunpowder, 427. 
Bleaching by chloride of lime, 155. 
chlorine, 154. 
ozone, 55. 

sulphurous acid, 200. 
powder, 155. 
Bleach killed, 201. 
Blende, ZnS, 285. 
Blistered steel, 316. 
Block tin, 345. 
Blood, 615. 

action of oxygen on, 617. 
aeration of, 617. 
coagulation of, 615. 
crystals, 617. 
defibrinated, 616. 
formation from food, 634, 636. 
globules, 616. 
venous and arterial, 617. 
Bloom (iron), 311. 
Bloomery forge, 320. 
Blowers in coal-mines, 98. 



Blowpipe, cupellation with, 372. 
flame, 109. 
hot-blast, 110. 
oxyhydrogen, 39. 
reduction of metals by, 109. 
table, 117. 

test for lithium, 271. 
test for potassium, 259. 
sodium, 265. 
Blue bricks, 411. 
copperas, 362. 
dyes, 609. 

fire composition, 165. 
. flowers, colouring matter of, 603. 
malachite, 353. 
metal (copper), 357. 
oxide of molybdenum, 334. 

tungsten, 351. 
pill, 386. 
pots, 63. 

Prussian, Fe 4 Fcy 3 , 441. 
stone, 362. 
Thenard's, 325. 
Turnbull's, 446. 
verditer, 363. 
vitriol, 362. 

water of copper mines, 357. 
writing paper, 296. 
B 2 3 , boracic anhydride, 119. 
Bog-butter, 474. 
Boghead cannel, 472. 
Boiler fluid, arsenical, 240. 

incrustations, 46. 
Boiling meat, 620. 
Boiling-point, definition, 52. 
Boiling-points of benzene series, 454. 
Boiling process (iron), 313. 
Bolivite, 337. 
Bolsover stone, 412. 
Bone-ash, 222. 

as manure, 629. 
black, 67. 

earth, as manure, 629. 
formation from food, 633. 
Bones, ammonia furnished by, 548. 
as manure, 629. 
composition, 222. 
destructive distillation, 67. 
Boracic acid, H 3 B0 3 , 119. 
crystals, 120. 
identified, 121. 
in glass, 408. 
manufacture, 120. 
tribasic, 121. 
vitreous, 121. 
anhydride-, 119. 
ether, 527. 
lagunes, 120. 
Boracite, 283. 
Borates, 120. 

Borax, Na 9 0.2B 2 3 , 119, 266. 
glass, 267. ' 
identified, 267. 
manufacture, 266. 
refining, 266. 
uses, 267. 
vitrified, 267. 
Boric ethide, 537. 

methide, 537. 
Borneene, 477. 
Borneo camphor, 477. 



INDEX. 



6-i' 



Borofluoric acid, 186. 
Boroflnorides, 186. 
Boroglvceride, 576. 
Boron,"B, 119. 

amorphous, 122. 

chloride, BC1 3 , 171. 

crystallised. 122. 

diamond, 122. 

fluoride, BF 3 , 186. 

graphitoid, 122. 

nitride, 122. 

trichloride, 171. 

trifluoride, 186. 
Botany Bay gum, 465. 
Boucherie's process for preserving 

633. 
Bouquet of wines, 516. 
Boyle's fuming liquor, 271. 
Br, bromine, 172. 
Brandv. 516. 
Brass/ 360. 

for engraving, 360. 

guns, 316. 

preparation, 360. 
Brassic acid, 578. 
Bra unite. Ain.>0 3 , 328. 
Brazil wood, 603. 
Bread, 199. 

aerated, 500. 

new and stale. 501. 
Brewing, 195. 
Bricks, 411. 

efflorescence on, 267. 
Bright iron, 307. 
Brimstone, 188. 
Britannia metal, 316. 
British brandy, 516. 

gum, 492. 
Brochantite. 363. 
Bromates, 174. 
Bromic acid, 174. 
Bromine, Br, 172. 

action on potash, 173. 
chloride of, 175. 
etymology, 173. 
hydrate, 173. 
identified, 173. 
in waters, 172. 
useful applications, 173. 
with hydrogen, 174. 
Bromoform, 554/ 
Bromosuccinic acid, 590. 
Bronze, 347, 360. 

annealing of, 347. 

coin, 347. 

powder, 319. 
Bronzing. 360. 
Brookite, 350. 
Brown acid (sulphuric), 207. 

blaze, 289. 

coal, 70. 

dyes, 610. 

hcematite, 300. 
Brucine, 510. 
Brudte, 283. 
Brunolic acid, 454. 
Brunswick green, 363. 
Bubbles, explosive, 31. 
Buckskin, 593. 
Bug-poison, 389. 
Building-materials, 411. 



Building stone, effect of air of towns on. 112. 

preservation of, 412. 
Bullets, rifle, 372. 

shrapnel, 372. 
Burner, air-gas, 107. 
Bunsen's, 107. 
gauze, 107. 
hot-air, 107. 
ring, 51. 
rosette, 51. 
Burners, smokeless, 107. 
Burnett's disinfecting fluid, 2S9. 
Butic acid, 520. 
Butine, 581. 
wood, Butter, 584. 

Butter-milk, 612. 

preparation of, 612. 
Butylactic acid, 563. 
Butvlamine, 548. 
Butyle, C 4 H 9 , 525. 
-amyle, 525. 
-caproyle, 525. 
-sulphocyanide, 486. 
Butylene, 521. 

-glycol, 564. 
Butylic alcohol, 518. 
Butvramide, 551. 
Butyric acid, HC 4 H 7 2 , 519, 569. 

formed from citric, 591. 
synthesis of, 570. 
two rational formulas of, 570. 
ether, 556. 
Butyrine, 584. 
Butyrone, 559. 
Butyryle, 55 8. 

-urea, 625. 



, C, carbon, 61. 
J Ca, calcium, 276. 
' Cacao-butter, 600. 
j CaClo, calcium chloride, 279. 
j CaC0 3 , calcium carbonate, 277. 
\ CaC 2 4 , calcium oxalate, 587. 
Cadaveric alkaloids, 639. 
Cadet's fumina; liquor, 532. 
Caclniia, CdS, 289. 
Cadmium, Cd, 289. 

carbonate, 289. 
identified. 289. 
iodide, 2S9. 
oxide. 2S9. 
sulphide, CdS, 289. 
Caesia, 273. 

Caesium carbonate, 273, 279. 
platinochloride, 395. 
j Caen-stone, 112. 
CaFo, calcium fluoride, 181. 
Caffeic acid, 599. 
Caffeine, C 8 H l0 X 4 O 2 , 599. 

chemical constitution, 600. 
extraction of, 599. 
formed from theobromine, 600. 
Caffeol, 599. 
Cairngorm stones, 113. 
Caking-coal, 71. 
Calamine, ZnC0 3 285. 
electric, 285. 
Calcareous waters, 47. 
Calcium, Ca, 276. 

action on water, 11. 
bimalate, 591 



648 



INDEX. 



Calcium, bisulphide, 198. 

carbonate, CaC0 3 , 277. 

chloride, CaCl 2 , 279. 

fluoride, CaF , 181. 

hydrate, Ca(HO) 2 , 278. 

hypochlorite, 162. 

hyposulphite, 212. 

lactate, 612. 

oxalate, CaC 2 4 , 587. 

oxy chloride, 155, 279. 

pentasulphide, 198. 

phosphide, 235. 

sulphate, CaS0 4 , 278. 

sulphide, 279. 
Calc-spar, 277. 
Calculation of formulae, 85. 
Calico-printing, 610. 
Calomel, HgCl, 389. 
Calorific instensity, 431. 
Calx chlorata, 162. 
Cameos, 113. 

Camomile, essential oil of, 476. 
Camphilene, 475. 
Camphine, 475. 
Camphor, CjoHjgO, 477. 
artificial, 475. 
oil of, 477. 
Camphoric peroxide, 475. 
Camphorimide, 552. 
Camphors, 477. 
Candle, chemistry of, 103. 
Candles, 574. 

composite, 574. 
Cane-sugar, C 12 H 22 O n , 503. 

action of yeast on, 496. 
composition, 506. 
Cannel, 71. 

Cannel gas, composition, 112. 
Canton's phosphorus, 279. 
CaO, lime, 277. 

CaO.COo, carbonate of lime, 277. 
CaO.O, oxalate of lime, 587. 
CaO.SOg, sulphate of lime, 278. 
Caoutchine, 488. 
Caoutchouc, 487. 

artificial, 583. 
in plant juices, 487. 
solvents for, 487. 
Cap composition, 449. 
Capric (rutic) acid, 519. 
Caprine, 584. 
Caproic acid, 519. 

alcohol, 518. 
Caproine, 584. . 
Caproyle, C 6 H 13 , 525. 
Caproylene, 521. 
Caprylic acid, 519, 

alcohol, 518. 
Capsicine, 540. 
Caramel, 505. 
Carbamates, 269. 
Carbamic acid, 269. 
Carbamines, 552. 
Carbazotic acid, 465. 
Carbinol, 521. 
Carbodiamine, 443. 
Carbolic acid, C 6 H 6 0, 464. 

antiseptic character, 465. 
tests of purity, 464. 
Carbon, C, 61. 

and hydrogen, 92. 



Carbon and oxygen, 72. 
atomicity, 248. 
atomic weight, 92 
bichloride, CC1 4 , 169. 
bisulphide, CS 2 , 215. 
uses, 217. 
burnt to carbonic oxide, calorific 

value of, 433. 
calorific intensity calculated, 431. 
calorific value, 429. 
chemical relations of, 68. 
chlorides of, 168. 

composition by volume, 
170. 
circulation in nature, 72. 
determination of, 84. 
disulphide, 215. 
group of elements, 122, 246. 
iodide, 180. 

liquid sesquichloride, CC1 3 , 170. 
natural sources 61. 
oxides of, 72. 
oxychloride, COCl 2 , 170. 
oxysulphide, 218. 
physical properties, 65. 
protochloride, C 2 C1 4 , 169. 
sesquichloride, C 2 C1 6 , 168. 
subchloride, C 2 C1 2 , 169. 
tetrabromide, 175. 
use in metallurgy, 69. 
Carbonate of baryta and lime, 277. 
lime and soda, 277. 
lime in waters, 46. 

natural sources of, 73. 
Carbonates, 86. 

additive formulae, 87. 
alkaline, 274 
normal, 251. 

substitutive formulae, 87. 
Carbonic acid gas, C0 2 , 72. 

absorption by water, 79. 
analysis of, 87. 
composition by volume, 

91. 
decomposed bv carbon, 
88. 
potassium, 87. 
determination of, 83. 
evolved by plants, 72. 
experiments with, 74. 
formation of propylic acid 
x from, 536. 

formed in combustion, 72. 
respiration, 727 
in air, sources of, 72. 
in breathed air, 77. 
injurious effects of, 76. 
liquefaction of, 81. 
preparation, 73. 
properties, 73. 
separation from other 
. gases, 83. 
Carbonic acid springs, 73. 

synthesis of, 61. 
Carbonic anhydride, 86. 

ether, 528. 
Carbonic oxide, CO, 88. 

absorption by cuprous chlo- 
ride, 249. 
action on heated metallic 
oxides, 91. 



INDEX. 



649 



Carbonic oxide, calorific value, 433. 

composition by volume, 

91. 
decomposition by heat, 91. 
formation in fires, 88. 
formed from steam, 89. 
identified, 88. 

loss of heat in furnaces pro- 
ducing, 433. 
metallurgic applications, 

88. 
poisonous properties, 89. 
preparation from carbonic 

acid, 88. 
preparation from ferrocy- 

anide of potassium, 90. 
preparation from oxalic acid, 

90. 
properties, 89. 
Carbonisation, 61. 
Carbonising fermentation, 69. 
Carbonyle, 437. 
Carbotriamine, 547. 
Carbovinate of potash, 528. 
Carburetted hydrogen, 98. 
Carmine, 608. 
Carmine lake, 608. 
Carminic acid, 608. 
Carnallite, 260. 
Carnelian, 113. 
Carraway, essential oil of, 476. 
Carre's freezing apparatus, 127. 
Carthamine, 603. 
Cartilage, 621. 
Case-hardening, 318. 
Caseine, 614. 

vegetable, 500, 614. 
CaSO^, calcium sulphate, 278. 
Cassia, essential oil, 482. 
Cassiterite, Sn0 2 , 347. 
Cast-iron, composition of,. 306. 
fusing-point, 308. 
grey, 307. 
malleable, 318. 
mottled, 307. 
phosphorus in, 307. 
silicon in, 119. 
specific gravity, 308. 
sulphur in, 307. 
varieties of, 307. 
white, 307. 
Castor oil, 583. 

cold -drawn, 583. 
Cast steel, 317. 
Catalan process, 320. 
Catalysis, 53, 530. 
Catechu, 595. 
Cat's eye, 113. 
Caustic alkali, 12. 

etymology of, 12. 
lunar, AgN0 3 , 382. 
potash, 258. 
soda, 265. 
Cd, cadmium, 289. 
Cedar -wood, essential oil, 477. 
Cedrene, 477. 
Cedriret, 470, 473. 
Celery, 506. 
(Jelestine, SrS0 4 , 276. 
Celluloid, 514. 
Cellulose, C 6 H 10 O 5 , 469. 



Cellulose, converted into sugar, 502. 

solvent for, 362. 
Cement for earthenware, 614. 

Keene's and Keating's, 279. 
Portland, 413. 
Roman, 413. 
Rust-joint, 193. 
Scott's, 413. 
Cementation process, 315. 

theory of, 316. 
Centrifugal sugar drainer, 505. 
Cerasine, 490. 
Cerine, 489. 
Cerite, 298. 
Cerium, Ce, 298. 

oxalate, 298. 
oxides, 298. 
Ceroleine, 585. 
Cerotene, 521. 
Cerotic acid, 520, 585. 
Cerotine, 585. 
Ceruse, 375. 

Cerylic alcohol, 518, 585. 
Cetine, 585. 
Cetyle, C ]6 H 33 , 584. 

series, 584. 
Cetylene, 521. 
Cetylic alcohol, 518. 

ether, 584. 
CH 3 , methyle, 436. 
CH^ marsh gas, 98. 
CH 4 0, methylic alcohol, 471. 
C 2 H 2 , acetylene, 92. 
C 2 H 4 , defiant gas, 95. 
C. 2 H 4 C1 2 , Dutch liquid, 96. 
C 2 H 5 , ethyle, 525. 
CoH 6 , ethane, 474. 
ClH 10 O, ether, 522. 
C 2 H 6 0, alcohol, 521. 
C 6 H 5 , phenyle, 465. 
C 6 H 6 , benzene, 458. 
C 6 H 7 N, aniline, 459. 
C 7 H 5 6, benzoyle, 481. 
C 10 H 8 , naphthalene, 467. 
Chalcedony, 113. 
Chalk, CaC0 3 , 277. 

decomposed by sodium, 88. 
in waters, 46. 
Chalybeate waters, 50, 321. 
Chameleon mineral, 329. 
Champagne, 515. 
Charbon roux, 417. 
Charcoal, absorption of gases by, 6Q. 

action of steam on, 89. 

animal, 67. 

as fuel, 69. 

ash, 417. 

burning, 65. 

combustion of, 68. 

decolorising properties, 67. 

deodorising properties, 6Q. 

for gunpowder, 417. 

oxidised by nitric acid, 137. 

preparation in the laboratory, 428. 

prepared at different tempera- 
tures, 417. 

properties of, 65. 

retort, 65. 

suffocation, 89. 

wood, 64. 
Charring by steam 418. 



650 



INDEX. 



Cheese, 613. 
Cheltenham water, 50. 
Chemical equivalent, definition, 12. 
Chemistry, definition, 1. 
Cheques, prepared paper for, 493. 
Che ssy lite, 363. 

ChevreuTs investigations, 572. 
Chili saltpetre, NaN0 3 , 414. 
Chill-casting, 308. 
Chimney, hot air, for lamps, 107. 
use of, in lamps, 107. 
ventilation by, 78. 
Chimneys on fire extinguished, 200. 
China moss, 490. 
Chinese wax, 584. 
Chinese white, 288. 
Chlonaphthalise. C 10 C1 8 , 169. 
Chloracetic acid,' HOHoClO.,, 566. 
Chloral, C 9 HC1 3 0, 555. 
Chloralum, 294. 
Chloranile, 598. 
Chloraniline, 550. 
Chlorate of baryta, 276. 

potash, KC10 3 , 163. 

action of heat on, 166. 
sulphuric acid 
on, 167. 
and sugar inflamed, 167. 
burnt in coal gas, 165. 
preparation, 163. 
preparation of oxygen 
from, 32. 
Chlorates, 164. 
Chlorethyl-sulphonic acid, 635. 

^sulphurous acid, 635. 
Chlorhydrine, 576. 

of glycol, 561. 
Chloric acid, 163. 
ether, 527. 
peroxide, C10 2 , 167. 
Chloride of aluminium and sodium, 294. 
ammonium, NH 4 C1, 269. 
calcium tube, 84. 
lime, 155. 

constitution of, 155. 
spontaneous decomposi- 
tion, 162. 
nitrogen, 171. 
nitrosyle, 172. 

preparation, 172. 
potassium, solubility of, 414. 
soda, 163. 
sodium, 260. 
sulphuryle, 201. 
thionyle, 201. 
Chlorine, CI, 147. 

action on ammonia, 153. 

hydrosulphuric acid, 196. 
leaves, 155. 
sal-ammoniac, 171. 
water, 152. 
and hydrogen, 150. 

exploded by sun- 
light, 150. 
exploded by spark, 
151. 
atomicity of, 248. 
bleaching by, 154. 
chemical relations of, 149. 
disinfecting properties, 156. 
etymology, 149. 



Chlorine, experiments with, 149. 
group of elements, 186. 
hydrate, 149. 
liquefied, 149. 
occurrence in nature, 147. 
oxides, 161. 

composition by volume, 168. 
general review, 168. 
oxidising action, 154. 
peroxide, 167. 
preparation, 148. 
properties, 149. 
taper in, 153. 
water, 149. 
Chlorite, 295. 
Chlorites, 168. 
Chlorobenzene, 458. 
Chlorocarbonic acid, COCl. 2 , 170. 

atomic constitution, 
249. 
Chlorochromic acid, 333. 
Chloroform, CHC1 3 , 553. 
Chloi-ophosphamide, 236. 
Chlorophyll, 602. 
Chloropicrine, CC1 3 (N0 2 ), 466. 
Chlorosulphuric acid, 201. 
Chlorous acid, 168. 
Chocolate, 600. 
Choke-damp, 77. 
Cholesterine, C^H^O, 635. 
Cholic acid, 635. 
Choline, 548. 
Choloidic acid, 635. 
Chondrine, 621. 
Chromates of lead, 332. 

of potash, 331. 
Chrome-alum, 332. 
Chrome-iron-ore, FeO.Cr 2 3 , 330. 
Chrome-yellow, PbCr0 4 , 332. 
Chromic acid, 331. 

action of hydrochloric acid 

on, 161. 
oxide, Cr 2 3 , 331. 
Chromium, Cr, 330. 

action on wate:*, 13. 
chlorides, 333. 
oxides, 331. 
oxychloride, 333. 
protoxide, 331. 
sesquichloride, 333. 
sesquioxide, Cr 2 3 , 332. 
sesquisulphide, 333. 
sulphate, 332. 
trifluoride, 333. 
Chrysaniline, 461. 
Chrysean, 446. 
Chrysene, 469. 
Chry sober yl, 290. 
Chrysocolla, 363. 
Churning, 612. 
Chyle, 636. 
Chyme, 635. 
Cigars, 602. 
Cinchona bark, 597. 
Cinch onine, 597. 

extraction of, 597. 
Cinder, 71. 
Cinder-iron, 305. 
Cinnabar, HgS, 391. 
Cinnameine, 477. 
Cinnamene, 478. 



INDEX. 



651 



Cinnamic acid, CgHgOg, 477. 

Cinnamon, essential oil of, 482. 

Cinnamyle, hydride, 482. 

Circulation of blood, chemistry of, 636. 

Cisterns, incrustations in, 47. 

Citric acid, H 3 C 6 H 5 7; 591. 

CI, chlorine, 147. 

Clarite, 245. 

Clark's process for softening water, 49. 

Clay, 291. 

Claying sugar, 505. 

Clay ironstone, average yield, 304. 

Clay ironstones, 300. 

C1 2 0, hypochlorous anhydride, 161. 

C1 2 3 , chlorous anhydride, 168. 

C1 2 4 , chloric peroxide, 167. 

Clot of blood, 615. 

Cloves, essential oil of, 476. 

CN, cyanogen, 443. 

CO, carbonic oxide, 88. 

C0 2 , carbonic acid gas, 72. 

Coal, 69. 

ash of, 71. 
Bathgate, 472. 
bituminous, 70. 

composition of, 433. 
Boghead, 472. 
brasses, 71. 
brown, 70. 
caking, 71. 
cannel, 71. 
combustion of, 70. 
composition of, 71. 
distillation of, 111, 452. 
formation of, 69. 
mines, fire-damp of, 98. 
products of combustion, 71 
distillation, 111. 
stone, 71. 
varieties of, 70. 
Welsh, 71. 
Coal gas, 111. 

composition of, 112. 
manufacture, 452. 

effect on chemistry, 452. 
purification, 453. 

removal of bisulphide of carbon 
from, 218. 
Coal naphtha, treatment of, 456. 
Coal tar, 455. 

distillation of, 456. 
dyes from, 460. 
Coarse copper, 357. 
Coarse-metal (copper), CuFeS 2 , 354. 
Cobalt, Co, 324. 

action on water, 13. 
arseniate, 237. 
bloom, Co 3 (As0 4 ) 2 , 237. 
chloride, 325. 

commercial oxide, preparation, 325. 
glance, CoAs 2 .CoS 2 , 324. 
oxides, 325. 
phosphate, 325. 
pyrites, Co 2 S 3 , 326. 
separation from nickel, 327. 
sulphides, 326. 
Cocaine, 540. 
Cocculus Indicus, 485. 
Cochineal, 608. 
Cochlearia, oil of, 486. 
Cocinic acid, 520. 



Cocoa, 600. 
Cocoa-nut oil, 574. 
Codeine, 540. 

extraction, 596 
Cod-liver oil, 584. 
Coerulignone, 473. 
Coffee, composition, 599. 

roasting, 599. 
Coil, induction, 10. 
Coin-bronze, 347 < 
Coke, 71. 

action of steam on, 89. 
composition, 433. 
Colcothar, 202, 322. 
Cold, greatest artificial, 141. 
saturated solution, 40. 
shortness in iron, 314. 
Collodion balloons made, 514. 

cotton, 513. 
Colophene, 475. 
Colophony, 476. 
Coloured fires, 165. 
Colouring-matters, animal, 608. 

vegetable, 602. 
Columbite, 352. 
Columbium, 352. 
Colza oil, 583. 
Combination by volume, 35. 

definition, 5. 
Combined carbon in cast-iron, 306, 308. 
Combining proportions, 5. 
Combustibles and supporters, reciprocity of, 

38, 106. 
Combustion, acetylene formed in, 92. 
definition, 24. 
formation of carbon dioxide in, 

72. 
furnace, 84. 
in air, definition, 24. 
in confined air, 76. 
in oxygen, 25. 
temperature of, 431. 
Common salt, NaCl, 260. 
Composition and constitution, 85. 
Compound and mixture, distinction, 60. 

definition, 3. 
Compressed gases, 38.. 
Concrete, 413. 
Condenser, Liebig's, 52. 
Condurrite, 237. 
Condy's disinfecting fluid, 329. 
Coniferine, 484. 
Coniine, 540. 

constitution, 545. 
Constitution of salts, 249. 
Converting furnace, 315. 
Converting vessel, Bessemer's, 313. 
Cooking. 620. 
Copal, 478. 
Copper, Cu, 352. 

aceto-arsenite, 241. 

acetylide, 93. 

action of nitric acid on, 137. 

on ammonia and air, 361. 
on water, 13. 
alloys of, 360. 
amalgam, 387. 
ammonio-sulphate, 363. 
Anglesea, 357. 
arsenite, 241. 
basic acetate, 566. 



652 



INDEX. 



Copper, "basic carbonates, 353, 363. 
phosphates, 363. 

best selected, 355. 

blistered, 355. 

chlorides, 363. 

cleaned, 361. 

detected in lead, 372. 

dry, 356. 

effect of impurties on, 357. 
phosphorus on, 358. 
sea- water on, 359. 

electric conductivity of, 358. 

electrotype, 358. 

emerald, 363. 

extraction in laboratory, 357. 

fusing-point, 358. 

glance, Cu 2 S, 352. 

hydrated oxide, 363. 

hydride, 233. 

Lake Superior, 352. 

lead in, 356. 

metallurgy of, 352. 

moss, 355. 

native, 352. 

ore, grey, 352. 
red, 353. 
variegated, 352. 

ores, 352. 

fusion for coarse metal, 354. 
white metal, 355. 
roasting, 353. 
treatment of, for silver, 379. 

overpoled, 356. 

oxide, CuO, 361. 

oxides, 361. 

oxy chloride, 359, 363. 

peacock, 352. 

pentasulphide, 365. 

phosphide, 234. 

poling or toughening, 356. 

precipitated, 94. 

properties of, 358. 

pyrites, CuFeS 2 , 352. 

quadrant oxide, 362. 

reduced by hydrogen, 38. 

refining, 355. 

rose, 357. 

sand, 352. 

separated from silver, 379. 

silicates, 363. 

smelting, composition of products 
from, 356. 

smelting, summary of, 353. 

smoke, 354. 

Spanish, 358. 

subchloride, Cu 2 Cl 2 , 363. 

suboxide, Cu.^O, 361. 

subsulphide, Cu 2 S, 364. 

sulphate, CuS0 4 , 362. 

action of heat on, 211. 
in bread, 501. 

sulphides, 364. 

tinning, 345, 359. 

tough- cake, 356. 

tough-pitch, 356. 

underpoled, 356. 

verdigris, 359. 

vessels for cooking, 359. 

with aluminium, 295. 
Copper-zinc couple, 14. 
Copperas, FeS0 4 , 323. 



Copperas, blue, 362. 

Coprolite, 222, 229. 

Coquimbite, 323. 

Coral, 277. 

Corallin, 466. 

Cork, 489. 

Corn-flour, 492. 

Corpse-light in coal-mines, 102. 

Corrosive sublimate, HgCl 2 , 388. 

antidote to, 389. 
antiseptic properties 
389. 
Corundum, 293. 
Cotton, 470. 

and wool, separation of, 622. 

dissolved by ammonio-cupric solu- 
tions, 362. 
Coumarine, 484. 
Cr, chromium, 330. 
Crackers, detonating, 451. 
Crampton's furnace, 314. 
Cream, 612. 

Cream of tartar, 257, 588. 
Creasote, 464, 466. 
Crenic acid, 633. 
Cress, essential oil of, 560. 
Cresole, 466. 

Cresylic acid, C 7 H 8 0, 466. 
Critical point, 81. 
Cr0 3 , chromic anhydrde, 331. 
Cr 2 3 , chromic oxide, 331. 
Crocus of antimony, 338. 
Crookes' discovery of thallium, 377. 
Croton-chloral, 555. 
Crotonic acid, 578. 

aldehyde, 555. 
Crow-fig, 600. 
Crucibles, 411. 

black lead, 63. 
graphite, 63. 
Cryohydrates, 43. 
Cryolite, 265. 
Crystalline lens, 616. 
Crystallisation, 40. 

Crystals from the leaden chambers, 204. 
CS 2 , carbon disulphide, 215. 
Cu, copper, 352. 
CuCl 2 , cupric chloride, 363. 
Cu 9 CL>, cuprous chloride, 363. 
Cudbe"ar, 606. 
Cumidine, 545. 
Cuminic acid, HC^E^Oo, 482. 

alcohol, 560. 
Cummin, essential oil, 482. 
Cumyle, 482. 

hydride, 482. 
Cumylene, 547. 

diamine, 547. 
CuO, oxide of copper, 361. 
CuO.S0 3 , sulphate of copper, 362. 
Cupel-furnace, 372. 
Cupellation on the large scale, 370. 
small scale, 372. 
Cupric acid, 362. 

chloride, CuCl 2 , 363. 

oxide, CuO, 361. 
Cupros-ethenyle oxide, 94. 
Cuprous acetylide, preparation, 93. 
chloride, Cu 2 Cl 2 , 363. 

ammoniacal, 364. 
solution, preparation, 93. 



INDEX. 



653 



Cuprous oxide, Cu 2 0, 361. 

Curarine, 601. 

Curcumine, 605. 

Curd of milk, 613. 

Curing animal matters, 639. 

Current, electric, 8. 

CuS, copper sulphide, 365. 

CuS0 4 , copper sulphate, 362. 

Cyamelide, 445. 

Cyanamide, 624. 

Cyanic acid, 445. 

ether, 624. 
Cyanide of phosphorus, 447. 

potassium, KCN, 444. 

commercial, 444. 
from blast furnaces, 
444. 
Cyanides of alcohol-radicals, 551. 
Cyanine, 603. 
Cyanite, 296. 
Cyanogen, CN, 443. 

chloi'ides, 447. 

compounds, 439. 

iodide, 446. 

preparation, 443. 

solution, metamorphosis of, 444. 
Cyanuric acid, 447, 623. 
Cy 6 Fe, ferrocyanogen, 440. 
Cylinder-charcoal, 65, 418. 
Cymole, C 10 H U , 477. 

Dadyle, 475. 

hydrochlorate, 475. 
Damaluric acid, 578. 
Dankes' furnace, 314. 
Daturine, 540. 
Davy-lamp, 100. 
Davyum, 400. 

Deacon's chlorine process, 149. 
Dead head, 346. 
Dead oil of coal-tar, 456. 
Decay, 72. 

Decolorising by charcoal, 67. 
Decomposing-cell, 8. 
Decomposition, definition, 6. 
Definition of acid salt, 251. 

alcohol, 517. 

atomic heat, 281. 

basic salt, 251. 

normal salt, 250. 

salt, 250. 
Deflagrating collar, 26. 

spoon, 26. 
Deflagration, 416. 
Dehydration, 42. 
Deliquescence, 43. 
Density, absolute, 421. 
apparent, 421. 
Deodorising by charcoal, 66. 
chlorine, 156. 
Dephlogisticated muriatic acid, 157. 
Derbyshire spar, 181. 
Desilverising lead, 369. 
Destructive distillation, definition, 64. 
Detonating tubes, 165, 586. 
Devitrification, 408. 
Dextrine, C 6 H 10 O 5 , 492. 
Dextrose, 503. 
Dextrotartaric acid, 590. 
Dhil mastic, 374. 
Diacetine, 565. 



Diacid diamines, 546. 
Di-allyle, 486. 
Dialysis, 114. 
Diamines, 546. 

aromatic, 547. 
Diamond, 61. 

ash of, 63. 

black, 63. 

combustion of, 62. 

dust, 63. 

glazier's, 63. 
Diamylamine, 543. 
Diaspore, 293. 
Diastase, 494. 
Diathermanous, 216. 
Diatomic elements, 247. 
Diazoamido-benzene, 463. 
Diazobenzene, 463. 

nitrate, 463. 
Dibenzyle, 469. 
Dichloracetic acid, 566. 
Dichloraniline, 550. 
Dichloranthracene, 604. 
Dichlorhydrine, 576. 
Didymium, Di, 297. 
Diet, regulation of, 637. 
Diethacetic acid, 570. 
ether, 570. 
Diethoxalic acid, 563. 
Diethyle, 525. 

Diethylamine, NH(C 2 H 5 ) 2 , 542. 
Diethyl-diethylene-diamine, 546. 
Diethylene-diamine, N 2 H 2 (C 2 H 4 ) 2 , 546. 

-diammonium, hydrate of, 546. 

-diethyl-tiiamine, 547. 

-trialcohol, 565. 

-triamine, 547. 

-tr-iammonium, trichloride, 548. 
Diethylzincamine, 553. 
Diffusibility of gases, definition, 18. 
law of, 18. 
measurement of, 19. 
rate of, 18. 
Diffusion-tube, 18. 
Digallic acid, 594. 
Digestion, 634. 

Dimethacetic (butyric) ether, 570. 
Dimethoxalic acid, 564. 
Dimethylamine, 543. 
Dimorphous, 62. 
Dinas fire-bricks, 411. 
Dinitraniline, 550. 
Dinitrobenzene, 139. 
Dinitro-diphenylamine, 544. 
Dicenanthylene-diaraylamiue, 558. 
Dioptase, 363. 
Dioxyanthraquinone, 604. 
Diphenylamine, 544. 
Diphenyl-benzoylamine, 544. 

-diethylene-diamine, 546. 
-guanidine, 547. 
-urea, 625. 
Diphenyle, (C 6 H 5 ) 2 , 462. 
Diphenyle oxide, 465. 
Diplatinamine, 396. 
Diplatosamine, 396. 

hydrate, 396. 
hydrochlorate, 396. 
sulphate, 396. 
Dipropargyle, 487. 
Discharge in calico printing, 156, 610. 



654 



INDEX. 



Disinfectant, MacDongall's, 465. 
Disinfecting by chloride of lime, 156. 
chlorine, 156. 
ferric chloride, 324. 
manganates, 329. 
Disinfecting fluid, Burnett's, 289. 

Condy's, 329. 
Disintegration of rocks, 80. 
Disodacetic ether, 570. 
Displacement, collection of gas by, 21. 
Dissociation of sal-ammoniac, 270. 

vermilion vapour, 391. 
Disthene, 296. 
Distillation, 51. 

definition of, 51. 
destructive, 64. 
dry, 64. 
fractional, 456. 
Distilled sulphur, 188. 

water, 51. 
Diterpene, 476. 

Dithionic (hyposulphuric) acid, 214. 
Ditoluylamine, 544. 
Divi-divi, 594. 
Dceglic acid, 578. 
Dolomite, MgCa.2C0 3 , 281. 
Dough, 499. 
Downcast shaft, 78. 
Dragon's blood, 478.. 
Dryers, 583. 
Drying gases, 38. 

in vacuo, 209. 
oils, 583. 

over oil of vitriol, 209. 
Dry rot, 502. 
Ductility of copper, 358. 
Dung as manure, 629. 
Dung- substitute, 242. 
Dust, 60. 
Dutch liquid, C 2 H 4 C1 2 , 96. 

action of chlorine on, 168. 
Dutch metal in chlorine, 150. 
Dyad elements, 247. 
Dyeing, 608. 
Dynamite, 580. 

Earthenware, 411. 
Earths, alkaline, 280. 

proper, 290. 
Ebonite, 488. 

Economico-furnace for lead-smelting, 368. 
Effervescence, 80. 
Efflorescence, 42. 
Eggs, 619. 
Egg shells, 73. 
Elaene, 521. 
Elaldehyde, 557. 
Elba iron ore, 300. 
Electrical amalgam, 386. 
Electrogilding, 404. 
Electrolysis, definition, 9. 

of hydrochloric acid, 160. 

of water, 4. 
Electro-negative elements, 9. 
Electroplating, 380. 
Electro-positive elements, 9. 
Element, definition, 3. 
Elements, non-metallic, general review, 246. 
Elemi resin, 478. 
Ellagic acid, 594. 
Embolite, 384. 



Emerald green, 241. 

Emery, 293. 

Emetics, 588. 

Emetine, 540. 

Empirical formulae, 85, 435. 

Empirical and rational formula?, 85, 435. 

Empyreumatic, 476. 

Emulsine, 480. 

Enamel glass, 409. 

Endosmose, 616. 

Eosine, 469. 

Epsom salts, 282. 

Equivalent, definition, 12. 

Erbium, 297. 

Erucic acid, 578. 

Erythric acid, 606. 

Erythrite, 606. 

Esculetine, 485. 

Esculine, 485. 

Essence of almonds, 480. 

turpentine, 474. 
Essential oils containing sulphur, 485. 

extraction of, 476. 
Ethal, C^Ti^O, 584. 
Ethalic acid, 584. 
Ethane, 474. 
Ethene dibromide, 96. 
Ethenyle-benzene, 95. 
Ether (C 2 H 5 ) 2 0, 522. 

chemical constitution, 531. 

decomposition by heat, 94. 

water-type view, 531. 
Etherification, continuous, 523. 

theory of, 529. 
Ethers, derivation from alcohols, 437. 
double, 531. 

perfuming and flavouring, 556. 
Ethylamine, NH 2 (C 2 H 5 ), 542. 
Ethylammonia or ethylia, 542. 
Ethyl- am yle ketone, 528. 
Ethylaniline, 544. 
Ethylate of aluminium, 530. 

potash, 530. 
Ethylate of soda, 530. 
zinc, 535. 
Ethyl-codyl-ammonium, hydrate of, 545. 
Ethyle, C 2 H 5 , 525. 
Ethyle-amyle, 525. 

-butyle, 525. 

carbonate, 528. 

cyanide, 532. 

glucose, 506. 

hydride, 535. 

hypothesis, 525. 

iodide, 524. 

kakodyle, 536; 

orthocarbonate, 528. 

peroxide, 568. 

sulphate, 528. 

sulphide, 531. 
Ethylene, C 2 H 4 , 95. 

diamine, N 2 H 4 (C 2 H 4 ), 546. 
dibromide, 546. 
hexethyl-diphosphonium, hydrate 

of, 549. 
oxide, 561. 
Ethylformiate of sodium, 568. 
Ethylic alcohol, 521. 

bromide, 524. 

chloride, 524. 

ether, 522. 



INDEX. 



655 



Ethylic iodide, 524. 
Ethylidene dichloride, 562. 
Ethyl-methyl-phenylamine, 544. 

-urea, 625. 
nicotyl-ammonium, hydrate of, 545. 
Ethylo-platammonium, hydrate of, 550. 

toluidine, 544. 
Ethyloxamide, 551. 
Ethylsulphuric acid, 528. 
Ethyl-urea, 625. 
Eucalyptus, 476. 
Euchlorine, 168. 
Eudiometer, Cavendish's, 34. 

etymology, 34. 

siphon, 36. 

Ure's, 36. 
Eudiometric analysis of air, 36. 

marsh gas, 110. 
Euodic acid, 519. 
Euphorbium, 487. 
Eupione, 473. 
Eupittonic acid, 473. 
Eupyrion matches, 167. 
Evernic acid, 606. 
Excretion, 636. 

Explosion of hydrogen and oxygen, 33. 
Explosions in coal-mines, 98. 

F, FLUORINE, 181. 

Fagotting, 312. 
Fallowing, 630. 
Fast colours, 608. 
Fats, 581. 

table of, 585. 
Fatty acid series, 519. 
Fatty acids, preparation, 574. 
Fey, ferrocyanogen, 440. 
Fe, iron, 299. 

Fe 2 Cl 6 , per chloride of iron, 323. 
Fe 4 Fcy 3 , Prussian blue, 441. 
Felspar, 295. 

potash-, 295. 
soda-, 295. 
Fennel, essential oil of, 482. 
FeO, protoxide of iron, 322. 
Fe 2 3 , peroxide of iron, 322. 
Fe 3 4 , magnetic oxide of iron, 322. 
FeO.S0 3 , protosulphate of iron, 323. 
Fermentation, 72. 

acetous, 498. 

alcoholic, 496. 

arrested by sulphurous acid, 

&c, 200. 
production of carbonic acid 

in, 72. 
viscous, 506. 
Ferric acid, 323. 

chloride, Fe B Cl 6 , 323. 

molecular formula, 324. 
oxide, Fe.>0 3 , 322. 
sulphate, "323. 
Ferricum, 324. 

Ferricyanogen (ferridcyanogen), Cy 6 Fe, 447. 
Ferrocyanates, 440. 
Ferrocyanic acid, 440. 
Ferrocyanide of potassium, K 4 Cy 6 Fe, 440. 

action of sulphu- 
ric acid on, 90. 
Ferrocyanogen, Cv 6 Fe, 440. 
Ferromanganese, 319. 
Ferrosoferric oxide, Fe 3 4 , 322. 



Ferrosum, 324. 
Ferrous oxide, FeO, 322. 

sulphate, FeS0 4 , 323. 
Ferruretted ehyazic acid, 440. 
FeS 2 , iron pyrites, 187. 
Fibrine,. blood-, 618. 

extracted from blood, 618. 
muscle-, 618. 
vegetable, 500. 
Fibroine, 622. 
Fibrous bar-iron, 314. 
Filtration, 67. 

Finery-cinder, 2FeO.Si0 2 , 309. 
Fire-bricks, 411. 
Fire-clay, 291. 
Fire-damp, 98. 

conditions of inflammation, 99. 
indicator, 99, 101. 
Fire, white, composition, 245. 
Fires, blue flame in, 88. 

coloured, 165. 
Fish oils, 573. 
shells, 73. 
Fixing photographic prints, 213. 
Flags, Yorkshire, 411. 
Flake-white, 337. 
Flame, analysis of by siphon, 106. 
blowpipe, 109. 
cause of luminosity in, 103. 
definition of, 102. 

effect of atmospheric pressure on, 107. 
oxygen on, 110. 
wire gauze on, 101. 
experimental study of, 104. 
extiuetion by gases, 75. 
extinguished by carbonic acid gas, 75. 
extinguished by good conductors, 100. 
gases in, 104. 
nature of, 102. 
oxidising, 109. 
reducing, 109. 
relation of fuel to, 108. 
separation of carbon in, 105. 
structure of, 102. 
supply of air to, 107. 
Flames, simple and compound, 103. 

smoky, 107. 
Flask, to make a three-necked, 106. 
Flesh, 619. 

composition of, 619. 
juice of, 619. 
Flint, 113. 
Flint and steel, 113. 
Flints dissolved, 267. 
Florence flask, 33. 
Floss-hole, 310. 

Flour, proximate analysis of, 499. 
Flowers bleached by sulphurous acid. 200. 
Fluoboric acid, 186. 
Fluocerine, 298. 
Fluocerite, 298. 
Fluoresceine, 469. 
Fluorescence, 485, 598. 
Fluoric acid, HF, 181. 
Fluoride of calcium, 181. 
silicon, 185. 
Fluorides, 184. 
Fluorine, F, 181. 

attempts to isolate, 183. 
Fluor-spar, CaF 2 , 181. 
I Flux, Baume's, 417. 



656 



INDEX. 



Flux in iron smelting, 303, 305. 
Food, effect of, upon respiration, 638. 
exportation, 638. 
plastic constituents of, 637. 
preservation of, 639. 
respiratory constituents of, 637. 
Forge-iron, 308. 
Fo-rmamide, 551. 
Formamidine, 443. 
Formic acid, HCHOo, 520, 568. 
Formonitrile, 551. 
Formulae, additive, 87. 

calculation of, 85. 
empirical and rational, 85, 435. 
substitutive, 87. 
Formylamine, hydriodate of, 443. 
Formyl-diphenyl-diamine, 546. 
Formyle, CH, 554. 

trichloride of, 554. 
Fouling of guns, 428. 
Foundry-iron, 308. 
Fousel-oil, 518. 
Fowler's solution, 241. 
Fractional distillation, 456. 
Frankincense, 487. 
Franklinite, ZnO.Fe 2 G 3 , 322. 
Free-stone, 411. 
Freezing-apparatus, 127. 

in red hot crucible, 199. 
mixtures, 128, 141, 270. 
of water, 52. 

with carbon disulphide, 217. 
French chalk, 281. 
Friction-tubes, 165. 

composition for, 165. 
Fructose, C 6 H 12 6 , 503. 
Fruit essences, 556. 
Fruits, ripening of, 632. 
Fuel, calculation of calorific intensity, 432. 
value, 430. 
chemistry of, 429. 
practical applications Of, 431. 
Fuels, composition of, 433. 

illuminating, composition of, 108. 
Fuller's earth, 291. 
Fulminic acid, 449. 
Fulminate of mercury, C 2 HgN 2 2 , 448. 

action of hydrochloric 

acid on, 451. 
preparation, 448. 
properties, 449. 
silver, 450. 
Fulminates, chemical constitution, 451. 

double, 451. 
Fulminating gold, 405. 

platinum, 395. 
silver, 382. 
Fumaric acid, 591. 
Fumigating with chlorine, 156. 

sulphurous acid, 201. 
Fuming sulphuric acid, 202. 
Fumitory, 591. 
Funnel-tube, 15. 
Fur in kettles, 45. 
Furfural, 569. 
Fur fur amide, 569. 
Furfurine, 569. 
Furfurol, C 5 H 4 2 , 569. 
Furnace, charcoal, 117. 

regenerative, 434. 
reverberatorv, 88. 



Furnace, Sefstrom's, 321. 
Furnaces, theory of, 430. 

waste of heat in, 433. 
Fused common salt, 157. 
Fusible alloy, 336. 
Fusing-points of fats, 585. 
Fusion, 114. 
Fustic, 603. 
Fuze, Abel's, 365. 

Armstrong percussion, 228. 

Gadolinite, 297. 

Galbanum, 487. 

Galena, PbS, 365. 

Gallic acid, 594. 

Gallium, 297. 

Gall-nuts, 592. 

Galvanic battery, 7. 

Galvanised iron, 284. 

Gamboge, 487. 

Gangue, 305. 

Garancine, 604. 

Garlic, essence, artificial production, 486. 

essential oil of, 485. 
Garnet, 295. 
Gas, air vitiated by, 77. 

-burner, Bunsen's rosette, 51. 
ring, 51. 
smokeless, 107. 
-carbon, 455. 
composition of, 112. 
-cylinder, 21. 
-holder, 90. 
valuation of, 97. 
-jar, 26. 

manufacture of, 452. 
springs, 98. 
Gaseous hydrocarbons, analysis of, 110. 
Gases, diffusion of, 18. 

expansion by heat, 426. 
in waters, 44. 
Gastric juice, 634. 
Gaultheria, oil of, 472. 
Gauze burner, 107. 
Gaylussite, 277. 
Gedge's metal, 360. 
Geic acid, 633. 
Gelatine, 621. 
Gelose, 490. 
German silver, 360. 
Germination, 494, 630. 
Germs of disease, 60. 
Geysers, 114. 
Gilding, 404. 

porcelain, 410. 
Gin, 516. 

Gl, glucinum, 289. " 
Glass, 407. 

bottle, 408. 

coloured, 408. 

composition of, 407. 

corrosion by hydrofluoric acid, 183. 

crown, 408. 

decolorised, 409. 

etched, 183. 

flint, 408. 

-gall, 408. 

manufacture of, 407. 

of antimony, 342. 

plate, 408. 

plate perforated, 204. 



INDEX. 



657 



Glass-pots, 411. 
silvered, 387. 
window, 407. 
Glauberite, 267. 
Glauber's salt. 211. 
Glaze for earthenware, 412. 
Glazier's diamond, 63. 
Globuline, 616. 
Glonoine, 579. 
Glucic acid, 506. 
Glucina, 289. 

separation from alumina, 290. 
Glucinum, Gl, 289. 
Glucose, C 6 H 12 6 , 501. 
artificial, 493. 
stearic, 579. 
Glucosides, 482. 
Gluco-tartaric acid, 579. 
Glue, 622. 
Gluten, 500. 

varieties of, 501. 
Glutine, 500. 
Glyceric acid, 563. 

alcohol, 577. 
aldehyde, 576. 
ether, 577. 
Glycerides, 576. 
Glycerine, C 3 H 8 3 , 577. 

converted into glycol, 576. 
extraction of, 575. 
properties, 577. 
soap, 573. 
triatomic, 564. 
Glyceryle, C 3 H 5 , 564. 
Glycocholic acid, 635. 
Glycocoll (glycocine), C 2 H 5 NOo, 622. 
Glycogen, 635. 
Glycol, C 2 H 6 2 , 561. 

acetobutyrate of, 565. 
aldehyde of, 562. 
binacetate of, 561. 
chlorhydrine of, 561. 
converted into alcohol, 564. 
monacetate of, 565. 
Glycolic acid, HCoH 3 3 , 563. 
Glycols, 561. 
Glycyrrhizine, 507. 
Glyoxal, 562. 
Gneiss, 296. 
Gold, Au. 400. 

and sodium, hyposulphite, 405. 

assay by cupellation, 403. 

coin, 402. 

crucible, 404. 

dissolved, 172. 

extracted from old silver, 401. 

extraction, 400. 

fulminating, 405. 

identification of, 137. 

in chlorine, 150. 

lace cleaned, 445. 

treatment of, 403. 
leaf, 404. 
oxides of, 404. 
physical properties, 403. 
protochloride, AuCl, 405. 
refining, 402. 

removal of mercury from, 386. 
ruby, 227, 404. 

separated from silver and copper, 209. 
standard, 402. 



Gold, standard, specific gravity of, 403. 
sulphides of, 406. 
testing, 403. 
thread, 404. 
trichloride, AuCl 3 , 404. 
Gongs, 347. 
Goulard's extract, 566. 
Gradational relations of elements. 186. 273, 

280. 
Grains, brewers', 495. 
Granite, 290. 

disintegration of, 290. 
Granitic rocks, 257. 
Granulated zinc, 14. 
Grape-husks, 515. 
juice, 515. 
sugar, C 6 H 14 07, 501. 

composition, 503. 
distinguished from cane-sugar, 
502. 
Grapes, colouring matter of, 603. 
Graphite, 63. 

ash of, 63. 
Graphite crucibles, 63. 

in cast-iron, 63, 307. 
uses of, 63. 
Grease removed from clothes, 463. 
Green, alkali, 549. 

arsenical, 241. 

borate of chromium, 332. 

Brunswick, 363. 

chrome, 332: 

colour of plants, 603. 

fire, composition for, 166. 

flame of barium, 276. 

boracic acid, 121. 
copper, 363. 
. thallium, 377. 
malachite, 363. 
mineral, 363. 
Rinman's, 325. 
salt of Magnus, 396. 
vitriol, 323. 
Grey copper ore, 352. 
Grey iron, 307. 

nickel ore, 326. 
powder, 386. 
Gristle, 621. 
Grotto del Cane, 74. 
Grough saltpetre, 413. 
Groups of non-metallic elements, 246. 
Grove's battery, 8. 
Guaiacum resin, 478. 
Guanidine, 547. 
Guanite, 283. 
Guano, 625, 629. 
Guelder rose, 571. 
Gum Arabic. 489. 
British, 492. 
Senegal, 490. 
tragacanth, 490. 
Gum-resins, 487. 
Gums, 489. 

Gun-cotton, C fl H 7 0.,(N0 3 ) 3 , 507. 
Abel's, 508.' ' 

compared with gunpowder, 512. 
composition, 509. 
equation of explosion, 510. 
in mining, 511. 

Karolyi's experiments on, 510. 
manufacture, 508. 

2 T 



658 



INDEX. 



Gun-cotton, objections to, 513. 

preparation, 507. 

products of explosion, 510. 

properties, 512. 

pulp, Abel's, 508. 

reconversion, 509. 
Gun-metal, 346. 
Gun-paper, 507. 
Gunpowder, 413. 

calculation of force, 424. 

collection of gases from, 423. 

composition, variations in, 423. 

dusting, 421. 

effect of pressure on explosion 
of, 428. 

equation of explosion, 424. 

examination of, 421. 

facing, 421. 

glazing, 421. 

granulating or corning, 420. 

heat of combustion, 425. 

hygroscopic character, 421. 

incorporation, 420. 

influence of size of grain, 427. 

manufacture, 419. 

mechanical effect, 426. 

preparation in the laboratory, 
428. 

pressing, 420. 

products of explosion, 424. 

slow combustion, 
• 426. 

properties, 421. 

smoke, 424. 

specific heat of products from, 
425. 

temperature of combustion, 426. 

volume of gas from, 426. 

white, 166. 
Gutta perch a, 489. 
Gypsum, 278. 

H, HYDROGEN, 14. 

Haemateine, 603. 
Hsematine, 616. 
Hcematite, brown, 300. 

red, Fe 2 3 , 300. 
Hoematosine, 617. 
Hsematoxyline, 603. 
Haemoglobine, 617. 
Hair, 622. 

Hair-dye, 215, 374, 382. 
Halogen, definition of, 186. 
Halogens, general review of, 186. 
Haloid salts, 186. 
Hammer-slag, 311. 
Hard metal, 346. 
Hardness, degrees of, 48. 

permanent, 48. 

temporary, 48. 
Hard water, 45. 
Hargreave's soda-process, 264. 
Harrogate water, 50. 
Hartshorn, spirit of, 127. 
Hausmannite, Mn 3 4 , 328. 
Hay, smell of, 484. 
HBr, hydrobromic acid, 174. 
HC1, hydrochloric acid, 157. 
HCy, hydrocyanic acid, 442. 
Heat and temperature, 431. 
atomic 280. 



Heat rays separated from light, 177, 216. 

relation to chemical attraction, 30. 

specific, 431. 
Heath's patent (steel), 317. 
Heating of hayricks, 69. 
Heat of combustion of hydrocarbons, 430. 
Heat-units, 429. 
Heavy-lead ore, Pb0 2 , 375. 

spar, BaS0 4 , 274. 
Hemihedral crystals, 590. 
Hemming's jet, 101. 
Hepatic waters, 50. 
Heptane, 474. 
Heptylene, 472. 
Hesperetine, 485. 
Hesperidine, 485. 
HF, hydrofluoric acid. 181. 
2HF.SiF 4 , hydrofluo-silicic acid, 185. 
Hg, mercury, 384. 
HgCl 2 , mercuric chloride, 388. 
HgCl, mercurous chloride, 389. 
Hg(N0 3 ) 2 , mercuric nitrate, 388. 
Bg 2 (N0 3 ) 2 , mercurous nitrate, 387. 
HgO, mercuric oxide, 387. 
Hg 2 0, mercurous oxide, 387. 
HgS, mercuric sulphide, 391. 
Hg 2 S, mercurous sulphide, 390. 
HI, hydriodic acid, 179. 
Hippuric acid, HC 9 H 8 N0 3 , 626. 

artificial formation, 627. 
extraction from cow's urine, 
626. 
H 2 0, water, 33. 
H 2 2 , hydric peroxide, 53. 
Hollway's process, 357. 
Homologous series, 438. 
Homology explained, 438, 578. 
Honey, 503. 
Hoofs, 622. 
Hopeite, 289. 
Hops, 496. 

essential oil of, 476. 
Hornblende, 296. 
Horn-lead, 376. 

-silver, 383. 
Horns, 622. 
Horse-chestnut bark, 485. 

-hair inflamed by nitric acid, 138. 
-radish, essential oil of, 485. 
Hot blast, theory of, 432. 
blast iron, 304. 
saturated solution, 40. 
H 2 S, hydrosulphuric acid, 194. 
H.,SiF 6 , hydrofluo-silicic acid, 185. 
H 2 S0 4 , sulphuric acid, 202. 
Humic acid. 633. 
Humus, 632. 
Hyacinth, 297. 
Hyseuic acid, 520. 
Hydrargyrum cum creta, 386. 
Hydrated bases, 43. 
Hydrate of lime, CaH.,Oo, 43. 
potash, KHO, 43. 
Hydrates, 43. 
Hydraulic cements, 413. 

main, 453. 
Hydric phosphides, 233. 

sulphides, 194. 
Hydrides of alcohol-radicals, 526. 
Hydriodate of potash, 180. 
Hydriodic acid, HI, 179. 



INDEX. 



659 



Hydriodic acid gas, preparation, 179. 

reducing properties, 179. 

solution, preparation, 179. 
ether, 524. 
Hydroboracite, 283. 
Hydrobromic acid, HBr, 174. 

Hydrocarbons, 92, 438. 

heat of combustion of, 430. 
turpentine-series, 476. 
Hydrocellulose, 502. 
Hydroohloric acid, HC1, 157. 

absorption by water, 158. 
action of heat on, 159. 
action on metallic oxides, 

160. 
action on metals, 159. 

nitric acid, 172. 
plants, 159. 
analysis of, 160. 
composition by volume, 

160. 
decomposed by the bat- 
tery, 160. 
from alkali-works, 158. 
gas, preparation of, 157. 
liquid, 158. 
properties, 157. 
pure, preparation of, 158. 
synthesis of, 150. 
valuation of, 158. 
yellow, 158. 
Hydrochloric ether, 524. 

gas, dry, preparation, 159. 
Hydrocyanic acid, HON, 442. 

anhydrous, 442. 
Liebig's test for, 446. 
synthesis, 95. 
ether, 532. 
Hydrocyan-rosaniline, 462. 
Hydroferricyanic acid, H 3 Cy B Fe, 447. 
Hydroferrocyanic acid, H 4 Cy 6 Fe, 442. 
Hydrofluoboric acid, 186. 
Hydrofluoric acid, HF, 181. 

action on metals, 183. 
silica, 183. 
Hydrofluo-silicic acid, 185. 

decomposed by heat, 
185. 
Hydrogen, H, 14. 

and arsenic, 242. 
carbon, 92. 
sulphur, 194. 
binoxide, 53. 
calorific intensity calculated, 432. 

value, 430. 
chemical properties, 20. 

relations, 40. 
displaced by sodium, 13. 
etymology of, 20. 
experiments with, 16. 
flame, 22. 

identification of, 9. 
peroxide, 53. 
persulphide, 198. 
phosphides, 233. 
physical properties, 16. . 
poured up through air, 16. 
preparation with iron, 14. 
zinc, 14. 
purification, 38. 



Hydrogen, selenietted, 220. 

sulphuretted, 194. 
•Hydrogenium, 40. 
Hydrokinone, 598. 
Hydronitroprussic acid, 447. 
Hydroselenic acid, H 2 Se, 220. 
Hydrosulphocarbonic acid, 217. 
Hydiosulphocyanic acid, HCyfcj, 446. 
Hydrosulphuric acid, H 2 S, 194. 

disposal of, 195. 

liquefied, 198. 

preparation, 194. 

production in waters. 
212. 

sohition of, 195. 

test for, 196. 

use in analysis, 197- 
ether, 531. 
Hydrosulphurous acid, 214. 
Hydrotelluric acid. H 2 Te, 221. 
Hydroxides, 43. 
Hydroxyle, 437. 
Hydroxyle theory of acids, 253. 
Hydroxylamine, NH 3 0, 138, 526. 
Hyoscyamine, 540. 
Hypobromous acid, 174. 
Hypochlorite of lime, 162. 
Hypochlorous acid, 161. 

action on sal-ammoniac, 172. 
Hypogeic acid, 578. 
Hyponitric acid, 145. 
Hyponitrites, 144. 
Hypophosphites, 232. 
Hypophosphoric acid, 232. 
Hypophosphorous acid, 232. 
Hyposulphates, 214. 
Hyposulphindigotic acid, 608. 
Hyposulphite of soda, Na 2 S 2 3 , 212. 
Hyposulphites, 213. 

constitution of, 214. 
Hyposulphuric (dithionic) acid, 214. 
Hyposulphurous acid, 212. 

I, iodine, 175. 

Ice, 52. 

Iceland spar, CaC0 3 , 277. 

Idrialene, 469. 

Illuminating gas from water, 89. 

Imides, 552. 

constitution of, 552. 
Imidogen, NH, 552. 
Incorporating mill, 420. 
Incrustation on charcoal, 109. 
Incrustations in boilers, 46. 
Indian fire, 245. 
Indian ink, 478. 
Indican, 607. 
Indifferent oxides, 29. 
Indigo, action of chlorine on, 154. 

artificial, 608. 

blue, C 16 H 10 N 2 O 2 , 607. 

copper, CuS, 365. 

red, 607. 

reduced, 607. 

vat, preparation, 607. 

white, 607. 
Indigotine, 608. 
Indium, 298. 

oxide, 298. 
Induction-coil, 10. 

tube, Siemens', 54. 



6G0 



INDEX. 



Ink, 592. 

blue, 441. 
from logwood, 603. 
red, 603. 

stains removed, 162. 
vanadium, 335. 
Inorganic substances, definition, 6. 
lnosite, C 6 H l2 6 , 620. 
Instantaneous light, 393. 
Introduction, 1. 
Intumescence, 267. 
lodammonium iodide, 180. 
Iodates, 178. 
Iodic acid, HI0 3 , 178. 
Iodide of ethyle, 524. 
nitrogen, 180. 
potassium, 180. 
silver, Agl, 384. 
Iodine, I, 175. 

action on ammonia, 180. 

potash, 176. 
and starch, 177. 
bromides, 180. 
chloride, IC1, 180. 
etymology of, 175. 
extraction from sea-weed, 175. 
identified, 176. 
oxides, 178. 
test for, 177. 
tincture of, 177. 
trichloride, IC1 3 , 180. 
Iodised starch paper, 55. 
Iodoform, 554. 
Iridium, Ir, 399. 

ammoniochloride, 399. 
black, 399. 
chlorides, 399. 
oxides, 399. 
Iron, Fe, 299. 

action of acids on, 321 . 

air of towns on, 284. 
hydrochloric acid on, 160. 
on water, 13. 
amalgam, 387. 
and carbon, 306. 
and oxygen, 28. 

and potassium, ferrocyanide, 441. 
atomic weight, 324, 
bar-, 312. 

basic persulphate, 202. 
bisulphide, 301. 
black oxide, 322. 
bright, 307. 
carbonate, 300. 
cast, 306. 

chemical properties, 321. 
chlorides, 323. 
cold short, 314. 
diatomic, 324. 

extraction in the laboratory, 321. 
ferricyanide, 446. 
fibre in, 314. 
galvanised, 284. 
glance, 300. 
grey, 307. 

group of metals, general review, 334. 
in blood, 617. 
in zinc, 287. 
iodide, 181. 

magnetic oxide, Fe 3 4 , 322. 
metallurgy, 301. 



Iron, mottled, 307. 

-mould, 321, 586. 

occurrence in nature, 299. 

of antiquity, 319. 

ores, 300. 

British, composition, 300. 
calcining or roasting, 302. 

oxides, 322. 

passive state of, 321. 

perchloride, Fe 2 Cl 6 , o23. 

peroxide, Fe 2 3 , 322. 

persulphate, Fe 2 3S0 4 , 323. 

phosphates, 323. 

phosphorus in, 314. 

plates cleansed, 345. 

proto-chloride, 323. 

proto-sesquioxide, 322. 

proto-sulphate, 323. 

uses, 323. 

protoxide, FeO, 29, 322. 

prussiate, 440. 

pure, preparation of, 321. 

purification, 309. 

pyrites, FeS 2 , 301. 

pyrophoric, 29, 91. 

red oxide, 322. 

red short, 314. 

refining, 309. 

rust, ammonia in, 132. 

rusting of, 321. 

sand, 301. 

scales, 311. 

scurf, 411. 

separation from manganese, 330. 

sesquichloride, 323. 

sesquiferrocyanide, 441. 

sesqui-iodide, 181. 

sesquioxide, 29. 

sesquisulphate, 323. 

smelting, English method, 302. 

specular, 300. 

steely, 321. 

sulphate, action of heat on, 211. 

nitric acid on, 142. 

sulphide, preparation, 194. 

sulphuret, 194. 

sulphur in, 314. 

tincture of, 324. 

tinned, 345. 

triatomic, 324. 

useful properties of, 301. 

variation in strength of, 314. 

white, 307. 

wire, composition, 312. 

works of the Pyrenees, 320. 

wrought or bar, composition, 314. 
direct extraction, 319. 
manufacture, 308. 
Iserine, 350. 
Isethionic acid, 635. 

chloride, 635. 
Isinglass, 622. 
Iso-alcohols, 517. 
Isocumole, 454. 
Isodimorphism, 339. 

of antimonious oxide and 
arsenious oxide, 246. 
Isologous series, 438. 
Isomeric, 439. 
Isomerism, 439. 

explanation of, 439. 



INDEX. 



661 



Isomorphism, 363. 
Isoprene, 488. 
Isopurpurates, 466. 
Isotartaric acid, 588. 
Isoterebenthene, 475. 
Ivory, artificial, 514. 
Ivory-black, 67. 

Japan, 473. 

Jasper, 113. 

Jatrophine, 492. 

Jellies, fruit, 632. 

Jelly, 621. 

Jet, 71. 

Jet for burning gases, 22. 

Jeweller's rouge, 322. 

Juice of sugar-cane, 503. 

Juniper, essential oil of, 476. 

K, potassium, 257. 
Kainite, 283. 
Kakodyle, C. 2 H 6 As, 532. 

chemical constitution of, 532. 

chloride, 532. 

cyanide, 533. 

oxide, 532. 

series, 533. 
Kakodylic acid, 533. 
Kaolin, 291. 
Kapnomor, 473. 
KC1, potassium chloride, 260. 
2KC],PtCl 4 , potassium platino-chloride, 395. 
KC10 3 , „ chlorate, 163. 

K 2 C0 3 , „ carbonate, 257. 

KCy, „ cyanide, 444 

KCyO, ,, cyanate, 445. 

KCyS, ,, sulphocyanide, 445. 

Kekule's chain, 459. 
Kelp, 175. 
Kentledge, 305. 
Kermes mineral, 342. 
Kernel roasting, 364. 
Kerosene, 474. 

shale, 472. 
Kerosoline, 474. 
Ketones, 437, 558. 

K 4 Fcy, potassium ferrocyanide, 440. 
K 3 Fdcy, potassium ferricyanide, 447. 
KHG0 3 , bicarbonate of potash, 260. 
KHO, caustic potash, 258. 
KHSO4, bisulphate of potash, 211. 
KI, potassium iodide, 180. 
Kid, 593. 
Kieselguhr, 580. 
Kieserite, 283. 
King's yellow, 245. 
Kinic acid, 598. 
Kino, 595. 

Kinone, C 6 H 4 2 , 598. 
Kirschwasser, 516. 
Kish, 63. 
Klumene, 92. 

KMn0 4? potassium permanganate, 329. 
KNO3, saltpetre or nitre, 413. 
K 2 0, dipotassium oxide, 259. 
K 2 O.Cr0 3 , chromate of potash, 331. 
K 9 0.2Cr0 3 , bichromate of potash, 331. 
Kola nut, 598. 

K 2 O.Sb 2 5 , antimoniate of potash, 339. 
Koumiss, 613. 
Kreasote, 464, 466. 



Kreatine, C 4 H 9 N 3 2 , 619. 

extraction from flesh, 619. 
Kreatinine, C 4 H 7 N 3 0, 620. 
Kresole, 466. 
Kresyle, 466. 

Kresylic acid, C 7 H 8 0, 466. 
Krupp's steel, 319. 
Kryolite, Na 3 AlF 6 , 265. 
K 2 S, potassium sulphide, 422. 
Kupfemickel, NiAs, 326. 
Kyanising wood, 633. 
Kyanite, 296. 

Lac, 478, 608. 
seed, 478. 
shell, 478. 
stick, 478. 
Lacquer, 478. 
Lacquering, 360. 
Lactarine, 614. 
Lactic acid, HC 3 H 5 3 , 486, 563, 612. 

converted into butyric, 569. 

propionic, 613. 
preparation, 612. 

anhydride, 613. 

fermentation, 612. 

series of acids, 563. 
Lactide, 613. 
Lactine, C 12 H 24 12 , 614. 
Lactometer, 615. 
Laevotartaric acid, 590. 
Lagunes, boracic, 120. 
Lakes alumina, 608. 
Lamp, action explained, 104. 

-black, 64. 

without flame, 393. 
Lanarkite, 376. 
Lanthanium, La, 297. 
Lapis Lazuli, 296. 
Lard, 584. 
Laughing gas, 140. 
Laurel water, 442, 481. 
Laurent's doctrine of substitution, 467. 

nomenclature, 467. 
Laurie acid, 519. 

alcohol, 518. 
Laurite, 398. 
Lava, 296. 

Law of multiple proportions, 146. 
Lead, Pb, 365. 

acetate, Pb(C 2 H 3 2 ) 2 , 565. 

action of acids on, 373. 

sulphuric acid on, 207, 373. 
on water, 13, 50. 

amalgam, 387. 

argentiferous, 369. 

basic carbonate, 375. 
chromate, 332. 

binoxide, 375. 

calcining, 368. 

carbonate, native, 376. 

chloride, PbCl 2 , 376. 

chlorobromide, 377. 

chlorosulphide, 377. 

chromate, PbO.Cr0 3 , 332. 

dichromate, 332. 

extraction in the laboratory, 372. 

fusing-point of, 365. 

-glazed earthenware, 374, 411. 

hard, 368. 

hydrated oxide, 374. 



662 



INDEX. 



Lead, hyposulphite, 214. 

improving process, 368. 

in cider, &c, 373. 

in water, 50. 

iodide, Pbl 2 , 178, 377. 

malate, 591. 

metailurgic chemistry, 366. 

molybdate, 334. 

ores, 365. 

oxide, use of, in glass, 407. 

oxides, 373. 

oxy chloride, 376. 

peroxide, Pb0. 27 375. 

phosphate, 376. 

plaster, 577. 

protoxide, PhO, 373. 

pyrophorus, 373. 

selenide, 377. 

smelting, 366. 

Spanish, 368. 

specific gravity, 365. 

sugar of, 565. 

sulphate, PbS0 4 , 366, 376. 

sulphides, 377. 

tartrate, preparation, 373. 

test for, in water, 50. 

tribasic acetate, 565. 

uses, 365. 

vanadiate, 335. 
Lead-vitriol, PbS0 4 , 376. 
Leaden cisterns, danger, 50. 

coffins, corrosion, 373. 
Leadhillite, 376. 
Leather, 593. 
Leaven, 501. 

Leaves, formation of, 631. 
Lecanoric acid, 606. 
Leeks, essential oil of, 485. 
Legumine, 614. 
Lemery's volcano, 193. 
Lemons, essential oil of, 476. 
Lepargylic acid, 582. 
Lepidolite, 271. 
Leucaniline, 461. 

triphenylic, 462. 
Leucic acid, HC 6 H n 3 , 563. 
Leucine, C 6 H 13 N0 2 , 622. 
Leucone, 119, 171. 
Levulose, 503. 
Li, lithium, 271. 
Libethenite, 363. 

Lichens, colouring matter from, 606. 
Liebig's condenser, 52. 

extract, 620. 
Life, its extremes meet, 640. 
Light, action on chloride of silver, 213. 

rays separated from heat, 177, 216. 
Light carburetted hydrogen, 98. 

oil of coal-tar, 456. 
Lign aloes, essence of, 477. 
Lignine, 469. 
Lignite, 70. 

composition, 71, 433. 
Ligroine, 474. 
Lime, CaO, 277. 

action on soils, 630. 

agricultural uses, 630. 

bimalate, 591. 

burning, 277. 

carbonate, CaO.C0 2 , 277. 
in waters, 46. 



Lime, fat, 278. 

hydrate, CaO.H 2 0, 278. 

hypochlorite, 162. 

hyposulphite, 212. 

kilns, 278. 

-light, 39. 

lactate, 612. 

overburnt, 278. 

oxalate, CaC^ 587. 

platinate, 394. 

poor, 278. 

purifier, 454. 

-stone, CaO.COo, 277. 

sulphate, CaO,S0 3 , 278. 

superphosphate, 222. 

test for, 587. 

water, 278. 
Linen, 470. 
Linoleic acid, 583. 
Linseed, 490. 

oil, 583. 

boiled, 583. 
Lipic acid, 582. 

Liquation of argentiferous copper, 379. 
Liquor ammoniae, 124. 

chlori, 149. 

iodi, 177. 

sanguinis, composition, 618. 
Liquorice root, 507. 
Litharge, PbO, 374. 
Lithia, 271. 

carbonate, 271. 
-mica, 271. 
phosphate, 271. 
Lithic (uric) acid, 625. 
Lithium, Li, 271. 

blowpipe test for, 271. 
Litmus, 606. 

commercial, 606. 
Loadstone, Fe 3 4 , 29, 301. 
Loam, 291. 
Logwood, 603. 

Looking-glasses silvered, 386. 
Lucifer matches, 165, 227. 

tipped with sulphur, 227. 
Lugol's solution, 177. 
Luminosity of flames, 103. 
Lunar caustic, 382. 
Lupuline, 496. 
Luteoline, 603. 
Luting for crucibles, 285. 

iron joints, 193. 
Lycopodium, 102. 

Madder, 603. 
Magenta, 460. 
Magic lantern, oil for, 477. 
Magnesia, MgO, 283. 

calcined, 283. 

citrate, 591. 

hydrate, 283. 

hydraulic, 283. 

medicinal, 283. 

silicates, 283. 

sulphate, MgO.S0 3 , 282. 
Magnesian limestone, 281. 

for building, 412. 
Magnesite, 281. 
Magnesium, Mg, 281. 

action on water, 13. 
ammoniophosphate, 283. 



INDEX. 



663 



Magnesium arsenite, 240. 

borate, 283. 

carbonate, 283. 

chloride, 118, 283. 

extraction from sea- 
water, 261. 

extraction, 281. 

fluoride, 184. 

hydrate, 283. 

nitride, 282. 

phosphate, 283. 

properties, 281. 

silicates, 283. 

silicide, 118. 

sulphate, MgS0 4 , 282. 
Magnet-fuze composition, 365. 
Magnetic iron ore, Fe 3 4 , 322. 
Magnus' green salt, 396. 
Malachite, 353. 
Malaeic acid, 591. 
Malamide, 592. 
Malic acid, H 2 C 4 H 4 5 , 591. 

converted into acetic, 592. 

succinic, 592. 
extracted from rhubarb, 591. 
formed from succinic, 590. 
tartaric, 589. 
Malleability of copper, 358. 
Malleable cast-iron, 318. 
Malonic acid, 582. 
Malt dust, 495. 

high dried, 498. 
Malting, 494. 
Maltose, 503. 
Manganate of potash, 328. 

soda for preparing oxygen, 31. 
Manganese, Mn, 327. 

action on water, 13. 

alum, 328. 

binoxide, action of sulphuric 
acid on, 211. 

Hack, 327. 

carbonate, 328. 

chlorides, 330. 

dioxide Mn0 2 , 327. 

hydrated peroxide, 327. 

oxides, 327. 

peroxide, 327. 

protoxide, MnO, 328. 

recovery from chlorine residues, 
330. 

red oxide, 328. 

separation from iron, 330. 

sesquioxide, Mn 2 3 , 328. 

spar, MnC0 3 , 328. 

sulphate, MnS0 4 , 327. 

test for, 328. , 
Manganic acid, 328. 
Manganite, Mn 2 3 .H 2 0, 328. 
Manna, 506. 
Mannitane, 579. 
Mannite, C 6 H 14 6 , 506. 
glycerides, 579. 
glycerine, 579. 
stearine, 579. 
Mantle of flame, 106. 
Manures, 629. 
Manuring, 628. 
Maraschino, 516. 
Marble, 279. 
Marcasite, 301. 



Margaric acid, 520, 582. 
Margarine, 582. 
Marine glue, 488. 
Marking-ink, 382. 
Marl, 291. 
Marsh gas, CH 4 , 98. 

and chlorine, 154. 
composition by volume, 110. 
eudiometric analysis, 110. 
identified, 98. 
preparation, 98. 
series, C n H 2n + 2 , 526. 
Marsh-mallow, 490. 
Marsh's test for arsenic, 242. 
Mascagnine, 268. 
Massicot, PbO, 374. 
Matches, 165. 

eupyrion, 167. 
lucifer, 227. 
safety, 227. 
silent, 227. 
Vesta, 167. 

without phosphorus, 228. 
Matt, 354. 

Matter, definition of, 1. 
Mauve, 460. 
Mauveine, 460. 
Meadow-sweet, oil of, 482. 
Meal powder, 420. 
Meconic acid, H 3 C 7 H0 7 , 597. 
Meerschaum, 281. 
Melaniline, 547. 
Melissene, 521. 
Melissic acid, 520. 

alcohol, 518. 
Melissine, 585. 
Menaccanite, 350. 
Mendelejeffs-law, 256. 
Mendipite, PbCl 2 .2PbO, 377. 
Menthene, 477. 
Menthole, 477, 
Mercaptan, 531. 
Mercaptide of mercury, 531. 
Merchant bar iron, 312. 
Mercuramine, 387. 
Mercuric ethide, Hg(C 2 H 5 ) 2 , 537. 
fulminate, 448. 
iodide, Hgl 2 , 390. 
methide, 537. 
nitrate, Hs(N0 3 )„ 388. 
sulphate, HgS0 4 f 388. 
Mercurous chloride, HgCl, 389. 
iodide, Hgl, 390. 
nitrate, Hg 2 (N0 3 )o, 388. 
sulphate, Hg 2 O.S0 3 , 388. 
Mercury, Hg, 384. 

action of hydrosulphuric acid on 

196. 
amido-chloride, 389. 
ammoniated oxide, 387. 
bichloride or perchloride, 388. 
black oxide, Hg.,0, 387. 
chloride, HgCl 2 f 388. 
chlorosulphide, 391. 
cyanide, Hg(CN). 2 , 442. 
extraction from its ores, 384. 
frozen by liquid sulphurous acid, 

199. 
fulminate, HgC 2 N 2 0o, 448. 
iodide, 390. 
metallurgy of, 384. 



664 



INDEX. 



Mercury, nitrate, Hg(N0 3 ). 2 , 388. 
nitric oxide of, 387. 
nitride, 387. 
oxides, 387. 

protochloride, HgCl, 389. 
protonitrate, Hg 2 (N0 3 ) 2 , 388. 
prussiate, 440. 
red oxide, HgO, 387. 
stains removed from gold, 387- 
subsulphide, 390. 
sulphate, 388. 
sulphide, 390. 
uses of, 386. 
volatility of, 386. 
yellow oxide, HgO. 387. 
Metacetone, 559. 
Metacetonic (propylic) acid, 519. 
Metal, definition, 29. 
Metalamides, 553. 
Metaldehyde, 557. 
Metallic oxides, action of hydrochloric acid 

on, 160. 
Metallurgy of copper, 352. 
iron, 301. 
lead, 342. 
tin, 342. 
zinc, 285, 
Metals, action of hydrochloric acid on, 159. 
hydrosulphuric acid on, 

196. 
sulphuric acid on, 209. 
on water, 12. 
burnt in sulphur vapour, 193. 
chemistry of, 254. 
classification of, 254. 
iron group, general review, 334. 
noble, 13. 

of the alkalies, general review, 273. 
of the alkaline earths, 280. 
platinum group, 399. 
relations to oxygen, 27. 
Metal-slag (copper), 355. 
Metameric, 439. 
Metantimonic acid, 340. 
Metaphosphates, 232. 
Metaphosphoric acid, HP0 3 , 232. 
Metastannic acid, 348. 
Metastyrole, 478. 
Metatartaric acid, 588. 
Metaterebenthene, 475. 
Meteoric iron, 299. 
Methylamine, 543, 548. 
Methylaniline, 544. 
Methylated spirits, 479. 
Methyle, CH 3 , 436. 

-caproyle, 525. 

chloride, 548. 

-phenylamine, 544. 

prepared from acetic anhydride, 

567. 
salicylate, 472. 
series, 436. 
-theobromine, 600. 
toluene, 459. 
Methylethylamine, 543. 
Methyl-amylo-phenylium, hydrate, 544. 
Methylethylaniline, 544. 
Methyl-ethyl-amylo-phenyl-ammonium, hy- 
drate, 544. 
Methylethylic ether, 531. 
Methyl-hexyl ketone, 528. 



Methylmorphylammonium, hydrate, 545. 
Methylation, 438. 
Methylic acetate, 471. 

alcohol, CH 4 0, 471, 517. 
formiate, 471. 
hydrate, 471. 
Methyluric acid, 626. 
Mg, magnesium, 281. 
MgO, magnesia, 283. 
MgO.S0 3 , sulphate of magnesia, 282. 
Mica, 290. 

Microcosmic salt, 232. 
Mildew, 60. 
Milk, 612. 

adulteration, 615. 
coagulation of, 612. 
composition of, 615. 
Mill-cake, 420. 

furnace, 312. 
Millstone grit, 411. 
Mimotannic acid, 595. 
Mine iron, 305. 
Mineral cotton, 306. 
green, 363. 
silicates, 295. 
waters, 50. 
yellow, 377. 
Mines, ventilation, 78. 
Minium, Pb 3 4 , 374. 
Mirbane, essence of, 139. 
Mirrors, manufacture, 386. 
Mispickel, FeS 2 , FeAS 2 , 236. 
Mixture and compound, distinction, 60. 
Mn, manganese, 327. 
Mn0 2 , peroxide of manganese, 327. 
Moire metallique, 347. 
Molasses, 503. 
Molecular compounds, 270. 
formula, 435. 
weight, 3, 436. 
Molecule, definition, 1, 2. 

of a base determined, 132. 
of an acid determined, 85. 
of water, 2. 
Molecules, 1, 2. 
Molybdate of lead, 334. 
Molybdena, MoS 9 , 334. 
Molybdenum, Mo, 334. 

bisulphide, 334. 
blue oxide, 334. 
chlorides, 334. 
metallic, 334. 
oxides, 334. 
Molybdenum sulphides, 334. 
Molybdic acid, Mo0 3 , 334. 

dialysed, 334. 
ochre, 335. " 
Monacetine, 565. 
Mona copper, 357. 
Monad elements, 247. 
Monamines, 545. 
Monatomic elements, 247. 
Monkshood, 591. 

Monobasic acids, constitution of, 250. 
Monophosphamide, 236. 
Monostearine, 576. 
Mordants, 609. 
Moringic acid, 578. 
Moritannic acid, 603. 
Morocco leather, 593. 
Morphine, C 17 H 19 N0 3 , 596. 



INDEX. 



665 



Morphine, characters of, 596. 

extraction, 596. 

hydrochlorate, 597. 
Mortar for building, 412. 
Mould, 60. 
Mosaic gold, 350. 
Mountain ash berries, 591. 
Mucic acid, 490. 
Mucilage, 490. 
Mucus, 623. 
Muffle, 372. 

Mulberry calculus, 585. 
Multiple proportions, law of, 146. 
Mundic, FeS 2 , 301. 
Muntz metal, 360. 
Murexide, 626. 
Muriate of morphia, 597. 
Muriatic acid, 158. 
Muscle formed from food, 634. 
Mushrooms, 506. 
Muslin, uninflammable, 268, 351. 
Mustard, essential oil of, 485. 

artificial production, 486. 
Myosine, 620. 
Myricine, 585. 
Myristic acid, 520. 
Myronic acid, 485. 
Myrosine, 485. 
Myrrh, 487. 

N, NITROGEN, 122. 

Na, sodium, 260. 
NaCl, common salt, 260. 
Nails, 622. 

Na o 0, disodium oxide, 265. 
Na 2 O.B 2 3 , borax, 119, 266. ' 
Na 2 C0 3 , sodium carbonate, 262. 
NaHO, caustic soda, 265. 
NaHC0 3 , bicarbonate of soda, 264. 
Na 2 HP0 4 , sodium phosphate, 267. 
NaN0 3 , „ nitrate, 414. 

Na 2 S0 4 , ,, sulphate, 267. 

Na 2 S 2 3 , ,, hyposulphite, 212. 

Naphtha, coal, 455. 

wood, 471. 
Naphthalic acid, 468. 
Naphthalene, C 10 Hg, 467. 

chlorides, 468. 

chlorine substitution-products 
from, 467. 

nitro - substitution products 
from, 468. 
Naphthalising, 105. 
Naples yellow, 377. 
Narcotine, 540. 

extraction, 597. 
Nardic acid, 520. 
Nasturtium, oil of, 560. 
Negative pole, 8. 
Nessler's test for ammonia, 390. 
Nettles, acid of, 568. 
Neurine, 548. 
Neutralisation, 12. 
Neutrality of constitution, 250. 
NH 3 , ammonia, 123. 
NH 4 , ammonium, 130. 
NH 4 C1, ammonium chloride or sal-ammoniac, 

124. 
2NH 4 Cl,PtCl 4 , ammonio-chloride of plati- 
num, 395. 
NH 3 ,H(J1, sal-ammoniac, 124. 



(NH 4 ) 2 C0 3 , ammonium carbonate, 268. 
(NH 4 ) 2 C 2 4 , „ oxalate, 587. 

(NH 4 ) 2 S0 4 , „ sulphate, 268. 

(NH 4 ),S, „ sulphide, 270. 

Ni, nickel, 326. 
Nickel,- Ni, 326. 

action on water, 13. 
arsenical, NiAs 2 , 326. 
arsenio-sulphide, 326. 
glance, NiAs 2 NiS 2 , 326. 
oxides, 326. 
sulphate, 326. 
sulphides, 327. 
Nicotine, C 10 H 14 N 2 , 601. 
extraction, 601. 
properties, 601. 
Nil album, 285. 
Niobic acid, 352. 
Niobium, Nb, 352. 
Nipper-tap, 152. 
Nitraniline, 550. 

Nitrate of potash, action of heat on, 140. 
solubility, 414. 
silver prepared from standard sil- 
ver, 382. 
soda, solubility, 414. 
Nitrates, composition, 140. 

decomposition by heat, 140. 
formation in nature, 133. 
oxidising properties, 139. 
Nitre, KN0 3 , 413. 

action on carbon, 416. 
artificial production, 414. 
cubic, 414. 
examination of, 416. 
-heaps, 414. 
properties, 416. 

purified in the laboratory, 429. 
refining, 415. 

relation to combustion, 416. 
Nitric acid, HN0 3 , 134. 

action on benzene, 139. 
charcoal, 137. 
hydrochloric acid, 172. 
indigo, 136. 
metals, 137. 
organic substances, 
■ 138. 

phosphorus, 137. 
sulphurous acid, 205. 
turpentine, 138. 
anhydrous, 139. 
cause of colour, 136. 
decomposed by heat, 136. 
light, 136. 
distillation of, 136. 
formed from air, 134. 

ammonia, 132. 
from batteries, 145. 
fuming, 136. 

oxidising properties, 137. 
preparation on the large scale, 

135. 
preparation on a small scale, 135. 
properties, 136. 
strongest, preparation, 135. 
test of strength, 136. 
anhydride, 139. 
ether, 527. 
oxide, NO, 141. 

analysis of air by, 142. 



666 



INDEX. 



Nitric oxide, behaviour with hydrogen, 143. 
identified, 141. 
pure, preparation, 142. 
with carbon disulphide, 152. 
peroxide, N0 2 , 145. 

composition by volume, 
147. 
Nitrification, theory of, 133. 
Nitriles, 551. 
Nitrites, 144. 
Nitrobenzoic acid, 627. 
Nitrobenzene, C 6 H 5 (N0 2 ), 459. 
preparation, 139. 
Nitro-ethane, 527. 
Nitrogen, N, 122. 

atomicity of, 246. 
binoxide, 141. 
bromide, 174. 
bulbs, 131. 

chemical relations, 123. 
chloride, 171. 

preparation, 171. 
circulation in nature, 124. 
determination, 131. 
etymology, 59. 
function in air, 60. 
group of elements, 246. 
identification of, 123. 
iodide, 180. 
oxides, 146. 

general review, 146. 
peroxide, 145. 
preparation, 123. 
properties, 59. 
protoxide, 140. 
sulphide, 218. 
Nitrogenised bodies identified, 68. 
Nitroglycerine, 579. 

use in blasting, 580. 
Nitrohippuric acid, 627. 
Nitromagnite, 581. 
Nitromannite, 514. 
Nitromuriatic acid, 172. 
Nitrophenisic acid, 465. 
Nitroprussides, 447. 
Nitrosubstitution products, 139. 
Nitrosyle chloride, 172. 
sulphate, 172. 
Nitrotoluole, 464. 
Nitrous acid, 143. 

action on hydrosulphuric acid, 

196. 
action on organic substances, 

144. 
commercial, 145. 
composition by volume, 146. 
formed from ammonia, 132. 
oxidising and reducing power, 
146. 
ether, 527. 
Nitrous oxide, N 2 0, 140. 

composition by volume, 146. 
identified, 141. 
Nitroxylole, 464. 
N 2 0, nitrous oxide, 140. 
NO, nitric oxide, 141. 
N 2 3 , nitrous anhydride, 143. 
N0 2 , nitric peroxide, 145. 
N 2 5 , nitric anhydride, 134. 
Noble metals, 13. 
Non-metallic elements, 3. 



Nordhausen oil of vitriol, 202. 
Normal alcohols, 521. 

salt, definition, 250. 
Normandy's still, 52. 
Nucleine, 616. 
Nuggets, 400. 
Nutrition of animals, 633. 
plants, 627. 
plastic elements of, 637. 
Nux-vomica, 600. 

O, oxygen, 23. 
Oak bark, 593. 
Occlusion of hydrogen, 40. 
Ochres, 291. 
CEnanthene, 521. 
GEnanthic acid, 519, 583. 

synthesis, 570. 
alcohol, 518. 
GEnanthole, 583. 
Oil of spiraea, 482. 
Oil of vitriol, H 2 S0 4 , 203. 
brown, 207. 
dehydrated, by phosphoric 

acid, 210. 
dissociation of, 210. 
distillation of, 207. 
manufacture, 203. 
sulphate of lead in, 208. 
Oil of wine, 528. 
Oils, 581. 
Olefiant gas, C 2 H 4 , 95. 

absorbed by sulphuric acid, 

210. 
combination with chlorine, 96. 
converted into alcohol, 530. 
decomposed by chlorine, 97. 
heat, 97. 
the spark, 97. 
identification of, 95. 
preparation, 95. 
with iodine, 180. 
Olefines, C„H 2 ",521. 
Oleic acid, HC 18 H 33 2 , 582. 

action of nitric acid on, 583. 
series of acids, 578. 
Oleine, C 57 H 104 O 6 , 582. 

synthesis of, 576. 
Olibanum, 487. 
Oligist iron ore, 300. 
Olive-oil, 581. 
Olivine, 283. 
Onions, 506. 

essential oil of, 485. 
Onyx, 113. 
Oolite limestone, 277. 
Oolitic iron ore, 301. 
Opal, 113. 
Opium, composition, 596. 

extraction of alkaloids from, 596. 
Orange chrome, 2PbO.Cr0 3 , 332. 
Orange, essential oil of, 476. 
Orceine, 606. 
Orcine, 606. 
Ore-furnace, 354. 
Organic analysis, elementary, 84. 

and inorganic substances, 435. 
chemistry, 435. 
compounds classified, 435. 
matter identified, 61. 
substances, definition, 6. 



INDEX. 



667 



Organic substances, synthetical formation, 

92. 
Organo-metallic bodies, 532. 

table of, 538. 
Oriental alabaster, 47. 
Orpiment, red, As 2 S 2 , 244. 

yellow, As 2 S 3 , 245. 
Orthoclase, 295. 
Orthophosphates, 231. 
Orthophosphoric acid, H 3 P0 4 , 231. 
Osmazome, 621. 
Osmic acid, 398. 
Osmiridium, 398. 
Osmium, Os, 398. 

chlorides. 398. 
oxides, 398. 
tetrasulphide, 398. 
Osseiue, 621. 
Oswego, 492. 
Oxalates, 585. 
Oxalethylic acid, 527. 
Oxalic acid, H 2 C 2 4 , 585. 
analysis of, 85. 
fatal dose, 587. 
occurrence in nature, 585. 
preparation, 586. 
properties, 587. 
test for, 587. 
uses, 586. 
ether, 526. 
Oxalonitrile, 551. 
Oxalovinic acid, 527. 
Oxamic acid, 551. 
Oxamide, N 2 H 4 .C 2 2 , 550. 
Oxanilide, 551. 
Oxatyle, 437. 
Oxidation, definition, 24. 

of tissue, products, 636. 
Oxide of copper reduced by hydrogen, 38. 
Oxides, 30. 

metallic, action of hydrochloric acid 
on, 160. 
hydrosulphuric 
acid on, 196. 
sulphuric acid 
on, 210. ■ 
nomenclature of, 30. 
Oxidising blowpipe flame, 109. 
Oxy calcium light, 39. 
Oxygen, O, 23. 

absorption by pyrogallic acid, 595. 

atomicity of, 246. 

blowpipe flame, 110. 

burnt in ammonia, 129. 

combustion in, 25. 

detected in mixed gases, 141. 

determination of, in gases, 36. 

effect on flame, 110. 

electro-negative, 53. 

electro-positive, 53. 

etymology, 27. 

evolved from steam, 152. 

experiments with, 25. 

extracted from air, 30. 

group of elements, 246. 

identified, 9. 

natural sources, 23. 

preparation, 30. 

from air, 30. 
from bichromate of 
potash, 211. 



Oxygen, preparation from chloride o'f lime^ 
162. 
properties, 23. 
purification, 61. 
relation to metals, 27. 

non-metals, 24. 
Oxygenated water, 53. 
Oxygenised muriatic acid, 157. 
Oxyhydrogen blowpipe, 39. 
Oxymuriatic acid, 157. 
Ozokerite, 474. 
Ozone, 54. 

electrolytic, 54. 
experiments with, 55. 
in the atmosphere, 54. 
nature of, 54. 
test for, 55. 
Ozonisation by ether, 56. 

phosphorus, 55. 
Ozonised air, 54. 

oxygen, 54. 
Ozonising tube, 54. 

P, phosphorus, 221. 

Paint blackened by hydrosulphuric acid, 
197. 
luminous, 279. 
removed from clothes, 458. 
Paintings, effect of light and air on, 197. 
Palladamine, hvdrochlorate, 397. 
Palladium, Pd/397. 

carbide, 397. 
chlorides, 397. 
cyanide, 397. 
nitrate, 397. 

occlusion of hydrogen by, 40. 
oxides, 397. 
Palmitic acid; 520. 
Palmitine, C 51 H 98 6 , 573. 

synthesis of, 576. 
Palm-oil, 573, 581. 

bleaching of, 581. 
Pancreatic juice, 635. 
Panification, 499. 
Papaverine, 540. 
Paper, 470. 

action of nitric. acid on, 507. 
dissolved by ammonio-cupric solu- 
tion, 362. 
Paper for cheques, &c, 493. 

for photographic printing, 213. 
Paracyanogen, 443. 
Paraffin, C 16 H 34 , 472. 

extraction, 472. 
oil, 474. 
series, 526. 
Paraguay tea, 598. 
Paraldehyde, 557. 
Paramylene, 521. 
Paranaphthalene, 469. 
Paraniline, 547. 
Parasorbic acid, 591. 
Paratartaric acid, 590. 
Parchment, 594. 

size, 622. 
vegetable, 502. 
Paris yellow, 377. 
Parsley, essential oil of, 476. 
Partial saturation, method of, 571. 
Parting of gold by sulphuric acid, 209. 
Passive state of metals, 321. 



668 



INDEX. 



Patent yellow, 377. 

Pattinson's process, 369. 

Paviine, 485. 

Paving stones, 411. 

Pb. lead, 365. 

PbCl 2 , chloride of lead, 376. 

Pbl 2 , iodide of lead, 377. 

PbO, protoxide of lead, 372. 

PbO.Cr0 3 , chromate of lead, 332. 

PbO.S0 3 , sulphate of lead, 376. 

PbS, sulphide of lead, 377. 

Pd, palladium, 397. 

Pea iron ore, 300. 

Pear flavour, 556. 

Pearlash, 257. 

Pearl hardener, 279. 

Pearls, 73. 

Pearl-spar, 283. 

Pearl white, BiCl 3 , Bi 2 3 , 337. 

Peas, 614. 

Peat-bog, 70. 

composition, 433. 
Pectic acid, 632. 
Pectine, 632. 
Pectose, 632. 
Pectosic acid, 632. 
Pelargonic acid, 519. 
Pentanes, isomeric, 439. 
Pentathionic acid, 215. . 
Pentethylene - tetrethyl - tetrammonium, hy- 
drate, 548. 
Pepper, essential oil of, 476. 
Peppermint, essential oil of, 477. 

Pepsine, 634. 

Peptones, 635. 

Perchlorates, 166. 

Perchloric acid, 166. 

hydrated, 166. 
ether, 527. 

Perchlorokinone, 598. 

Perchromic acid, 333. 

Percussion cap composition, 449. 
fuze, 165. 

Perfume ethers, 556. 

Perfumes, extraction of, 476. 

Periclase, 283. 

Pericline, 295. 

Periodates, 178. 

Periodic acid, 178. 

classification, 256. 

Permanent ink, 382. 

white, 275. 

Permanganate of potash, KMn0 4 , 329. 

Permanganic acid, 329. 

Perspiration of the skin, 569. 

Persulphuric acid, 215. 

Peruvian bark, 597. 

saltpetre, NaN0 3 , 414. 

Petalite, 271. 

Petinine, 548. 

Petrifying springs, 47. 

Petroleum, 98, 473. 

Peucyle, 475. 

Pewter, 346. 

Phenanthraquinone, 469. 

Phenanthrene, 469. 

Phenic acid, 464. 

Phenole, C 6 H 6 0, 464. 

Phenoles, 465. 

Phenose, 459. 

Phenylacetonitrile, 560. 



Phenylamine, 459, 544. 
Phenylaniline, 544. 
Phenyle, C 6 H 5 , 462. 

carbamine, 554. 
ether, 465. 
hydrate, 465. 
Phenylene-diamine, 546. 
Phenylene-ditolylene-triamine, 547. 
Phenylene-ditolylene-triethyl-triamine, 548. 
Phenylene - ditolylene - triphenyl - triamine, 

547. 
Phenylic hydride, 466. 
Phenyl-toluylamine, 544. 
Philosopher's wool, 285. 
Phlogistic theory, 157. 
Phlogiston, 157. 
Phloretine, 484. 
Phloridzeine, 485. 
Phloridzine, 484. 
Phloroglucol, 595. 
Phocenine, 584. 
Phosgene gas, COCl 2 , 170. 
Phosphamides, 236. 
Phosphates, 231. 
Phosphethylic acid, 528. 
Phosphides, 226. 
Phosphine, 233. 
Phosphites, 232. 
Phosphodiamide, 236. 
Phosphoglyceric acid, 576. 
Phosphomolybdate of ammonia, 334. 
Phosphomonamide, 236. 
Phosphor-bronze, 358. 
Phosphorescence, 224. 

prevented, 224. 
Phosphoric acid, 231. 

anhydrous,preparation,230. 
common, 231. 
dibasic, 231. 
di-hydrated, 231. 
glacial, 231. 
molybdic test for, 334. 
monobasic, 231. 
monohydrated, 231. 
tribasic, 231. 
trihydrated, 231. 
anhydride, 230. 
ether, 528. 
Phosphorised oil, 224. 
Phosphorite, 222. 
Phosphorous acid, 232. 
Phosphorus, P, 221. 

action of potash on, 234. 

allotropic modifications, 225. 

amorphous, 225. 

and oxygen, 24. 

bromides, 235. 

burnt under water, 167, 233. 

chemical relations, 226. 

chlorides, 235. 

cyanide, 447. 

distilled, 225. 

fuze composition, 228. 

iodides, 235. 

match- bottle, 224. 

occurrence in nature, 221. 

oxides, 228. 

oxychloride, 235. 

pentachloride, 235. 

action of am- 
monia on, 236,, 



INDEX. 



669 



Phosphorus, poisonous properties, 226. 

precipitation of metals by, 227. 
preparation, 222. 
properties, 223. 
red, 224. 
suboxide, 233. 
sulphides, 236. 
sulphochloride, 235. 
transformed by iodine, 235. 
trichloride, 235. 
vitreous, 223. 
Phosphotriamide, 236. 
Phosphovinic acid, 528. 
Phosphurets, 226. 

Phosphuretted hydrogen, gaseous, PH 3 , 233. 
analogy with am- 
monia, 234. 
composition, 233. 
liquid, 234. 
solid, 234. 
Photographic baths, recovery of silver from, 

383. 
Photographic printing, 213. 
Phthalic acid, 468. 

anhvdride, 469. 
Phyllocyanine, 602. 
Phylloxanthine, 602. 
Physetoleic acid, 578. 
Picamar, 473. 
Picoline, 454. 
Picric acid, 465. 
Picrocyamates, 466. 
Picrotoxine, 485. 
Pig iron, 306. 
Pilocarpine, 540. 
Pimelic acid, 582. 
Pimple metal (copper), 357. 
Pine apple flavour, 556. 
Pinic acid, 476. 
Pink salt, 2NH 4 Cl.SnCl 4 , 349. 
Pins tinned, 345. 
Pipe-clay, 291. 
Piperine, 540. 
Pipette, curved, 83. 
Pit charcoal, 418. 
Pitch, 456, 473. 

mineral, 473. 
Pitchblende. 298. 
Pittacal, 473. 

Plants and animals, reciprocity of, 633. 
changes after death, 632. 
chemical changes in, 630. 
constructive power of, 633. 
food of, 627. 
nutrition of, 627. 
reducing functions of, 632. 
ultimate elements of, 627. 
Plaster of Paris, 278. 

overburnt, 279. 
preparation, 278. 
Platammon - ammonium, hydrated oxide, 

550. 
Platammonium, hydrated oxide, 550. 
Platina, muriate, 395. 
Platinamine, 396. 
Platinates, 394. 
Platinic chloride, PtCl 4 , 395. 
Platinised asbestos, 143. 
Platinochloride of potassium, 2KCl.PtCl 4 , 

395. 
Platinoid metals, general review of, 399. 



Platinous chloride, PtCl 2 , 395. 
Platinum, Pt, 392. 

amalgam, 387. 
ammonio-chloride, 2NH 4 Cl.PtCL, 

395. 
and rhodium alloy, 397. 
attacked by sulphuric acid, 209. 
bichloride, Pt01 4 , 395. 
black, 394. 
corroded, 394. 

by arsenites, 240. 
by phosphorus, 226. 
by silicon, 117. 
crucible heated, 115. 
extraction, 392. 
fulminating, 395. 
ores, analysis, 399. 
oxides, 394. 

protochloride, PtCl 2 , 395. 
separation from iridium, 399. 
spongy, 393. 

stills for sulphuric acid, 207. 
sulphides, 397. 
tetrachloride, PtCl 4 , 395. 
uses of, 393. 
Platosamine, hydrate, 396. 

hydrochlorate, 396. 
sulphate, 396. 
Plato-triethyle-arsonium, chloride, 550. 
-phosphonium, 550. 
-stibonium, 550. 
Plumbago, 63. 
Plumbic acid, 375. 
Pneumatic trough, 90. 
P 2 3 , phosphorous anhydride, 232. 
P 2 5 , phosphoric anhydride, 230. 
Poison-nut, 600. 
Pole, negative, 8. 
positive, 8. 
Pollux, 273. 
Poly ammonias, 545. 
Polyatomic alcohols, 561. 
Polyhalite, 282. 

Polymerising by sulphuric acid, 456. 
Polymerism, 439. 
Poplar, oil of, 476. 
Populine, 484. 
Porcelain, 410. 

English, 410. 
glazed, 410. 
painting, 410. 
Porous cell experiment, 19. 
Porphyry, 295. 
Porter, composition, 498. 
Portland cement, 413. 

stone, 412. 
Port wine crust, 515. 

effect of keeping, 515. 
Positive pole, 8. 
Potash-albite, 295. 
Potash, KHO, 259. 

bicarbonate, KHC0 3 , 260. 
bichromate, K 0.2Cr0 3 , 331. 
bisulphate, KHS0 4 , 135, 211. 
bitartrate, 257, 588. 
bi-urate, 625. 
bulbs, 84. 
caustic, 258. 
chlorate, KC10 3 , 163. 
chromate, K 2 O.Cr0 3 , 331. 
from wool, 257. 



670 



INDEX. 



Potash, fused, 258. 

hydriodate, 180. 
in flesh, 620. 
nitrate, 413. 
permanganate, 329. 
prussiate, K 4 Cy 6 Fe, 440. 
quadroxalate, 587. 
red prussiate, 446. 
sulphate, K 9 S0 4 , 211. 
tartrate, K 2 C 4 H 4 6 , 588. 
Potassamide, NH 2 K, 553. 
Potassium, K, 257. 

action on water, 11. 

alcohol, 530. 

amidide, 553. 

antimoniate, KSb0 3 , 339. 

arsenite, 240. 

atomic weight, 274. 

aurate, 408. 

biantimoniate, 340. 

bicarbonate, 260. 

bimetantimoniate, 340. 

blowpipe test for, 259. 

bromate, 173. 

bromide, 173. 

carbonate, K 2 C0 3 , 257. 

chlorate, KC10 3 , 163. 

chloride, KC1, 260. 

solubility, 418. 

chromate, K 2 Cr0 4 , 331. 

cyanate, KCNO, 449. 

cyanide, KCN, 444. 

dichromate, K 2 Cr 2 7 , 331. 

ethyle, 536. 

extraction, 258. 

ferricyanide, K 3 C 6 N 6 Fe, 446. 

ferrocyanide, K 4 C 6 N 6 Fe, 440. 

fulminurate, 456. 

hydrate, KRO, 258. 

iodate, 176. 

iodide, KI, 180. 

isocyanurate, 456. 

manganate, 328. 

mercaptan, 531. 

metantimoniate, 340. 

metastannate, 348. 

nitrate, KN0 3 , 413. 

oleate, 573. 

osmite, 398. 

oxalates, 587. 

perchlorate, 166. 

permanganate, 329. 

peroxide, 416. 

platinochloride, 395. 

properties, 259. 

silicofluoride, 185. 

sulpharsenite, 245. 

sulphate, K 2 S0 4 , 211. 

sulphide, K 2 S, 426. 

sulphocyanide, KCNS, 450. 

tartrate, 588. 

test for, 42. 

trichromate, 332. 

tri-iodide, 181. 

trithionate, 214. 

urate, 625. 
Potato, composition, 490. 
spirit, 516. 

starch, extraction, 490. 
Pottery, 409. 
Press cake, 420. 



Pressure of gases, 18. 
Preston salts, 268. 
Promethean light, 167. 
Proof spirit, 522. 
Propione, 559. 

Propionic (propylic) acid, 519. 
Propionitrile, 551. 
Propylamine, 548. 
Propylene, 521. 
Propylene-glycol, 564. 
Propylic acid, HC 3 H 5 2 , 519. 

artificial formation, 536. 
alcohol, 518. 
Proteiue, 618. 

Proximate organic analysis, 455. 
Prussian blue, Fe 4 Fcy 3 , 441. 

constitution, 441. 
decomposition by alkalies, 

441. 
native, 323. 
preparation, 441. 
soluble, 441. 
Prussiate of potash, action of sulphuric 

acid on, 90. 
Prussic acid, HCy, 442. 

in bitter almond oil, 481. 
of the Pharmacopoeia, 442. 
Pseudo-carbons, 64. 
Psilomelane, 327. 
Pt, platinum, 392. 
PtCl 2 , platinous chloride, 395. 
PtCl 4 , platinic chloride, 395. 
Ptomaines, 639. 
Pty aline, 634. 

Puddled bar, composition, 312. 
bars, 311. 
steel, 319. 
Puddling, disadvantages of, 313. 
dry, 313. 
loss in, 312. 
mechanical, 313. 
process of, 310. 
Pulvis fulminans, 417. 
Pumice stone, 291. 
Purbeck stone, 412. 
Purple of Cassius, 405. 
Purp urine, 604. 
Putrefaction, 72. 

ammonias furnished by, 548. 
modern researches on, 639. 
Putty powder, 348. 
Pyrene, 469. 
Pyridine, 454. 
Pyrites, arsenical, 236. 

capillary, NiS, 327. 
efflorescent, 202. 

extraction of sulphur from, 189. 
Fahlun, 219. 
oxidation in air, 202. 
white, 202. 
Pyrogallic acid, 595. 
Pyrogalline or pyrogallol, 595. 
Pyroligneous acid, C 2 H 4 2 , 470. 

ether, 471. 
Pyrolusite, Mn0 2 , 327. 

preparation of oxygen from, 
32. 
Pyromucic acid, 569. 
Pyrophoric iron, 91. 
Pyropliorus, lead, 373. 
Pyrophosphates, 231. 



INDEX. 



671 



Pyrophosphoric acid, 2H 2 O.P 2 5 , 231. 
Pyroterebic acid, 578. 
Pyroxylic spirit, 471. 
Pyroxyline, 507. 

QUANTIVALENCE, 247. 

Quantity and tension, electric, 9. 
Quartation of gold, 402. 
Quartz, 113. 

artificial, 115, 528. 
Qnercetine, 485. 
Quercitannic acid, 592. 
Quercitrine, 485. 
Quercitron, 610. 
Quicklime, CaO, 43. 
Quicksilver, 384. 
Quinamine, 598. 
Quince-seed, 490. 
Quinic acid, 598. 
Quinidine, 597. 

extraction, 597. 
Quinine, C^H^N^O^ 597. 

amorphous, 597. 

extraction, 597. 

sulphate, 598. 
Quinoidine, 597. 
Quinoline, 467. 
Quinone, 598. 
Quinotannic acid, 597. 

Eacemic acid, 590. 
Radicals, alcohol, 524. 
Eadishes, essential oil of, 485. 
Railway bars, 312. 
Rain water, 343. 
Raisins, 503. 
Rancid oils, 582. 
Rangoon tar, 473. 
Rational formulae, 85, 435. 
Realgar, As 2 S 2 , 244. 
Reaumur's porcelain, 408. 
Reciprocal combustion, 38. 
Red copper ore, Cu 9 0, 361. 
Red dyes, 609. 

fire, composition for, 165. 

flowers, colouring matter of, 603. 

lead, Pb 3 4 , 374. 

-ore, PbO.Cr0 3 , 332. 

liquor, 265. 
' ochre, 300. 

orpiment, 244. 

paints, 391. 

precipitate, 387. 

-shortness, 314. 

silver-ore, 3Ag 2 S.As 2 S 3 , 237. 

sulphide of antimony, 341. 
Reduced, 30. 

Reducing blowpipe flame, 109. 
Reduction of metals by carbonic oxide, 91. 

on charcoal, 110. 
Refinery, 309. 
Refining cast-iron, 309. 
Refraction of saltpetre, 413. 
Refrigerator, Carre's, 127. 
Regulus, 354. 
Regulus of antimony, 338. 
Rennet, 613. 
Resins, 478. 

Resists (calico-printing), 610. 
Resorcine, 469. 
Respiration, 72. 



Respiration, formation of carbonic acid in, 
72. 
in confined air, 76. 
Retort, 51. 
Rhabdophane, 297. 
Rhodium, Ro, 397. 

oxides, 398. 
sesquichloride, 398.- 
sodiochloride, 398. 
sulphides, 398. 
Rice, composition, 490. 
Ricinoleic acid, 583. 
Rinman's green, 325. 
Rising of bread, 500. 
Rivers, self-purifying power of, 44. 
River-water, 44. 
Ro, rhodium, 397. 
Roasting, effects on sulphides, 198. 

meat, 621. 
Rochelle salt, KNaC 4 H 4 6 , 589. 
Rock crystal, 113. 
oil, 473. 
salt, 260. 
disintegration, 80. 
Roman cement, 413. 
Rosaniline, 460. 

acetate, 461. 

action of potassium cyanide on, 

462. 
triethylic, 462. 
triphenylic, 462. 
Rosette copper, 357. 
Rosiclers, 384. 
Rosin, 476. 

soap, 476. 
Rosolic acid, 454. 
Rotation of crops, 630. 
Rubian, 603. . 
Rubidia, 273. 
Rubidium, Rb, 273. 

platinochloride, 395. 
properties, 273. 

separation from potassium, 395. 
Ruby, 293, 332. 

glass, 404. 
Rue, essential oil of, 558. 
Rufigallic acid, 595. 
Ruhmkorff's induction-coil, 10. 
Rum, 516. 
Rust, 2Fe 2 3 .3H 2 0, 321. 

ammonia in, 132. 
Rusty deposit in waters, 51. 
Ruthenic acid, 399. 
Ruthenium, Ru, 398. 
Rutic acid, 519. 

alcohol, 518. 
Rutile, TiO,, 350. 
Rye flour, 501. 

S, sulphue, 187. 
Saccharide, 506. 
Saccharine matters, 501. 
Safety-lamp, behaviour in mines, 101. 

Davy's, 101. 

precautions in using, 102. 

Stephenson's, 100. 
Safflower, 603. 
Saffron, 603. 
Sago, 492. 
Salad oil, 581. 
Sal-alembroth, 388. 



672 



INDEX. 



Sal-ammoniac, NH 4 C1, 124. 

action on metallic oxides, 

270. 
composition by volume, 270. 
vapour-density of, 270. 
Saleratus, NaHCOa, 265. 
Sal gem, 260. 
Salicine, 482. 

derivatives, 482. 
Salicyle, C 7 H g 9 , 483. 
hydride, 483. 
Salicylic acid, HC 7 H 5 3 , 483. 
Salicylate, potassium, 465. 
Saligeuine, 482. 
Saline waters, 50. 
Saliretine, 483. 
Saliva, 634. 
Sal-polychrest, 211. 
Sal-prunelle, 416. 
Salt-cake, 267. 
Salt as manure, 629. 
common, 260. 
definition, 28. 
etymology, 249. 
extraction, 260. 
fused, 157. 

-gardens of Marseilles, 261. 
-glazing, 410. 
of lemons, 587. 
of sorrel, 587. 
of tartar, 257. 
preservative effect, 639. 
table-, 262. 

useful applications, 262. 
Salting of meat, 621. 
Saltpetre, KN0 3 , 413. 

as manure, 629. 

cubical, NaN0 3 , 414. 

-flour, 415. 

impurities, 416. 

prepared from sodium nitrate, 

414. 
properties, 416. 
refining, 415. 
tests of purity, 416. 
Salt-radicals, 186. 
Salts, acid, 251. 
basic, 251. 
constitution of, 249. 
definition, 249. 
double, constitution, 251. 
haloid, 186, 250. 
mutual decomposition of, 414. 
neutral, 250. 
normal, 250. 
oxyacid, 250. 

water- tvpe theory of, 251. 
Sal-volatile, 269. 
Samarskite, 297. 
Sand, 113. 
Sandarach, 478. 
Sandstone, 411. 

Craigleith, 411. 
Sanitas, 476. 
Sap of plants, 631. 
Saponification by steam, 575. . 

sulphuric acid, 574. 
theory of, 572. 
Saponine, 485. 
Sapphire, 293. 
Sarcosine, C 3 H 7 N0 2 , 620. 



Satin spar, 277. 

Saturated solution, 40. 

Savin, essential oil of, 476. 

Saxon sulphuric acid, 202. 

Saxony blue, 607. 

Sb, antimony, 337. 

SbCl 3 , antimony trichloride, 341. 

SbCl.5, pentachloricle of antimony, 341. 

Sb 2 3 , antimonious oxide, 339. 

Sb 2 5 , antimonic oxide, 339. 

Sb 2 S 3 , antimony trisulphide, 341. 

Scammony, 487. 

Scarlet dyes, 609. 

Scheele's green, CuHAs0 3 , 241. 

prussic acid, 442. 
Scheelite, 351. 
Schlippe's salt, 342. 
Scotch pebbles, 113. 
Scott's cement, 413. 
Scrubber, 453. 
Scurvy-grass, oil of, 486. 
Se, selenium, 219. 
Seal-oil, 584. 
Sea- water, 51. 

extraction of salt from, 261. 
Sea-weed, 175. 
Sebacic acid, 582. 
Secretion, 636. 
Sedative salt, 120. 
Seeds, composition, 630. 

germination, 494. 
Sefstrom's furnace, 321. 
Sel d'or, 405. 
Selenic acid, Se0 3 , 220. 
Selenides, 219. 
Selenietted hydrogen, 220. 
Selenious acid, Se0 2 , 220. 
Selenite, 278. 
Selenium, Se, 219. 

chlorides, 220. 
sulphides, 220. 
Sellaite, 184. 
Seltzer water, 50. 
Separating funnel, 96. 
Sericine, 622. 
Serpentine, 283. 
Serum, 616. 
Shaft, downcast, 78. 

upcast, 78. 
Shamoying, 593. 
Shear-steel, 317. 

Sheep-dipping compositions, 240. 
Shell-lac, 478. 
Sherry, 516. 
Shot, 372. 
Si, silicon, 113. 
Sicilian sulphur, 187. 
Siemens' induction-tube, 54. 

regenerative furnace, 434. 
Sienna, 291. 

SiF 4 , silicon fluoride, 184. 
Signal-light composition, 245. 
Silica, Si0 2 , 113. 

amorphous, 115. 

crystalline, 115. 

dissolved by hydrofluoric acid, 183. 

gelatinous, preparation, 185. 

in plants, 113. 

in waters, 113. 
Silicate of alumina and soda, 295. 
soda, 114. 



INDEX. 



673 



Silicated soap, 573. 
Silicates, 116. 
Silicic acid, 117. 

solution of, 115. 
ether, 528. 
Silicide of magnesium, 119. 
Silicium, 117. 

ethyle, 538. 
methyle, 538. 
Silicofiuoric acid, 185. 
Silicon, Si, 113. 

action of hydrochloric acid on, 171. 
amorphous, 117. 
and nitrogen, 118. 
chloride, SiCl 4 , 170. 
disulphide, 218. 
fluoride, SiF 4 , 184. 
fluoride, preparation, 184. 
fused, 118. 
graphitoid. 117. 
hydride, ll8. 
Silicone, 119. 
Silk. 622. 
Silver, Ag, 378. 

action of hydrochloric acid on, 160. 
hydrosulphuric acid on, 
'196. 
amalgam, 387. 
arsenite, 240. 
basic periodate, 178. 
bromide, AgBr. 384. 
chloride, AgCl,'383. 

action of light on, 213. 
reduction of, 383. 
cleaned, 196. 
coin, 380. 
crucibles, 382. 
detected in lead, 372. 
extracted from its ores, 379. 
extraction by amalgamation, 379. 
from copper-ores, 379. 
lead, 370. 
frosted, 380. 

fulminate, Ag 2 C. 2 NoOo, 450. . 
fnsing-point, 381. 
fulminating-, 384. 
glance, Ag 2 S, 384. 
hyposulphite, 213. 
in lead, 369. 
iodide, 178. 
metaphosphate, 232. 
native, 379. 
nitrate, AgX0 3 , 382 

preparation from standard 
silver, 382. 
nitride, 382. 
ore, red, 384. 
oxalate, 587. 
oxide, Ag.,0, 382. 
oxides, 382. 
oxidised, 380. 
periodate, 178. 
plate, 380. 
properties, 381. 
pure, preparation, 381. 
pyrophosphate, 232. 
recovered from photographic baths, 

383. 
refining, 371. 

separated from copper, 379. 
solder, 380. 



Silver, stains removed, 382. 
standard, 380. 
subchloride, 383. 
sulphide, Ag 2 S, 384. 
native, 384. 
tarnished, 196. 
tree, 387. 
triphosphate, 231. 
Silvering brass or copper, 381. 
dry, 381. 
glass, 381. 
Simple solution, 40. 
Si0 2 , silica, 113. 
Siphon eudiometer, 36. 
Size, 622. 

Slag, blast furnace, composition, 305. 
iron in, 308. 
iron-refinery, 309. 
lead-furnace, 367. 
metal (copper), 355. 
ore-furnace, 354. 
puddling-furnace, 312. 
refinery (copper), 356. 
roaster (copper), 355. 
j Slaked lime, Ca(HO) 2 , 278. 
I Slaking of lime, 43. 
I Slate, 291. 
; Slow portfire, 416. 
i Smalt, 325. 
! Smelling-salts, 268. 
j Smoke, cause of, 70. 

consumption, 70. 
prevention, 70. 
Smokeless gas-burners, 107. 
Sn, tin, 342. 

SnClo, protochloride of tin, 348. 
S11CI4, bichloride of tin, 348. 
SnO, protoxide of tin, 347. 
Sn0 2 , binoxide of tin, 347. 
Snow, 52. 

SnS, protosulphide of tin. 349. 
SnS 9 , bisulphide of tin, 249. 
Snuff, 602. 

50 2 , sulphurous anhvdride, 198. 

50 3 , sulphuric „ 202. 
Soap, 572. 

arsenical, 240. 

Castile, 573. ' 

glycerine, 573. 

mottled, 573. 

-nut, 485. 

palm-oil, 573. 

rosin in, 573. 

silicated, 573. 

transparent, 573. 

-wort, 485. 

yellow, 573. 
Soaps decomposed by acids, 574. 
Soda, NaHO, 265. 

action on hard waters, 48. 

arseniates, 242. 

ash, 263. 

manufacture, 263. 

biborate, 266. 

bicarbonate, 265. 

bimetantimoniate, 340. 

bitungstate, 351. 

carbonate, Xa 2 O.C0 2 , 265. 

manufacture from common 

salt, 262. 
medicinal, 265. 

2 U 



674 



INDEX. 



Soda, caustic, NaHO, 265. 
chloride, 163. 
common phosphate, 2NaoO.HoO.Po0 5 , 

231. 
crystals, 263. 
hydrate, 265. 
hyposulphite, Na 2 S 2 3 , 212. 

use in photography, 
213 
in blood, 618. 
-lime, 131. 
-lye, 265, 572. 
manufacture of, history, 262. 

influence on useful 
arts, 263. 
nitrate, 268, 414. 

conversion into nitrate of 

potash, 414. 
solubility, 414. 
obtained from kyrolite, 265. 
sulphate, Na 3 O.S0 3 , 267. 

extracted from sea-water, 
261. 
washing, 263. 
-waste, 264. 
-water, 80. 

powders, 80. 
Sodacetic ether, 570. 
SodanMe, NH 9 Na, 553. 
Sodium, Na, 26a 

action on water, 13. 
alcohol, 531. 
aluminate, 294. 
amalgam, 131. 
and oxygen, 27. 
arseniates, 242. 
arsenite, 240. 
aurochloride, 405. 
blowpipe test for, 265. 
borate, 266. 
carbonate, 265. 
chloride, 260. 

commercial importance, 147. 
solubility, 414. 
equivalent weight, 13. 
ethylate, 531. 
ethyle, 536. 
extraction, 265. 
fluoride, 184. 
glycol, 562. 
hydrate, NaHO, 265. 
hydrosulphite, 214. 
hypochlorite, 163. 
hvpophosphite, 233. 
hyposulphite, Na 2 S 2 3 , 212. 
line in the spectrum, 273. 
manganate, 328. 
metaphosphate, 231. 
nitrate, 414. 

solubility, 414. 
nitroprusside, 447. 
oleate, 573. 
palmitate, 573. 
pentasulphide, 214. 
periodate, 178. 
phosphate, Na 2 HP0 4 , 231. 
platinate, 394. 
platinochloride, 395. 
pyrophosphate, 232. 
silicate, 267. 
silicotiuoride, 117. 



Sodium, stannate, 578. 
stearate, 573. 
sulphantimoniate, 197. 
sulpharseniate, 197. 
sulphate, Na 2 S0 4 , 267. 
sulphite, 201. 
sulphostannate, 197. 
sulphoxy phosphate, 235. 
tetrathionate, 214. 
tungstate, Na 2 W0 4 , 351. 
urate, 625. 
Soffioni, 120. 

artificial, 120. 
Softening waters, 48. 
Soft soap, 573. 
water, 45. 
Soils, formation, 80, 628. 
impoverished, 628. 
iron in, 322. 
Solanine, 540. 
Solder, 346. 

brazier's, 360. 
coarse, 346. 
fine, 346. 

silversmith's, 380. 
Soldering, use of sal-ammoniac in, 271. 
Soluble glass, 267. 
Solution, 40. 
Soot, 71. 

as manure, 622. 
Sorbic acid, 591. 
Sorbite, 507. 
Sorrel, salt of, 587. 
Soup, 621. 
Spanish black, 64. 
Sparkling wines, 80. 
Sparteine, 540. 
Spathic iron ore, FeC0 3 , 301. 
Specific gravity of gases defined, 16, 23. 

influence of tem- 
perature on, 193. 
liquids, defined, 52. 

determined, 126. 
solids, defined, 52. 
Specific heat defined, 43l. 

relation to atomic weights. 
283. 
Specific heats of potassium, sodium, and 

lithium, 280. 
Spectroscope, 272. 
Spectrum analysis, 272. 

use of carbon disulphide 
in, 216. 
Specular iron ore, Fe 2 3 , 300. 
Speculum metal, 347, 360. 
Speiss. 325. 
Spelter, 286. 
Spermaceti, 584. 
Sperm oil, 584. 
Spheroidal state, 199. 
Spices, preservative effect of, 639. 
Spiegel-eisen, 319. 
Spindle, MgO.Al 2 3 , 293, 322. 
Spirit, methylated, 479. 
of sait, 148. 
of wine, 522. 
Spirits, 516. 

of turpentine, 474. 
Spiritus rectificatus, 522. 

tenuior, 522. 
Spirting avoided, 116. 



INDEX. 



675 



Sponge, 622. 

ashes of, 175. 
Spongy platinum, 392. 
Spontaneous combustion of oils, 583. 

phosphorus, 24. 
Springs, petrifying, 47. 
Spring water, 43, 80. 
Sprouting of silver, 371. 
Sr, strontium, 276. 
Sr 2 C0 3 , strontium carbonate, 276. 
SrO, strontia, 279. 
Sr(N0 3 ) 2 , strontium nitrate, 276. 
SrS0 4 , strontium sulphate, 276. 
Stains of fruit removed, 200. 
Stalactites, 47. 
Stalagmites, 47. 
Stannates, 348. 
Stannic acid, 348. 

clialvsed, 348. 
chloride, SnCl 4 , 349. 
oxide, Sn0 2 , 347. 
sulphide, SnS 2 , 349. 
Stannous chloride, SnCl 2 , 348. 
oxide, SnO, 347. 
sulphide, SnS, 349. 
Star antimony, 337. 
Starch, C 6 H 10 O 5 , 490. 

action of water on, 492. 
a glucoside, 496. 
and iodine, 177. 
blue, 296. 
commercial, 491. 
extraction from potatoes, 490. 
rice, 491. 
wheat, 491. 
from different plants, distinguished, 

491. 
in food, 492. 
iodised, 493. 
paste, preparation, 55. 
Stassfurthite, 260, 414. 
Steam, composition by volume, 36. 
decomposed by carbon, 89. 

chlorine, 153. 
electric sparks, 10. 
heat, 10. 
latent heat of, 432. 
specific gravity calculated, 53. 
Stearic acid, HC 18 H 35 2 , 520, 574. 

glucose, 579. 
Stearine, C 57 H 110 O 6 , 572. 
candles, 574. 
synthesis of, 575. 
Steatite, 281. 
Steel, 315. 

annealing, 317. 

Bessemer, 318. 

blistered, 316. 

cast, 317. 

distinguished from iron, 318. 

German, 319. 

hardening, 317. 

Krupp's, 319. 

made with coal gas, 318. 

manufacture, 315. 

natural, 319. 

nitrogen in, 318. 

puddled, 319. 

shear, 317. 

tempering, 317. 

tilted, 316. 



Steel, titanium in, 318. 
Stereochromy, 267. 
Sterro-metal, 360. 
Stibethvle, Sb(C 2 H 5 ) 3 , 537. 
Stibiotriethyle, 537. 
Stibio-trimethyle, 537. 
Still, 51. 

Stockholm tar, 473. 
Stone, artificial, 267. 
-coal, 71. 
decayed, 412. 
test of durability, 412. 
-ware, 410. 
Storax, 477. 

Stout, composition, 498. 
Straits tin, 344. 
Stream-tin ore, 342. 
Strontia, 276. 
Strontianite, 276. 
Strontium, Sr, 276. 

carbonate, 276. 
nitrate, Sr(N0 3 ) 2 , 276. 
properties, 276. 
sulphate, 276. 
sulphide, 276. 
Structural formula, 436. 
Struvite, 283. 

Strychnine, C 21 H 22 N 2 2 , 600. 
extraction, 601 . 
identified, 601. 
properties of. 601. 
Stucco, 279. 
Styracine, 477. 
Styrole, 478. 
Styrolene, 95, 478. 
Suberic acid, 582. 
Suberine, 489. 
Sublimate, corrosive, 388. 
Sublimation, 124, 479. 
Sublimed sulphur, 419, 
Substitution, 154. 

of chlorine for hydrogen, 467. 
Substitutive formulae, 87. 
Succinic acid, H 2 C 4 H 4 4 , 478, 582. 

conversion into tartaric, 589. 
formed from tartaric, 589. 
synthesis of, 590. 
Succussion, 207. 
Suet, 584. 

Sugar, action of oil of vitriol on, 208. 
adulteration, 501. 
-candy, 505. 
-cane, composition, 503. 
extraction, 503. 
from beet-root, 505. 
linen, &c, 502. 
-lime, 506. 
loaf, 505. 
maple, 505. 
of flesh, 620. 
of fruits, C 6 H]o0 6 , 503. 
of gelatine, 622". 
of manna, 506. 
of milk, C 12 H 24 12 , 614. 
preservative effect of, 639. 
raw, 504. 
-refining, 504. 
starch, 501. 
uncrystallisable, 503. 
with lead oxide, 506. 
with sodium chloride, 506. 



676 



INDEX. 



Sugars, 501. 

chemical properties, 505. 
optical properties, 506. 
Sulphamylic acid, 529. 
Sulphanthraquinonic acid, 605. 
Sulphantimoniates, 342. 
Sulphantimonites, 342. 
Sulpharseniate, cuprous, 245. 
Sulpharsenic acid, 245. 
Sulpharsenious acid, 245. 
Sulphate of soda and lime, 267. 

crystallisation of, 41. 
composition, 42. 
Sulphates, 210. 

acid, 211. 

action of heat on, 211. 
double, 211. 
in common use, 211. 
native, 187. 
normal, 211. 

reduced to sulphides, 212. 
Sulphethylic acid, C 2 H 5 HS0 4 , 528. 
Sulphides, 197. 

action of air on, 197. 
native, 187. 

precipitated by hyposulphites, 
213. 
Sulphindigotic acid, 608. 
Sulphindylic acid, 608. 
Sulphites, 201. 
Sulphobenzolic acid, 464. 
Sulphocarbimides, 486. 
Sulphocarbonates, 217. 
Sulphocarbonic acid, 217. 
Sulphochromites, 333. 
Sulphocyanide of ammonium, preparation, 

217. 
Sulphocyanogen, CyS, 445. 
Sulphoglyceric acid, 576. 
Sulpholeic acid, 575. 
Sulphopalmitic acid, 575. 
Sulphophosphotrianhde, 236. 
Sulphosaccharic acid, 506. 
Sulphostearic acid, 575. 
Sulphovinic acid, C 2 H 5 HS0 4 , 528. 
Sulphoxyphosphoric acid, 235. 
Sulphur, S, 187. 

-acids, 198. 

action of alkalies on, 193. 

lime on, 198. 
allotropic states of, 190. 
amorphous or insoluble, 190. 
and oxygen, 26. 
bases, 197. 

chemical relations, 193. 
chloride, S 2 C1 2 , 219. 
combining volume, 193. 
dichloride, SC1 2 , 218. 
dimorphous, 192. 
distilled, 188. 
ductile, 191. 
electro-negative, 191. 
electro-positive, 19 i. 
examination of, 419. 
extraction, 187. 

from copper-pyrites, 

189. 
from iron-pyrites, 189. 
from soda-waste, 264. 
flowers of, 188. 
for gunpowder, 419. 



Sulphur, function in gunpowder, 419. 
group of elements, 221. 
home sources of, 189. 
iodide, SI.„ 219. 
milk of, 190. 

occurrence in nature, 187. 
octahedral, 192. 
of coal-mines, 102. 
ores, 187. 
oxides, 198. 

oridised and dissolved, 193. 
by nitric acid, 137. 
plastic, 191. 
prismatic, 192. 
properties, 190. 
refining, 188. 
roll, 188. 
rough, 188. 
-salts, 197. 
subiodide, S 2 I 2 , 219. 
sublimed, 188. 
test for, 448. 
uses, 190. 

vapour density, 193. 
washed, 419. 
Sulphureous waters, 50. 
Sulphuretted hydrogen, HoS, 194. 
Sulphuric acid, H 2 S0 4 , 202". 

action on bromides, 174. 
copper, 199. 
fats, 575. 
fluor-spar, 182. 
lead, 207. 
metallic oxides. 

210. 
metals, 209. 
organic matters, 

209. 
silver, 209. 
anhydrous, 210. 

preparation, 210. 
caution in diluting, 208. 
attraction for water, 208. 
combinations with water. 

209. 
concentrated, 208. 
concentration, 207. 
decomposition by heat, 210. 
diluted, turbidity of, 208. 
distillation of, 207. 
formation, 203. 
from the chambers, 206. 
fuming, 202. 
glacial, 210. 
manufacture, 204. 

chemical prin- 
ciples, 203. 
history of, 203. 
illustrated, 

203. 
summary, 208. 
Nordhausen, 202. 
polymerising by, 456. 
reduced by hvdriodic acid, 

179. 
vapour-density of, 210. 
anhydride, 210. 
ether, 522, 528. 
Sulphuring casks, 201. 
Sulphurous acid, H 2 S0 3 , 199. 

a reducing agent, 201. 



INDEX. 



677 



Sulphurous acid, action on hydrosulphuric 
acid, 215. 
nitric acid, 203. 
nitric peroxide, 

203. 
zinc, 214. 
properties, 200. 
reduced by phosphorous 
acid, 232. 
anhydride, 198. 
Sulphuryle, 201. 
Sumach, 593. 

Superphosphate of lime, 222. 
Supersaturated solution, 41. 
Sioedish iron ore, 301. 
Sweet oil, 581. 
Sweet spirits of nitre, 527. 
Syenite, 296. 
Sylvic acid, 476. 
Symbols, 4. 
Sympathetic ink, 43. 
Synaptase, 480. 
Synthesis of acetic acid, 536, 566. 

acids of the acetic series, 569. 

butyric acid, 570. 

formic acid, 568. 

guanidine, 547. 

hippuric acid, 627. 

hydrocyanic acid, 95. 

leucic acid, 563. 

natural fats, 575. 

organic substances, 92, 435. 

propylic acid, 536. 

prussic acid, 95. 

taurine, 635. 

nrea, 623. 

volatile fatty acids, 569. 

water, 33. 

by weight, 37. 

Tagilite, 363. 
Talc, 281. 
Tallow, 572, 584. 
Tank-waste, 212. 
Tannic acid, 592. 
Tannin, 592. 
Tanning, 592. 
Tannomelanic acid, 594. 
Tantalic acid, 352. 
Tantalite, 352. 
Tantalum, Ta, 352. 
Tap-cinder, composition, 312. 
Tapioca, 492. 
Tar-charcoal, 419. 
Tar, coal, 453. 

wood, 471. 
Tarragon, essential oil of, 482. 
Tartar, 588. 

salt of, 257. 
-emetic, 589. 
Tartaric acid, H 2 C 4 H 4 06, 588. 

artificial formation, 589. 
conversion into malic acid, 

589. 
conversion into succinic acid, 

589. 
formed from succinic acid, 
589. 
anhydride, 588. 
Tartrate of potash and soda, 589. 
Taurine, C 2 H 7 N0 3 S, 635. 



Taurine, artificial formation, 635. ' 

Taurocholic acid, 635. 

Tawing, 593. 

Te, tellurium, 220. 

Tea, composition, 599. 

Telluretted hydrogen, 221. 

Telluric acid, 221. 

Telluride of bismuth, 220. - 

Telluride of potassium, 220. 

Tellurium, Te, 220. 

characterised, 221. 
foliated, 220. 
graphic, 220. 
sulphides, 221. 
Tellurous acid, 221. 
Temper spoilt, 318. 
Tempering, coloiirs in, 318. 
Tenacity of copper, 301. 

iron, 301. 
Tendons, 621. 
Tennantite, 237. 
Terbia, 300. 
\ Terebene, 475. 
Terebilene, 475. 
Terne-plate, 345. 
Terpenes, 476. 
Terpinole, 475. 
Terstearine, 576. 
Test tube, 32. 
Tetrad elements, 248. 
Tetramethylium, hydrate, 543. 
Tetramines, 548. 
Tetramylium, hydrate, 543. 
Tetrathionic acid, 214. 
Tetratomic elements, 248. 
Tetrethylarsonium, hydrate, 549. 
Tetrethylium, hydrate, N(C 2 H 5 ) 4 EO, 543. 

- iodide, 542. 
Tetrethylphosphonium, hydrate, 549. 
Tetrethylstibonium, hydrate, 549. 
Tetrethyl-urea, 625. 
Thallium, Tl, 377. 

alcohol, 531. 

extracted from flue-dust, 377. 
for green fire, 378. 
salts, 378. 
Theine, C 8 H, N 4 O 2 , 598. 
Thenardite, 267. 
Theobromine, C 7 H 8 N 4 2 , 600. 

converted into caffeine, 600. 
Thiocarbonates, 217. 
Thionyle, 201. 
Thiosinnamine, 540. 
Thorina, 297. 
Thorinum, Th, 297. 
Thorite, 297. 

Thyme, essential oil of, 476. 
Tile copper, 357. 
Tiles, 411. 
Tin, Sn, 342. 

action of acids on, 347. 

nitric acid on, 347. 
on hydrosulphuric acid, 196. 
Avater, 13. 
alloys of, 346. 
amalgam, 387. 
bichloride, SnCl 4 , 349. 
binoxide, Sn0 2 , 347. 
bisulphide, SnS 2 , 349. 
boiling, 344. 
crystals, 348. 



678 



INDEX. 



Tin, dichloride, 349. 
disulphide, 349. 
dropped, 344. 

extraction in the laboratory, 344. 
foil, 345. 
grain, 344. 
identified, 344. 
impurities, 347. 
metallurgy of, 342. 
nitromuriate, SnCl 4 , 349. 
Tin-ore of Montebras, 352. 
Tin-ores, mechanical treatment of, 343. 
oxy chloride, 349. 
plate, 345. 
properties of, 344. 
protochloride, SnCl 2 , 348. 
protosulphide, SnS, 349. 
protoxide, SnO, 347. 
pure, preparation, 347. 
pyrites, SnS, 349. 
refining bv liquation, 344. 
salts, 348." 
sesquioxide, 348. 
stannate, 348. 
-stone, Sn0 2 , 342. 
tetrachloride, 349. 
Tin tree, 349. 
Tincal, 119. 

refining of, 266. 
Tinned iron, 345. 
Tinning brass, 345. 

copper, 345. 
Tin-white cobalt, CoAs 2 , 324. 
Titanic acid, 350. 

dialysed, 350. 

extracted from iron-sand, 350. 
hydrated, 350. 
properties, 350. 
Titanic iron, 301. 
Titanium, Ti, 350. 

bichloride, 350. 
bisulphide, 351. 
cyanonitride, 350. 
metallic, 350. 
nitride, 350. 
protoxide, 351. 
sesquichloride, 351. 
sesquioxide, 351. 
Tl, thallium, 377. 
Toast, 492. 
Tobacco, 601. 
Tokay, 516. 
Tolu balsam, 477. 

essential oil, 476. 
Toluene- sulphonic acid, 464. 
Toluidine, 461, 544. 
Toluene, C 7 H 8 , 454. 
Tolylene, 547. 

diamine, 547. 
Tonka bean, 484. 
Topaz, 184, 293. 
Touch-paper, 416. 
Touch-stone, 137. 
Toughening steel, 317. 
Translation, rate of, 18. 
Trap-rock, 296. 
Treacle, 503. 
Tree-wax of Japan, 585 
Triacetine, 565. 
Triacid triamines, 547. 
Triad elements, 248. 



Triamines, 547. 
Triamylamine, 543. 
Triatomic elements, 248. 
Tribasic formic ether, 554. 
Tribasic phosphates, 231. 

phosphoric acid, 231. 
Tribenzoyl-phosphide, 552. 
Tribenzylamine, 560. 
Triborethyle, B(C 2 H 5 ) 3 , 537. 
Tribromo-phenole, 465. 
Tricetylamine, 543. 
Trichloracetic acid, HC 2 C1 3 2 , 566. 
Trichloraniline, 550. 
Trichlorhydrine, 576. 

of phenose, 459. 
Triethylamine, N(C 2 H 5 ) 3 , 542. 
Triethylarsine, As(C 2 H 5 ) 3 , 536, 549. 
Triethylene - octethyl - tetrammonium, hy- 
drate, 549. 
Triethylene-tetralcohol, 565. 
Triethylene-tetramine, 548. 
Triethylene-triamine, N 3 H 3 (C.,H 4 ) 3 , 547. 
Triethylphosphine, P(CoH 5 ) 3 , 549. 
Triethylstibine, Sb(C 2 H 5 ) 3 , 549. 
Trimethylamine, 548. 
Trimethylarsine, 536. 

glycocine, 622. 
Trinitro-cellulose, 509. 
Trinitrocresylic acid, 466. 
Trinitrophenic acid, 465. 
Triphane, 271. 
Triple phosphate, 283. 
Tripotassamide, NK 3 , 553. 
Trithionic acid, 214. 
Tungsten, W, 351. 

binoxide, 351. 

blue oxide, 351. 

chlorides, 352. 

metallic, 352. 

separated from tin ores, 344. 

steel, 352. 

sulphides, 352. 

test for, 351. 
Tungstic acid, 351. 

dialysed, 351. 
Tungstoborates, 351. 
Turbith or turpeth mineral, 388. 
Turkey red, 603. 
Turmeric, 605. 

action of boracic acid on, 121. 
Turnbull's blue, Fe 3 Fdcy, 446. 
Turner's yellow, 377. 
Turpentine, C 10 H 16 , 474. 

action of nitric acid on, 138. 
hydrates, 475. 
hydrocarbons, 476. 
in chlorine, 153. 
Turquoise, 296. 
Tuyere pipes, 302. 
Type furniture alloy, 369. 
Type-metal, 336, 372. 
Types, chemical, 247.- 

Ulmate of ammonia as manure, 622. 
Ulmic acid, 633. 
Ultramarine, artificial, 296. 

green, 296. 
Umber, 291. 
Upcast shaft, 78. 
Uranium, U, 298. 

oxides, 298. 



INDEX. 



679 



Urea, CH 4 N 2 0, 623. 
analysis of, 131. 
artificial formation, 623. 
chemical constitution, 624. 
extraction from urine, 623. 
isomeric with ammonium cyanate, 623. 
nitrate, 623. 
Ureides, 625. 
Uric acid, H 2 C 5 H 2 N 4 3 , 625. 

action of nitric acid on, 625. 
dibasic, 625. 
extraction, 625. 
Urine, 622. 

as manure, 629. 
composition. 627. 
putrefaction of, 623. 

Vacuum-pans, 504. 

Valentinite, 339. 

Valerian, essential oil of, 476. 

Valerianic acid, HC 5 H 9 2 , 519, 571. 

Valerian root, 571. 

Valerine, 584. 

Valerolactic acid, 563. 

Vanadic acid, 335. 

Vanadium, V, 335. 

chlorides, 335. 
ink, 335. 
metallic, 335. 
oxide, 335. 
Vauilline, 484. 
Vapour-densities, influence of temperature 

on, 193. 
Vapour densities of the olefines, 521. 
Varnishes, 479. 
Vasculose, 469. 
Vaseline, 474. 
Vegetable parchment, 209. 
Vegetation, chemistry of, 627. 
Venetian red, 322. 
Venice turpentine, 474. 
Ventilation, illustrations of. 78. 

necessity for, 77. 
Veratrine, 540. 
Verdigris, 566. 
Verditer, 363. 
Vermilion, HgS, 391. 
Vert de Guignet, 332. 
Vesta matches, 167. 
Vinegar, composition, 499. 
French, 499. 
malt, 499. 
manufacture, 498. 
mother of, 499. 
sulphuric acid in, 499. 
white wine, 499. 
Vinic acids, 528. 
Viridine, 544. 
Vitelline, 619. 
Vitriol-chambers, 204. 

corrosive properties of, 208. 
Vivianite, 323. 
Volcanic ammonia, 266. 
Volcano, artificial, 193. 
Voltameter, 35. 

Volume of gas, calculation of, 16, 
Vulcanised caoutchouc, 488. 
Vulcanite, 488. 

W, TUNGSTEN, 351. 

Wad, 327. 



Walls, efflorescence on, 267. 
Washing precipitates, 116. 
Wash-leather, 593. 

Watch-spring for burning in oxygen, 29. 
Water, H 2 0, 7. 

action upon metals, Pi. 
analysis, 7. 

chemical relations of, 40. 
crystallisation of, 52. 
decomposed by battery, 7. 

heat, 10. 
distilled, 51. 
electrolysis of, 7. 
from natural sources, 43. 
-gas, 89. 
hard, 45. 

of constitution, 42. 
of crystallisation, Aq., 42. 
oxygenated, 53. 
purification, 51. 
soft, 45. 
synthesis, 33. 
tested for impurity, 49. 
Waterproof cloth, 487. 

felt, 488. 
Waters, ammonia detected in, 390. 

mineral, 50. 
Water-type theory of acids and salts, 251, 
Waterv vapour, 52. 
Wavellite, 296. 
Wax, bees', 585. 

bleaching, 585. 
Chinese, 584. 
Weld, 603. 
Welding, 315. 

Weldon's chlorine process, 148. 
Well-water, 44. 
Welsh coal, -71. 
Whale-oil, 584. 
Wheat, composition, 490. 

sprouted, 494. 
Wheaten flour, 499. 
Whev, 614. 
Whisky, 516. 
White gunpowder, 166. 
iron, 307. 
lead, 375. 

manufacture, 375. 
ore, PbO.C0 2 , 366. 
metal, Cu 2 S, 355. 
precipitate, NH 2 HgCl, 389. 

fusible, 389. 
vitriol, 288. 
Willow-bark, bitter principle, 482. 
Windows,, crystals on, 268. 
Wine, 514. 
Wines, dry, 515. 

fruity, 515. 

proportion of alcohol in, 514. 
red, 515. 
ropy, 498. 
white, 515. 
Winter-green oil, 472. 
Wire iron, 312. 
Witherite, BaO.COo, 274. 
Wolfram, 342, 451." 
Wood, carbonisation, 64. 
-charcoal, 64. 
combustion, 64. 
composition, 469. 
destructive distillation, 65, 469. 



680 



INDEX. 



Wood, for gunpowder-charcoal, 418. 

-naphtha, CH 4 0, 471. 

preservation of, 633. 

-smoke, 639. 

-spirit, 471. 

-tar, 471. 
Woody fibre, 469. 
Wool, 622. 

Wool and cotton, separation, 622. 
Worm, 51. 
Wormwood, 479. 
Wort, 495. 
Wrought iron, 308. 

Xylenes, 459. 

Xylene-sulphonic acid, 464. 
Xylidine, 464. 
Xyloidine, 514. 
Xylole, 454. 

Yeast, 496. 

dried, 496. 
Yellow, chrome, 332. 

dyes, 603. 

fire, composition for, 266. 

flowers, 603. 

ochre, 300. 

orpiment, 245. 

Paris, 377. 
Ytterbium, 297. 
Yttrium, Y, 297. 
Yttrotantalite, 352. 

Zapfre, 325. 
Zinc, Zn, 284. 
Zinc-acetimide, 553. 

action of air on, 284. 

hydrochloric acid on, 159. 
sulphuric acid on, 288. 
on water, 13. 



Zinc-alcohol, 535. 

-amalgam, 387. 

amalgamated, 386. 

amide, 553. 

amyie, 536. 

and oxygen, 28. 

arsenide, 242. 

arsenite, 240. 

boiling-point, 285. 

carbonate, 285. 

chloride, 289. 

dissolved by potash, 288. 

distilled, 285. 

ethyle, Zn(C 2 H 5 ) 2 . 536. 

extraction, 285. 

Belgian method, 286. 
English method, 285. 
Silesian method, 287. 

granulated, 14. 

hydrosulphite, 214. 

hyposulphite, 214. 

identified, 288. 

impurities in, 288. 

metallurgy of, 285. 

-methyle, 535. 

nitride, 553. 

ores, 284. 

oxide, ZnO, 288. 

in glass, 408. 

oximide, 553. 

phenylimide, 553. 

removal of lead from, 287. 

sulphate, ZnS0 4 , 288. 

sulphide, 285. 

valerianate, 571. 
Zinc-white, -288. 
Zircon, 297. 
Zirconia, 297. 
Zirconium, Zr, 297. 
ZnS, zinc sulphide, 283. 



ERRATUM. 

On page 123, line 32, for "1872" read "1772.' 



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3 


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25 


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5 


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GOODHART AND STARR. A MANUAL OF THE DIS- 
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Part I. — Continued, Eruptive and Periodical Fev- 
ers, Diseases of the Stomach, Intestines, Peritoneum, 
Biliary Passages, Liver, Kidneys, etc (including Tests 
for Urine), General Diseases, etc. 

Part II. — Diseases of the Respiratory System (in- 
cluding Physical Diagnosis), Circulatory System and 
Nervous System ; Diseases of the Blood, etc. 

*** These little books can be regarded as a full set of 
notes upon the Practice of Medicine, containing the 
Synonyms, Definitions, Causes, Symptoms, Prognosis, 
Diagnosis, Treatment, etc., of each disease, and includ- 
ing a number of prescriptions hitherto unpublished. 

No. 4. Physiology, including Embry- 
ology. Second Edition. By Albert P. 
Brubaker,m.d., Prof, of Physiology, Penn'a 
College of Dental Surgery; Demonstrator 
of Physiology in Jefferson Med. College, 
Phila. Revised and Enlarged. 
" This is a well written little book." — London Lancet. 

No. 5. Obstetrics. Illustrated. Second 
Edition. For Physicians and Students. 
By Henry G. Landis, m.d., Prof, of Ob- 
stetrics and Diseases of Women, in Starling 
Medical College, Columbus. Revised Ed. 
New Illustrations. 

" We have no doubt that many students will find in 
it a most valuable aid." — The Amer.JL of Obstetrics. 

No. 6. Materia Medica and Therapeu- 
tics. Second Revised Edition. "With 
especial Reference to the Physiological Ac- 
tions of Drugs. For the use of Medical, 
Dental and Pharmaceutical Students, and 
Practitioners. Based on the New Revision 
(Sixth) of the U. S. Pharmacopoeia, and 
including many unofficinal remedies. By 



Samuel O. L. Potter, m.a., m.d., late A. 
A. Surg. U. S. Army. Revised Edition, 
with Index. 

" One of the very best we have ever seen." — Southern 
Clinic. 

No. 7. Inorganic Chemistry. New Edi- 
tion. By G. Mason Ward, m.d., Demon- 
strator of Chemistry in Jefferson Med. Col- 
lege, Phila. Including Table of Elements 
and various Analytical Tables. New Ed. 

" This neat pocket volume is a brief but excellent 
compend of inorganic chemistry and simple analysis of 
the metals." — Pharmaceutical Record, N. Y. 

No. 8. Visceral Anatomy. Illustrated. 
By Samuel O. L. Potter, m.a., m.d., late 
A. A. Surg. U. S. Army. With 40 Illus. 

" Worthy our recommendation to students, and a 
ready reference to the busy practitioner." — Chicago 
Med. Times. 

No. 9. Surgery. Second Edition. Illus- 
trated. Including Fractures, Wounds, 
Dislocations, Sprains, Amputations and other 
operations; Inflammation, Suppuration, Ul- 
cers, Syphilis, Tumors, Shock, etc. Dis- 
eases of the Spine, Ear, Eye, Bladder, Tes- 
ticles, Anus, and other Surgical Diseases. 
By Orville Horwitz, a.m., m.d., Resident 
Physician Pennsylvania Hospital, Phil'a. 
Second Edition, Revised and Enlarged. 
With 62 Illustrations. 

" Will prove very useful, both to the student and 
practitioner." — Valentine Mott, m.d., Ass 't to the 
Prof, of Surgery , Bellevue Hospital, New York. 

No. 10. Organic Chemistry. Including 
Medical Chemistry, Urine Analysis, and the 
Analysis of Water and Food, etc. By Henry 
Leffmann, m.d., Demonstrator of Chemis- 
try in Jefferson Med. College; Prof, of 
Chemistry in Penn'a College of Dental 
Surgery, Philadelphia. 

" It is a useful and valuable addition to the series of 
Quiz-Compends." — College and Clinical Record. 

No. n. Pharmacy. By Louis Genois, 
PH.g., Member of the Amer. Pharmaceutical 
Association. In Preparation. 



Bound in Cloth, each $1.00. Interleaved, for the Addition of Notes, $1.25. 
These books are constantly revised to keep up with the latest teachings and discoveries. 



P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. 



NOW READY FOR 1886. 

The Physician's Visiting List. 

(LINDSAY & BLAKISTON'S.) 

PUBLISHED ANNUALLY; NOW IN ITS THIRTY-FIFTH YEAR. 

Containing Calendar, List of Poisons and Antidotes, Dose Tables rewritten in accord- 
ance with the Sixth Revision of the U. S. Pharmacopoeia, Marshall Hall's Ready- 
Method in Asphyxia, Lists of New Remedies, Sylvester's Method for Producing 
Artificial Respiration, with Illustrations ; Diagram for Diagnosing Diseases of 
Heart and Lungs ; a new Table for Calculating the Period of Utero-Gestation, etc. 

$^ a The Quality of the Leather used in Binding this List has been again Improved, and a 
Superior Pencil, with Nickel Tip, manufactured especially for it, has been added. 

SIZES AND PRICES. 

For 25 Patients weekly. Tucks, pockets, etc., $1.00 

50 " " ' « « 1.25 

75 " " " " 1.50 

ioo " " « " 2.00 

,, ,, T7 - , C Tan. to June ") 

5° 2 Vols. 1 i , . L [ 2. so 

3 \ July to Dec. \ ° 

u ce \t i T J an - to June f 

2Vo!s - I July to Dec. I 3-°° 

INTERLEAVED EDITION. 

For 25 Patients weekly. Interleaved, tucks, etc., 1.25 

50 " " ' " 1.50 

it te vi f J an - to June ) 

5° 2Vols - J July to Dec.} 3-°o 

Perpetual Edition, without Dates, can be commenced at any time and used until full, similar 
in style, contents and arrangements to the above. 

For 25 Patients, Interleaved, $1.25 
" 50 « « 1.50 

" For completeness, compactness, and simplicity of arrangement it is excelled by none in the market." — N. V. 
Medical Record. 

" The book is convenient in form, not too bulky, and in every respect the very best Visiting List published."— 
Canada Medical and Surgical Journal. 

" After all the trials made, there are none superior to it." — Gaillard's Medical Journal. 

" It has become Standard."" — Southern Clinic. 

" Regular as the seasons comes this old favorite." — Michigan Medical News. 

" It is quite convenient for the pocket, and possesses every desirable quality." — Medical Herald. 

"The most popular Visiting List extant.'' — Buffalo Medical and Surgical Journal. 

" We have used it for years, and do not hesitate to pronounce it equal, if not superior, to any." — Southern Clinic. 

"This Visiting List is too well known to require either description or commendation from us." — Cincinnati 
Medical News. 

WATSON'S 

Physician's Ledger and Cash Book Combined. 

WEEKLY AND MONTHLY. 

This Ledger is based upon, and designed to be used in connection with, Lindsay & 
Blakiston's Physician's Visiting List. 

PRICES. 

Ledger for 1000 accounts, Leather, $6.50 

" 500 " " 5.00 

" 500 " Cloth, 4.00 

*** Sample pages of both books sent upon application. Books sent, postage pre- 
paid, upon receipt of full price, or can be obtained through any bookseller. 

P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. 



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